Implement Melee-style knockback stacking (#97)

## Summary

- stack residual airborne knockback per axis after the configured launch-frame threshold
- apply DI after combining the launch vectors while retaining the second hit's hitstun
- preserve and decay residual knockback after hitstun
- make stacking state rollback-safe and include it in debug save states
- clear launch state on landing, ledge interactions, KO, and respawn

## Testing

- `cargo check --tests`
- `cargo test` (159 tests passed)
- `git diff --check`

## Asset configuration

For Melee timing, `knockback_stacking_window` should be set to `10`. The local ignored asset package has been updated accordingly.

Reviewed-on: #97
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/debug_tools/save_state.rs

@@ -1,12 +1,26 @@
 use bevy::prelude::*;
 
 use crate::{
-    camera::MatchCamera, fighter::{
+    camera::MatchCamera,
-        FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop, FighterHitstopShake, FighterInvulnerabilityState, FighterPendingRespawn, FighterPreviousFacingDirection, FighterPreviousTranslation, FighterSurfaceState, FighterTranslation, FighterVelocity, animation::FighterAnimationFrame, attack::{
+    fighter::{
-            FighterDamage, FighterKnockbackVelocity, FighterPendingHitReaction, FighterPendingHits,
+        FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop, FighterHitstopShake,
-            FighterSolvedHurtboxes, FighterStaleMoveQueue,
+        FighterInvulnerabilityState, FighterLedgeInformation, FighterPendingRespawn,
-        }, baked_animation::FighterBoneMatrices, state::FighterState,
+        FighterPreviousFacingDirection, FighterPreviousTranslation, FighterSurfaceState,
-    }, input::FighterInput, match_runtime::MatchState, player::Player, stage::line::StageCollision,
+        FighterTranslation, FighterVelocity,
+        animation::FighterAnimationFrame,
+        attack::{
+            FighterDamage, FighterKnockbackState, FighterKnockbackVelocity,
+            FighterPendingHitReaction, FighterPendingHits, FighterSolvedHurtboxes,
+            FighterStaleMoveQueue,
+        },
+        baked_animation::FighterBoneMatrices,
+        ecb::FighterDesiredECB,
+        state::FighterState,
+    },
+    input::FighterInput,
+    match_runtime::MatchState,
+    player::Player,
+    stage::line::StageCollision,
 };
 
 #[derive(Resource, Default)]
@@ -27,6 +41,7 @@ struct FighterCheckpoint {
     entity: Entity,
     handle: usize,
     ecb: FighterECB,
+    desired_ecb: FighterDesiredECB,
     previous_ecb: crate::fighter::ecb::FighterPreviousECB,
     velocity: FighterVelocity,
     translation: FighterTranslation,
@@ -41,6 +56,7 @@ struct FighterCheckpoint {
     hitstop: FighterHitstop,
     hitstop_shake: FighterHitstopShake,
     knockback_velocity: FighterKnockbackVelocity,
+    knockback_state: FighterKnockbackState,
     stale_moves: FighterStaleMoveQueue,
     hitboxes: FighterHitboxes,
     solved_hurtboxes: FighterSolvedHurtboxes,
@@ -48,6 +64,7 @@ struct FighterCheckpoint {
     surface: FighterSurfaceState,
     pending_respawn: FighterPendingRespawn,
     invulnerability_state: FighterInvulnerabilityState,
+    ledge_information: FighterLedgeInformation,
 }
 
 pub(super) fn save_or_restore(world: &mut World) {
@@ -130,6 +147,7 @@ pub(super) fn save_or_restore(world: &mut World) {
 
         let mut entity = world.entity_mut(saved.entity);
         entity.insert(saved.ecb);
+        entity.insert(saved.desired_ecb);
         entity.insert(saved.previous_ecb);
         entity.insert(saved.velocity);
         entity.insert(saved.translation);
@@ -144,6 +162,7 @@ pub(super) fn save_or_restore(world: &mut World) {
         entity.insert(saved.hitstop);
         entity.insert(saved.hitstop_shake);
         entity.insert(saved.knockback_velocity);
+        entity.insert(saved.knockback_state);
         entity.insert(saved.stale_moves.clone());
         entity.insert(saved.hitboxes.clone());
         entity.insert(saved.solved_hurtboxes.clone());
@@ -151,6 +170,7 @@ pub(super) fn save_or_restore(world: &mut World) {
         entity.insert(saved.surface.clone());
         entity.insert(saved.pending_respawn.clone());
         entity.insert(saved.invulnerability_state.clone());
+        entity.insert(saved.ledge_information.clone());
     }
     world.insert_resource(checkpoint.pending_hits.clone());
     world.insert_resource(checkpoint.stage_collision);
@@ -167,6 +187,7 @@ fn capture_fighter(world: &World, entity: Entity) -> Option<FighterCheckpoint> {
         entity,
         handle: fighter.get::<Player>()?.handle,
         ecb: *fighter.get::<FighterECB>()?,
+        desired_ecb: *fighter.get::<FighterDesiredECB>()?,
         previous_ecb: *fighter.get::<crate::fighter::ecb::FighterPreviousECB>()?,
         velocity: *fighter.get::<FighterVelocity>()?,
         translation: *fighter.get::<FighterTranslation>()?,
@@ -181,6 +202,7 @@ fn capture_fighter(world: &World, entity: Entity) -> Option<FighterCheckpoint> {
         hitstop: *fighter.get::<FighterHitstop>()?,
         hitstop_shake: *fighter.get::<FighterHitstopShake>()?,
         knockback_velocity: *fighter.get::<FighterKnockbackVelocity>()?,
+        knockback_state: *fighter.get::<FighterKnockbackState>()?,
         stale_moves: fighter.get::<FighterStaleMoveQueue>()?.clone(),
         hitboxes: fighter.get::<FighterHitboxes>()?.clone(),
         solved_hurtboxes: fighter.get::<FighterSolvedHurtboxes>()?.clone(),
@@ -188,6 +210,7 @@ fn capture_fighter(world: &World, entity: Entity) -> Option<FighterCheckpoint> {
         surface: fighter.get::<FighterSurfaceState>()?.clone(),
         pending_respawn: fighter.get::<FighterPendingRespawn>()?.clone(),
         invulnerability_state: fighter.get::<FighterInvulnerabilityState>()?.clone(),
+        ledge_information: fighter.get::<FighterLedgeInformation>()?.clone(),
     })
 }
 

src/fighter/animation.rs

@@ -104,6 +104,7 @@ pub enum AnimKind {
     AttackDownTilt,
     AttackNeutralAir,
     AttackForwardAir,
+    AttackDownAir,
     AttackDash,
     AttackUpSmash,
 }

src/fighter/attack/directional_influence.rs

@@ -15,6 +15,16 @@ pub fn apply_directional_influence(
     let (sin, cos) = attack_angle.sin_cos();
     let base_launch_direction = FGVec2::new(cos, sin);
 
+    apply_directional_influence_to_direction(receiver_stick, base_launch_direction, di_max_angle)
+}
+
+/// Applies DI to an already-computed launch direction. This is used after
+/// knockback stacking, where the resulting angle may differ from either hit.
+pub fn apply_directional_influence_to_direction(
+    receiver_stick: FGVec2,
+    base_launch_direction: FGVec2,
+    di_max_angle: FGi32,
+) -> FGVec2 {
     let Some(base_launch_direction) = base_launch_direction.normalize() else {
         return FGVec2::ZERO;
     };
@@ -30,14 +40,20 @@ pub fn apply_directional_influence(
         -di_max_angle.to_fixed::<FGWide>(),
         di_max_angle.to_fixed::<FGWide>(),
     );
-    let (sin, cos) = (attack_angle + angle_change.to_fixed::<FGi32>()).sin_cos();
+    let (sin, cos) = angle_change.to_fixed::<FGi32>().sin_cos();
-    FGVec2::new(cos, sin).normalize_or_zero()
+    FGVec2::new(
+        base_launch_direction.x * cos - base_launch_direction.y * sin,
+        base_launch_direction.x * sin + base_launch_direction.y * cos,
+    )
+    .normalize_or_zero()
 }
 
 #[cfg(test)]
 mod test {
     use crate::{
-        fighter::attack::directional_influence::apply_directional_influence,
+        fighter::attack::directional_influence::{
+            apply_directional_influence, apply_directional_influence_to_direction,
+        },
         math::{int::FGi32, vec::FGVec2},
     };
 
@@ -66,4 +82,17 @@ mod test {
         assert!(di.x > FGi32::ZERO);
         assert!(di.y < FGi32::ZERO);
     }
+
+    #[test]
+    fn vector_di_preserves_a_stacked_direction_without_input() {
+        let direction = FGVec2::lit("-0.6", "0.8");
+        let result = apply_directional_influence_to_direction(
+            FGVec2::ZERO,
+            direction,
+            FGi32::lit("18.0"),
+        );
+        const EPSILON: FGi32 = FGi32::from_bits(6);
+        assert!(result.x.abs_diff(direction.x) < EPSILON);
+        assert!(result.y.abs_diff(direction.y) < EPSILON);
+    }
 }

src/fighter/attack/mod.rs

@@ -33,6 +33,75 @@ use crate::{
 #[derive(Deref, Component, Default, Hash, Debug, Copy, Clone)]
 pub struct FighterKnockbackVelocity(pub FGVec2);
 
+/// Lifecycle state for the currently active launch velocity.
+///
+/// This counts frames where knockback was actually applied to movement; hitstop
+/// therefore does not advance it. Melee uses this age to decide whether a
+/// subsequent airborne hit replaces or stacks with the previous launch.
+#[derive(Component, Default, Hash, Debug, Copy, Clone)]
+pub struct FighterKnockbackState {
+    pub frames_since_launch: u32,
+}
+
+impl FighterKnockbackState {
+    pub fn restart(&mut self) {
+        self.frames_since_launch = 0;
+    }
+
+    pub fn clear(&mut self) {
+        self.frames_since_launch = 0;
+    }
+
+    pub fn advance(&mut self) {
+        self.frames_since_launch = self.frames_since_launch.saturating_add(1);
+    }
+
+    pub fn can_stack(&self, minimum_frames: u32) -> bool {
+        self.frames_since_launch >= minimum_frames
+    }
+}
+
+fn stack_knockback_component(previous: FGi32, new: FGi32) -> FGi32 {
+    if previous.is_zero() {
+        return new;
+    }
+    if new.is_zero() {
+        return previous;
+    }
+
+    if previous.signum() != new.signum() {
+        previous + new
+    } else if previous.abs() > new.abs() {
+        previous
+    } else {
+        new
+    }
+}
+
+/// Applies Melee's knockback-stacking rule independently to both axes.
+pub fn stack_knockback(previous: FGVec2, new: FGVec2) -> FGVec2 {
+    FGVec2::new(
+        stack_knockback_component(previous.x, new.x),
+        stack_knockback_component(previous.y, new.y),
+    )
+}
+
+pub fn decay_knockback(
+    velocity: &mut FighterKnockbackVelocity,
+    state: &mut FighterKnockbackState,
+    decay_per_frame: FGi32,
+) {
+    let speed = velocity.length();
+    let next_speed = speed.saturating_sub(decay_per_frame).max(FGi32::ZERO);
+    velocity.0 = velocity.normalize_or_zero() * next_speed;
+
+    if next_speed.is_zero() {
+        state.clear();
+    } else {
+        state.advance();
+    }
+}
+
 #[derive(Debug, Default, Clone, Copy, Serialize, Deserialize, Component, Hash, PartialEq, Eq, PartialOrd, Ord)]
 pub struct FighterDamage(FGi32);
 
@@ -73,6 +142,53 @@ pub struct FighterLastAttackDebug {
     pub trajectory_points: Vec<Vec3>,
 }
 
+#[cfg(test)]
+mod knockback_stacking_tests {
+    use super::*;
+
+    #[test]
+    fn same_direction_keeps_the_stronger_component() {
+        assert_eq!(
+            stack_knockback(FGVec2::lit("3", "8"), FGVec2::lit("5", "4")),
+            FGVec2::lit("5", "8")
+        );
+    }
+
+    #[test]
+    fn opposing_components_add_independently() {
+        assert_eq!(
+            stack_knockback(FGVec2::lit("3", "8"), FGVec2::lit("-5", "-3")),
+            FGVec2::lit("-2", "5")
+        );
+    }
+
+    #[test]
+    fn opposing_components_can_cancel() {
+        assert_eq!(
+            stack_knockback(FGVec2::lit("3", "-4"), FGVec2::lit("-3", "4")),
+            FGVec2::ZERO
+        );
+    }
+
+    #[test]
+    fn zero_components_preserve_the_nonzero_value() {
+        assert_eq!(
+            stack_knockback(FGVec2::lit("0", "2"), FGVec2::lit("-3", "0")),
+            FGVec2::lit("-3", "2")
+        );
+    }
+
+    #[test]
+    fn stacking_threshold_is_inclusive() {
+        let mut state = FighterKnockbackState {
+            frames_since_launch: 9,
+        };
+        assert!(!state.can_stack(10));
+        state.advance();
+        assert!(state.can_stack(10));
+    }
+}
+
 #[derive(Debug, Default, Clone, Deref, DerefMut, Hash, PartialEq, PartialOrd)]
 pub struct HitStop(u32);
 
@@ -231,8 +347,8 @@ impl AttackKind {
             AttackKind::Jab => AnimKind::AttackJab1,
             AttackKind::UpTilt => AnimKind::AttackUpTilt,
             AttackKind::ForwardAir => AnimKind::AttackForwardAir,
+            AttackKind::DownAir => AnimKind::AttackDownAir,
             AttackKind::BackAir => AnimKind::AttackUpTilt,
-            AttackKind::DownAir => AnimKind::AttackUpTilt,
             AttackKind::UpAir => AnimKind::AttackUpTilt,
             AttackKind::DownTilt => AnimKind::AttackDownTilt,
             AttackKind::ForwardTilt => AnimKind::AttackForwardTilt,

src/fighter/collision.rs

@@ -1,11 +1,17 @@
 //! Resolving an integrated fighter position against the stage.
 
-use crate::fighter::ecb::FighterPreviousECB;
+use crate::fighter::ecb::{self as ecb_module, FighterDesiredECB};
-use crate::fighter::{FighterECB, FighterPreviousTranslation, FighterTranslation};
+use crate::fighter::{FighterPreviousTranslation, FighterTranslation};
+use crate::fighter::FighterVelocity;
+#[cfg(test)]
+use crate::fighter::{FighterECB, ecb::FighterPreviousECB};
+use crate::math::int::FGi32;
 use crate::math::rect::FGRect;
 use crate::math::segment::FGSegment2d;
 use crate::math::vec::FGVec2;
-use crate::stage::line::{StageCollision, StageLineID, StagePolyType, StageVertexID};
+use crate::stage::line::{
+    StageCollision, StageLineID, StagePolyLineSegmentType, StagePolyType, StageVertexID,
+};
 /*
 pub fn collide_fighter_with_scene(
     fighters: Query<(&FighterECB, &mut FighterVelocity, &mut FighterTranslation)>,
@@ -36,54 +42,395 @@ pub fn collide_fighter_with_scene(
 pub struct AirCollisionWithStageResult {
     pub line_id: StageLineID,
     pub hit_position: FGVec2,
+    /// Fighter origin at the collision substep. The ECB remains local to this
+    /// origin; callers must not rebase the ECB by the frame-sized movement.
+    pub resolved_translation: FGVec2,
     pub hit_normal: FGVec2,
 }
 
-pub fn air_collide_with_stage(
+#[derive(Clone, Copy, Debug, Default)]
+pub struct AirCollisionOptions {
+    /// Allow downward input to disable collision with pass-through platforms.
+    pub can_pass_through_soft_platforms: bool,
+    /// Treat an upward crossing of a pass-through platform by the ECB bottom as a landing.
+    pub land_on_soft_platforms_from_below: bool,
+}
+
+#[cfg(test)]
+fn air_collide_with_stage(
     prev_translation: &FighterPreviousTranslation,
     translation: &FighterTranslation,
     prev_ecb: &FighterPreviousECB,
     ecb: &FighterECB,
     stage_collision: &StageCollision,
     ignored_polys: &[usize],
-    can_ignore_soft_platforms: bool,
+    options: AirCollisionOptions,
 ) -> Option<AirCollisionWithStageResult> {
-    let ray_segment = FGSegment2d::new(
+    let mut translation = *translation;
-        prev_translation.0 + prev_ecb.get_bottom_point(),
+    let mut velocity = FighterVelocity::default();
-        translation.0 + ecb.get_bottom_point(),
+    air_collide_with_stage_substepped(
-    );
+        prev_translation,
+        &mut translation,
+        &mut velocity,
+        &mut ecb_module::FighterECB {
+            top: prev_ecb.top,
+            bottom: prev_ecb.bottom,
+            left: prev_ecb.left,
+            right: prev_ecb.right,
+        },
+        &FighterDesiredECB::from(*ecb),
+        stage_collision,
+        ignored_polys,
+        options,
+    )
+}
+
+/// Sweeps movement and ECB shape changes together.
+pub(crate) fn collision_step_count(max_change: FGi32) -> u32 {
+    let six = FGi32::lit("6.0");
+    if max_change <= six {
+        return 1;
+    }
+
+    let mut quotient = 0;
+    let mut remainder = max_change;
+    while remainder >= six {
+        quotient += 1;
+        remainder -= six;
+    }
+    quotient + 1
+}
+
+pub fn air_collide_with_stage_substepped(
+    prev_translation: &FighterPreviousTranslation,
+    translation: &mut FighterTranslation,
+    velocity: &mut FighterVelocity,
+    ecb: &mut crate::fighter::FighterECB,
+    desired: &FighterDesiredECB,
+    stage_collision: &StageCollision,
+    ignored_polys: &[usize],
+    options: AirCollisionOptions,
+) -> Option<AirCollisionWithStageResult> {
+    let requested_translation = translation.0;
+    let movement = requested_translation - prev_translation.0;
+    let mut largest_change = movement.x.abs().max(movement.y.abs());
+    largest_change = largest_change.max(ecb_module::ecb_max_delta(ecb, desired));
+    let steps = collision_step_count(largest_change);
+
+    let step_count = FGi32::from_num(steps);
+    let movement_per_step = movement / step_count;
+    let mut current_position = prev_translation.0;
+    let mut current_ecb = *ecb;
+    let mut collision_offset = FGVec2::ZERO;
+
+    for step in 0..steps {
+        let previous_position = current_position;
+        let previous_ecb = current_ecb;
+        let remaining_steps = FGi32::from_num(steps - step);
+        ecb_module::interpolate_ecb(&mut current_ecb, *desired, FGi32::ONE / remaining_steps);
+        current_position = if step + 1 == steps {
+            // Fixed-point division may truncate. Always make the final
+            // substep land exactly on the requested frame endpoint.
+            requested_translation + collision_offset
+        } else {
+            prev_translation.0
+                + movement_per_step * FGi32::from_num(step + 1)
+                + collision_offset
+        };
+
+        let lower_edges = [
+            (
+                previous_ecb.bottom,
+                previous_ecb.left,
+                current_ecb.bottom,
+                current_ecb.left,
+            ),
+            (
+                previous_ecb.bottom,
+                previous_ecb.right,
+                current_ecb.bottom,
+                current_ecb.right,
+            ),
+        ];
+        if let Some(result) = sweep_edges(
+            stage_collision,
+            previous_position,
+            current_position,
+            &lower_edges,
+            StagePolyLineSegmentType::Floor,
+            ignored_polys,
+            options.can_pass_through_soft_platforms,
+        ) {
+            *ecb = current_ecb;
+            translation.0 = current_position + result.correction;
+            velocity.0 -= velocity.0.project_onto_normalized(result.hit_normal);
+            let bottom_contact = translation.0 + current_ecb.bottom;
+            return Some(AirCollisionWithStageResult {
+                line_id: result.line_id,
+                hit_position: bottom_contact,
+                resolved_translation: translation.0,
+                hit_normal: result.hit_normal,
+            });
+        }
+
+        let upper_edges = [
+            (
+                previous_ecb.top,
+                previous_ecb.left,
+                current_ecb.top,
+                current_ecb.left,
+            ),
+            (
+                previous_ecb.top,
+                previous_ecb.right,
+                current_ecb.top,
+                current_ecb.right,
+            ),
+        ];
+        if let Some(contact) = sweep_edges(
+            stage_collision,
+            previous_position,
+            current_position,
+            &upper_edges,
+            StagePolyLineSegmentType::Ceiling,
+            ignored_polys,
+            true,
+        ) {
+            current_position += contact.correction;
+            collision_offset += contact.correction;
+            velocity.0 -= velocity.0.project_onto_normalized(contact.hit_normal);
+        }
+
+        if options.land_on_soft_platforms_from_below
+            && let Some(result) = sweep_bottom_point_through_platforms(
+                stage_collision,
+                previous_position + previous_ecb.bottom,
+                current_position + current_ecb.bottom,
+                ignored_polys,
+            )
+        {
+            *ecb = current_ecb;
+            translation.0 = current_position + result.correction;
+            velocity.0 -= velocity.0.project_onto_normalized(result.hit_normal);
+            let bottom_contact = translation.0 + current_ecb.bottom;
+            return Some(AirCollisionWithStageResult {
+                line_id: result.line_id,
+                hit_position: bottom_contact,
+                resolved_translation: translation.0,
+                hit_normal: result.hit_normal,
+            });
+        }
+
+        let side_edges = [
+            (
+                previous_ecb.bottom,
+                previous_ecb.right,
+                current_ecb.bottom,
+                current_ecb.right,
+            ),
+            (
+                previous_ecb.right,
+                previous_ecb.top,
+                current_ecb.right,
+                current_ecb.top,
+            ),
+            (
+                previous_ecb.top,
+                previous_ecb.left,
+                current_ecb.top,
+                current_ecb.left,
+            ),
+            (
+                previous_ecb.left,
+                previous_ecb.bottom,
+                current_ecb.left,
+                current_ecb.bottom,
+            ),
+        ];
+        if let Some(contact) = sweep_edges(
+            stage_collision,
+            previous_position,
+            current_position,
+            &side_edges,
+            StagePolyLineSegmentType::Wall,
+            ignored_polys,
+            true,
+        ) {
+            current_position += contact.correction;
+            collision_offset += contact.correction;
+            velocity.0 -= velocity.0.project_onto_normalized(contact.hit_normal);
+        }
+    }
+
+    *ecb = current_ecb;
+    translation.0 = current_position;
+    None
+}
+
+struct PointSweepResult {
+    line_id: StageLineID,
+    hit_normal: FGVec2,
+    correction: FGVec2,
+}
+
+fn sweep_bottom_point_through_platforms(
+    stage_collision: &StageCollision,
+    previous_bottom: FGVec2,
+    current_bottom: FGVec2,
+    ignored_polys: &[usize],
+) -> Option<PointSweepResult> {
+    let bottom_sweep = FGSegment2d::new(previous_bottom, current_bottom);
 
     stage_collision
         .stage_polys
         .iter()
         .enumerate()
         .filter(|(poly_idx, poly)| {
-            !ignored_polys.contains(poly_idx)
+            !ignored_polys.contains(poly_idx) && matches!(poly.poly_type, StagePolyType::Platform)
-                && !(can_ignore_soft_platforms && matches!(poly.poly_type, StagePolyType::Platform))
         })
-        .filter_map(|(poly_idx, poly)| {
+        .flat_map(|(poly_idx, poly)| {
-            poly.intersect_ray(ray_segment).map(|intersect_result| {
+            poly.segments
-                (
+                .iter()
-                    AirCollisionWithStageResult {
+                .enumerate()
-                        line_id: {
+                .filter(|(_, segment)| {
-                            StageLineID {
+                    matches!(segment.segment_type, StagePolyLineSegmentType::Floor)
+                })
+                .filter_map(move |(segment_idx, segment)| {
+                    let previous_distance = segment
+                        .normal
+                        .dot(previous_bottom - segment.segment.point1());
+                    let current_distance = segment
+                        .normal
+                        .dot(current_bottom - segment.segment.point1());
+                    if previous_distance >= crate::math::int::FGWide::ZERO
+                        || current_distance < crate::math::int::FGWide::ZERO
+                    {
+                        return None;
+                    }
+
+                    let hit_position = segment.segment.segment_intersection(&bottom_sweep)?;
+                    Some((
+                        PointSweepResult {
+                            line_id: StageLineID {
                                 polygon: poly_idx,
-                                segment: intersect_result.segment_idx,
+                                segment: segment_idx,
-                            }
+                            },
+                            hit_normal: segment.normal,
+                            correction: hit_position - current_bottom,
                         },
-                        hit_position: intersect_result.position,
+                        hit_position.distance_squared(previous_bottom),
-                        hit_normal: intersect_result.normal,
+                    ))
-                    },
+                })
-                    intersect_result
+        })
-                        .position
+        .min_by_key(|(_, distance)| *distance)
-                        .distance_squared(ray_segment.point2()),
+        .map(|(result, _)| result)
-                )
+}
-            })
+
+fn sweep_edges(
+    stage_collision: &StageCollision,
+    previous_position: FGVec2,
+    current_position: FGVec2,
+    edges: &[(FGVec2, FGVec2, FGVec2, FGVec2)],
+    segment_type: StagePolyLineSegmentType,
+    ignored_polys: &[usize],
+    ignore_platforms: bool,
+) -> Option<PointSweepResult> {
+    stage_collision
+        .stage_polys
+        .iter()
+        .enumerate()
+        .filter(|(poly_idx, poly)| {
+            !ignored_polys.contains(poly_idx)
+                && !(ignore_platforms && matches!(poly.poly_type, StagePolyType::Platform))
+        })
+        .flat_map(|(poly_idx, poly)| {
+            poly.segments
+                .iter()
+                .enumerate()
+                .filter(move |(_, segment)| segment.segment_type == segment_type)
+                .filter_map(move |(segment_idx, segment)| {
+                    edges
+                        .iter()
+                        .filter_map(|(previous_a, previous_b, current_a, current_b)| {
+                            let previous_a = previous_position + *previous_a;
+                            let previous_b = previous_position + *previous_b;
+                            let current_a = current_position + *current_a;
+                            let current_b = current_position + *current_b;
+                            let previous_min = segment
+                                .normal
+                                .dot(previous_a - segment.segment.point1())
+                                .min(segment.normal.dot(previous_b - segment.segment.point1()));
+                            let current_a_distance =
+                                segment.normal.dot(current_a - segment.segment.point1());
+                            let current_b_distance =
+                                segment.normal.dot(current_b - segment.segment.point1());
+                            let current_min = current_a_distance.min(current_b_distance);
+                            if previous_min < crate::math::int::FGWide::ZERO
+                                || current_min > crate::math::int::FGWide::ZERO
+                            {
+                                return None;
+                            }
+
+                            let boundary = [
+                                FGSegment2d::new(previous_a, previous_b),
+                                FGSegment2d::new(previous_a, current_a),
+                                FGSegment2d::new(previous_b, current_b),
+                                FGSegment2d::new(current_a, current_b),
+                            ];
+                            let quad = [previous_a, previous_b, current_b, current_a];
+                            let position = boundary
+                                .iter()
+                                .filter_map(|edge| segment.segment.segment_intersection(edge))
+                                .max_by_key(|position| position.distance_squared(current_a))
+                                .or_else(|| {
+                                    [segment.segment.point1(), segment.segment.point2()]
+                                        .into_iter()
+                                        .find(|point| point_in_convex_quad(*point, quad))
+                                })?;
+                            let penetration = FGi32::from_num(-current_min);
+                            Some((position, segment.normal * penetration))
+                        })
+                        .max_by_key(|(position, _)| {
+                            position.distance_squared(segment.segment.point1())
+                        })
+                        .map(|(position, correction)| {
+                            (
+                                PointSweepResult {
+                                    line_id: StageLineID {
+                                        polygon: poly_idx,
+                                        segment: segment_idx,
+                                    },
+                                    hit_normal: segment.normal,
+                                    correction,
+                                },
+                                position.distance_squared(segment.segment.point2()),
+                            )
+                        })
+                })
         })
         .max_by(|(_, a), (_, b)| a.cmp(b))
         .map(|(result, _)| result)
 }
 
+fn point_in_convex_quad(point: FGVec2, quad: [FGVec2; 4]) -> bool {
+    let mut has_positive = false;
+    let mut has_negative = false;
+    for (a, b) in quad.into_iter().zip(quad.into_iter().cycle().skip(1)).take(4) {
+        let edge = b - a;
+        let offset = point - a;
+        let cross = crate::math::int::FGWide::from_num(edge.x)
+            * crate::math::int::FGWide::from_num(offset.y)
+            - crate::math::int::FGWide::from_num(edge.y)
+                * crate::math::int::FGWide::from_num(offset.x);
+        has_positive |= cross > crate::math::int::FGWide::ZERO;
+        has_negative |= cross < crate::math::int::FGWide::ZERO;
+        if has_positive && has_negative {
+            return false;
+        }
+    }
+    true
+}
+
 #[derive(Clone)]
 pub struct AirCollisionWithLedgeResult {
     pub ledge: StageVertexID,
@@ -93,9 +440,11 @@ pub fn air_collide_with_ledges(
     ledge_box: &FGRect,
     stage_collision: &StageCollision,
 ) -> Option<AirCollisionWithLedgeResult> {
-    stage_collision.intersect_ledges(ledge_box).map(|result| {
+    stage_collision
-        AirCollisionWithLedgeResult { ledge: result.vertex_id }
+        .intersect_ledges(ledge_box)
-    })
+        .map(|result| AirCollisionWithLedgeResult {
+            ledge: result.vertex_id,
+        })
 }
 
 #[cfg(test)]
@@ -126,6 +475,173 @@ mod tests {
         )
     }
 
+    fn single_segment(
+        start: FGVec2,
+        end: FGVec2,
+        segment_type: StagePolyLineSegmentType,
+    ) -> StagePoly {
+        let segment = FGSegment2d::new(start, end);
+        StagePoly {
+            poly_type: StagePolyType::Closed,
+            segments: vec![crate::stage::line::StagePolyLineSegment {
+                segment,
+                normal: segment.left_normal(),
+                segment_type,
+            }],
+        }
+    }
+
+    #[test]
+    fn melee_step_count_adds_one_step_after_each_six_unit_block() {
+        assert_eq!(collision_step_count(FGi32::lit("6")), 1);
+        assert_eq!(collision_step_count(FGi32::lit("6.01")), 2);
+        assert_eq!(collision_step_count(FGi32::lit("12")), 3);
+        assert_eq!(collision_step_count(FGi32::lit("18")), 4);
+    }
+
+    #[test]
+    fn collision_result_keeps_ecb_local_to_resolved_origin() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![horizontal_platform("0")],
+            ..StageCollision::default()
+        };
+        let previous_translation = FighterPreviousTranslation(FGVec2::lit("0", "2"));
+        let mut translation = FighterTranslation(FGVec2::lit("0", "-1"));
+        let mut velocity = FighterVelocity(FGVec2::lit("0", "-3"));
+        let mut ecb = FighterECB {
+            top: FGVec2::lit("0", "2"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-1", "0.5"),
+            right: FGVec2::lit("1", "0.5"),
+        };
+        let desired = FighterDesiredECB::from(ecb);
+        let collision = air_collide_with_stage_substepped(
+            &previous_translation,
+            &mut translation,
+            &mut velocity,
+            &mut ecb,
+            &desired,
+            &stage_collision,
+            &[],
+            Default::default(),
+        )
+        .expect("the floor should be hit");
+
+        assert_eq!(
+            collision.resolved_translation + ecb.bottom,
+            collision.hit_position
+        );
+        assert_eq!(velocity.0.y, FGi32::ZERO);
+    }
+
+    #[test]
+    fn airborne_side_point_resolves_wall_and_projects_velocity() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![single_segment(
+                FGVec2::lit("2", "2"),
+                FGVec2::lit("2", "-2"),
+                StagePolyLineSegmentType::Wall,
+            )],
+            ..StageCollision::default()
+        };
+        let previous = FighterPreviousTranslation(FGVec2::lit("4", "0"));
+        let mut translation = FighterTranslation(FGVec2::lit("0", "0"));
+        let mut velocity = FighterVelocity(FGVec2::lit("-4", "0"));
+        let mut ecb = FighterECB {
+            top: FGVec2::lit("0", "1"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-1", "0"),
+            right: FGVec2::lit("1", "0"),
+        };
+        let desired = FighterDesiredECB::from(ecb);
+
+        assert!(air_collide_with_stage_substepped(
+            &previous,
+            &mut translation,
+            &mut velocity,
+            &mut ecb,
+            &desired,
+            &stage_collision,
+            &[],
+            Default::default(),
+        )
+        .is_none());
+        assert_eq!(translation.0, FGVec2::lit("3", "0"));
+        assert_eq!(velocity.0.x, FGi32::ZERO);
+    }
+
+    #[test]
+    fn stage_corner_cannot_pass_through_middle_of_diamond_edge() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![single_segment(
+                FGVec2::lit("2", "0.6"),
+                FGVec2::lit("2", "0.4"),
+                StagePolyLineSegmentType::Wall,
+            )],
+            ..StageCollision::default()
+        };
+        let previous = FighterPreviousTranslation(FGVec2::lit("4", "0"));
+        let mut translation = FighterTranslation(FGVec2::ZERO);
+        let mut velocity = FighterVelocity(FGVec2::lit("-4", "0"));
+        let mut ecb = FighterECB {
+            top: FGVec2::lit("0", "1"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-1", "0"),
+            right: FGVec2::lit("1", "0"),
+        };
+        let desired = FighterDesiredECB::from(ecb);
+
+        assert!(air_collide_with_stage_substepped(
+            &previous,
+            &mut translation,
+            &mut velocity,
+            &mut ecb,
+            &desired,
+            &stage_collision,
+            &[],
+            Default::default(),
+        )
+        .is_none());
+        assert_eq!(translation.0.x, FGi32::lit("3"));
+        assert_eq!(velocity.0.x, FGi32::ZERO);
+    }
+
+    #[test]
+    fn airborne_top_point_resolves_ceiling_and_projects_velocity() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![single_segment(
+                FGVec2::lit("2", "2"),
+                FGVec2::lit("-2", "2"),
+                StagePolyLineSegmentType::Ceiling,
+            )],
+            ..StageCollision::default()
+        };
+        let previous = FighterPreviousTranslation(FGVec2::ZERO);
+        let mut translation = FighterTranslation(FGVec2::lit("0", "4"));
+        let mut velocity = FighterVelocity(FGVec2::lit("0", "4"));
+        let mut ecb = FighterECB {
+            top: FGVec2::lit("0", "1"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-1", "0"),
+            right: FGVec2::lit("1", "0"),
+        };
+        let desired = FighterDesiredECB::from(ecb);
+
+        assert!(air_collide_with_stage_substepped(
+            &previous,
+            &mut translation,
+            &mut velocity,
+            &mut ecb,
+            &desired,
+            &stage_collision,
+            &[],
+            Default::default(),
+        )
+        .is_none());
+        assert_eq!(translation.0, FGVec2::lit("0", "1"));
+        assert_eq!(velocity.0.y, FGi32::ZERO);
+    }
+
     #[test]
     fn airborne_collision_skips_ignored_polygons() {
         let stage_collision = StageCollision {
@@ -154,7 +670,7 @@ mod tests {
             &ecb,
             &stage_collision,
             &[1],
-            false,
+            Default::default(),
         )
         .expect("the non-ignored platform should still be collidable");
 
@@ -183,16 +699,21 @@ mod tests {
             right: FGVec2::ZERO,
         };
 
-        assert!(air_collide_with_stage(
+        assert!(
-            &previous_translation,
+            air_collide_with_stage(
-            &translation,
+                &previous_translation,
-            &previous_ecb,
+                &translation,
-            &ecb,
+                &previous_ecb,
-            &stage_collision,
+                &ecb,
-            &[],
+                &stage_collision,
-            true,
+                &[],
-        )
+                AirCollisionOptions {
-        .is_none());
+                    can_pass_through_soft_platforms: true,
+                    ..Default::default()
+                },
+            )
+            .is_none()
+        );
 
         assert_eq!(
             air_collide_with_stage(
@@ -202,7 +723,7 @@ mod tests {
                 &ecb,
                 &stage_collision,
                 &[],
-                false,
+                Default::default(),
             )
             .expect("air dodges still collide with soft platforms")
             .hit_position,
@@ -238,11 +759,131 @@ mod tests {
             &ecb,
             &stage_collision,
             &[],
-            true,
+            AirCollisionOptions {
+                can_pass_through_soft_platforms: true,
+                ..Default::default()
+            },
         )
         .expect("solid floors remain collidable while passing down");
 
         assert_eq!(collision.line_id.polygon, 0);
         assert_eq!(collision.hit_position, FGVec2::lit("0", "0"));
     }
+
+    #[test]
+    fn upward_bottom_crossing_can_land_on_soft_platform() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![horizontal_platform("0")],
+            ..Default::default()
+        };
+        let previous_translation = FighterPreviousTranslation(FGVec2::lit("0", "-1"));
+        let mut translation = FighterTranslation(FGVec2::lit("0", "1"));
+        let mut velocity = FighterVelocity(FGVec2::lit("0", "2"));
+        let mut ecb = FighterECB::default();
+        let desired = FighterDesiredECB::from(ecb);
+
+        let collision = air_collide_with_stage_substepped(
+            &previous_translation,
+            &mut translation,
+            &mut velocity,
+            &mut ecb,
+            &desired,
+            &stage_collision,
+            &[],
+            AirCollisionOptions {
+                land_on_soft_platforms_from_below: true,
+                ..Default::default()
+            },
+        )
+        .expect("the upward bottom-point crossing should land on the platform");
+
+        assert_eq!(collision.hit_position, FGVec2::ZERO);
+        assert_eq!(collision.line_id, StageLineID { polygon: 0, segment: 0 });
+        assert_eq!(translation.0, FGVec2::ZERO);
+        assert_eq!(velocity.y, FGi32::ZERO);
+    }
+
+    #[test]
+    fn upward_platform_landing_requires_crossing_and_opt_in() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![horizontal_platform("0")],
+            ..Default::default()
+        };
+        let previous_ecb = FighterPreviousECB::default();
+        let ecb = FighterECB::default();
+        let options = AirCollisionOptions {
+            land_on_soft_platforms_from_below: true,
+            ..Default::default()
+        };
+
+        assert!(
+            air_collide_with_stage(
+                &FighterPreviousTranslation(FGVec2::lit("0", "-2")),
+                &FighterTranslation(FGVec2::lit("0", "-1")),
+                &previous_ecb,
+                &ecb,
+                &stage_collision,
+                &[],
+                options,
+            )
+            .is_none()
+        );
+        assert!(
+            air_collide_with_stage(
+                &FighterPreviousTranslation(FGVec2::lit("0", "-1")),
+                &FighterTranslation(FGVec2::lit("0", "1")),
+                &previous_ecb,
+                &ecb,
+                &stage_collision,
+                &[],
+                Default::default(),
+            )
+            .is_none()
+        );
+    }
+
+    #[test]
+    fn upward_crossing_does_not_land_on_solid_or_ignored_platforms() {
+        let previous_translation = FighterPreviousTranslation(FGVec2::lit("0", "-1"));
+        let translation = FighterTranslation(FGVec2::lit("0", "1"));
+        let previous_ecb = FighterPreviousECB::default();
+        let ecb = FighterECB::default();
+        let options = AirCollisionOptions {
+            land_on_soft_platforms_from_below: true,
+            ..Default::default()
+        };
+        let solid_stage = StageCollision {
+            stage_polys: vec![solid_floor()],
+            ..Default::default()
+        };
+        let platform_stage = StageCollision {
+            stage_polys: vec![horizontal_platform("0")],
+            ..Default::default()
+        };
+
+        assert!(
+            air_collide_with_stage(
+                &previous_translation,
+                &translation,
+                &previous_ecb,
+                &ecb,
+                &solid_stage,
+                &[],
+                options,
+            )
+            .is_none()
+        );
+        assert!(
+            air_collide_with_stage(
+                &previous_translation,
+                &translation,
+                &previous_ecb,
+                &ecb,
+                &platform_stage,
+                &[0],
+                options,
+            )
+            .is_none()
+        );
+    }
 }

src/fighter/ecb.rs

@@ -4,14 +4,12 @@ use crate::{
     fighter::{
         FighterFacingDirection, FighterSurfaceState, FighterTranslation,
         baked_animation::FighterBoneMatrices,
-    }, math::{int::FGi32, vec::FGVec2},
+    },
+    math::{int::FGi32, vec::FGVec2},
 };
 
-/// Environment collision box: the diamond used to resolve a fighter against
-/// the stage. Purely geometry — the collision response lives in
-/// [`super::collision`].
 #[derive(Component, Debug, Clone, Copy, Hash, Default)]
-#[require(FighterPreviousECB)]
+#[require(FighterPreviousECB, FighterDesiredECB)]
 pub struct FighterECB {
     pub top: FGVec2,
     pub bottom: FGVec2,
@@ -19,6 +17,14 @@ pub struct FighterECB {
     pub right: FGVec2,
 }
 
+#[derive(Component, Debug, Clone, Copy, Hash, Default)]
+pub struct FighterDesiredECB {
+    pub top: FGVec2,
+    pub bottom: FGVec2,
+    pub left: FGVec2,
+    pub right: FGVec2,
+}
+
 #[derive(Component, Debug, Clone)]
 pub struct FighterECBBoneIndices {
     pub indices: Vec<usize>,
@@ -43,12 +49,96 @@ impl From<FighterECB> for FighterPreviousECB {
     }
 }
 
+impl From<FighterECB> for FighterDesiredECB {
+    fn from(ecb: FighterECB) -> Self {
+        Self {
+            top: ecb.top,
+            bottom: ecb.bottom,
+            left: ecb.left,
+            right: ecb.right,
+        }
+    }
+}
+
+impl FighterDesiredECB {
+    pub fn as_ecb(self) -> FighterECB {
+        FighterECB {
+            top: self.top,
+            bottom: self.bottom,
+            left: self.left,
+            right: self.right,
+        }
+    }
+
+    pub fn validate(&mut self) {
+        let minimum = FGi32::lit("1.0");
+        if (self.top.y - self.bottom.y).abs() < minimum {
+            self.top.y += minimum;
+            let midpoint = (self.top.y + self.bottom.y) / FGi32::lit("2.0");
+            self.left.y = midpoint;
+            self.right.y = midpoint;
+        }
+        if self.top.y < minimum {
+            self.top.y = minimum;
+        }
+        if self.left.x > -minimum {
+            self.left.x = -minimum;
+        }
+        if self.right.x < minimum {
+            self.right.x = minimum;
+        }
+        if self.top.y < self.bottom.y {
+            self.top.y = self.bottom.y + minimum;
+        }
+
+        let midpoint = (self.top.y + self.bottom.y) / FGi32::lit("2.0");
+        if self.left.y < self.bottom.y || self.left.y > self.top.y {
+            self.left.y = midpoint;
+        }
+        if self.right.y < self.bottom.y || self.right.y > self.top.y {
+            self.left.y = midpoint;
+            self.right.y = midpoint;
+        }
+        let epsilon = FGi32::from_bits(66);
+        if self.top.y - self.right.y < epsilon
+            || self.right.y - self.bottom.y < epsilon
+        {
+            self.right.y = midpoint;
+        }
+        if self.top.y - self.left.y < epsilon
+            || self.left.y - self.bottom.y < epsilon
+        {
+            self.left.y = midpoint;
+        }
+    }
+}
+
 pub fn snapshot_fighter_ecb(fighters: Query<(&FighterECB, &mut FighterPreviousECB)>) {
     for (ecb, mut previous_ecb) in fighters {
         *previous_ecb = (*ecb).into();
     }
 }
 
+pub fn interpolate_ecb(ecb: &mut FighterECB, desired: FighterDesiredECB, time: FGi32) {
+    let lerp = |a: FGVec2, b: FGVec2| a + (b - a) * time;
+    ecb.top = lerp(ecb.top, desired.top);
+    ecb.bottom = lerp(ecb.bottom, desired.bottom);
+    ecb.left = lerp(ecb.left, desired.left);
+    ecb.right = lerp(ecb.right, desired.right);
+}
+
+pub fn ecb_max_delta(ecb: &FighterECB, desired: &FighterDesiredECB) -> FGi32 {
+    [
+        (desired.left.x - ecb.left.x).abs(),
+        (desired.right.x - ecb.right.x).abs(),
+        (desired.top.y - ecb.top.y).abs(),
+        (desired.right.y - ecb.right.y).abs(),
+    ]
+    .into_iter()
+    .max()
+    .unwrap_or(FGi32::ZERO)
+}
+
 impl FighterECB {
     pub fn to_3d_lineloop(&self, trf: Transform) -> [Vec3; 4] {
         [self.top, self.right, self.bottom, self.left]
@@ -58,6 +148,17 @@ impl FighterECB {
     pub fn get_bottom_point(&self) -> FGVec2 {
         self.bottom
     }
+
+    /// Change the local origin to the bottom point without moving the ECB in
+    /// world space. Grounded fighters use the floor contact as their origin.
+    pub fn rebase_onto_bottom(&mut self) -> FGVec2 {
+        let bottom = self.bottom;
+        self.top -= bottom;
+        self.left -= bottom;
+        self.right -= bottom;
+        self.bottom = FGVec2::ZERO;
+        bottom
+    }
 }
 
 impl FighterPreviousECB {
@@ -73,7 +174,7 @@ impl FighterPreviousECB {
 
 pub fn update_ecb(
     query: Query<(
-        &mut FighterECB,
+        &mut FighterDesiredECB,
         &FighterSurfaceState,
         &FighterECBBoneIndices,
         &FighterBoneMatrices,
@@ -81,23 +182,44 @@ pub fn update_ecb(
         &FighterFacingDirection,
     )>,
 ) {
-    for (mut ecb, surface_state, bone_indices, bone_matrices, translation, facing_dir) in query {
+    for (mut desired, surface_state, bone_indices, bone_matrices, translation, facing_dir) in query
+    {
         let trf = translation.get_3d_transform(facing_dir);
 
-        let transformed_ecb_bones = bone_indices.indices.iter().filter_map(|idx| {
+        let transformed_ecb_bones = bone_indices
-            let Some((_, bone_matrix)) = bone_matrices.get_by_idx(*idx) else {
+            .indices
-                return None;
+            .iter()
-            };
+            .filter_map(|idx| {
+                let Some((_, bone_matrix)) = bone_matrices.get_by_idx(*idx) else {
+                    return None;
+                };
 
-            let pt = trf.transform_point(bone_matrix.get_translation());
+                let pt = trf.transform_point(bone_matrix.get_translation());
 
-            Some(FGVec2::new(pt.x, pt.y) - translation.0)
+                Some(FGVec2::new(pt.x, pt.y) - translation.0)
-        }).collect::<Vec<_>>();
+            })
+            .collect::<Vec<_>>();
 
-        let max_x = transformed_ecb_bones.iter().max_by(|a, b| a.x.cmp(&b.x)).map(|final_val| final_val.x).unwrap_or(FGi32::lit("0.5"));
+        let max_x = transformed_ecb_bones
-        let min_x = transformed_ecb_bones.iter().min_by(|a, b| a.x.cmp(&b.x)).map(|final_val| final_val.x).unwrap_or(FGi32::lit("-0.5"));
+            .iter()
-        let max_y = transformed_ecb_bones.iter().max_by(|a, b| a.y.cmp(&b.y)).map(|final_val| final_val.y).unwrap_or(FGi32::lit("0.5"));
+            .max_by(|a, b| a.x.cmp(&b.x))
-        let min_y = transformed_ecb_bones.iter().min_by(|a, b| a.y.cmp(&b.y)).map(|final_val| final_val.y).unwrap_or(FGi32::lit("-0.5"));
+            .map(|final_val| final_val.x)
+            .unwrap_or(FGi32::lit("0.5"));
+        let min_x = transformed_ecb_bones
+            .iter()
+            .min_by(|a, b| a.x.cmp(&b.x))
+            .map(|final_val| final_val.x)
+            .unwrap_or(FGi32::lit("-0.5"));
+        let max_y = transformed_ecb_bones
+            .iter()
+            .max_by(|a, b| a.y.cmp(&b.y))
+            .map(|final_val| final_val.y)
+            .unwrap_or(FGi32::lit("0.5"));
+        let min_y = transformed_ecb_bones
+            .iter()
+            .min_by(|a, b| a.y.cmp(&b.y))
+            .map(|final_val| final_val.y)
+            .unwrap_or(FGi32::lit("-0.5"));
 
         let midpoint_height = (max_y + min_y) / FGi32::lit("2.0");
         let top = FGVec2::new(FGi32::ZERO, max_y);
@@ -105,24 +227,29 @@ pub fn update_ecb(
         let left = FGVec2::new(min_x, midpoint_height);
         let right = FGVec2::new(max_x, midpoint_height);
 
-        let ecb_lock_frames_remaining = if let FighterSurfaceState::Airborne { ecb_lock_frames_remaining, .. } = surface_state {
+        let ecb_lock_frames_remaining = if let FighterSurfaceState::Airborne {
+            ecb_lock_frames_remaining,
+            ..
+        } = surface_state
+        {
             *ecb_lock_frames_remaining
         } else {
             0
         };
 
-        ecb.top = top;
+        desired.top = top;
 
         if ecb_lock_frames_remaining == 0 {
-            ecb.bottom = bottom;
+            desired.bottom = bottom;
         }
 
-        ecb.left = left;
+        desired.left = left;
-        ecb.right = right;
+        desired.right = right;
 
         if surface_state.is_grounded() {
-            ecb.bottom = FGVec2::ZERO;
+            desired.bottom = FGVec2::ZERO;
         }
+        desired.validate();
     }
 }
 
@@ -152,4 +279,60 @@ mod tests {
         assert_eq!(previous.left, current.left);
         assert_eq!(previous.right, current.right);
     }
+
+    #[test]
+    fn interpolation_reaches_target_with_full_step() {
+        let mut current = FighterECB {
+            top: FGVec2::lit("0", "1"),
+            bottom: FGVec2::lit("0", "0"),
+            left: FGVec2::lit("-1", "0.5"),
+            right: FGVec2::lit("1", "0.5"),
+        };
+        let desired = FighterDesiredECB {
+            top: FGVec2::lit("0", "3"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-2", "1"),
+            right: FGVec2::lit("2", "1"),
+        };
+        interpolate_ecb(&mut current, desired, FGi32::ONE);
+        assert_eq!(current.top, desired.top);
+        assert_eq!(current.bottom, desired.bottom);
+        assert_eq!(current.left, desired.left);
+        assert_eq!(current.right, desired.right);
+    }
+
+    #[test]
+    fn validation_repairs_tiny_and_out_of_range_diamond() {
+        let mut desired = FighterDesiredECB {
+            top: FGVec2::lit("0", "0.25"),
+            bottom: FGVec2::lit("0", "0"),
+            left: FGVec2::lit("0", "4"),
+            right: FGVec2::lit("0", "-4"),
+        };
+        desired.validate();
+
+        assert_eq!(desired.top.y, FGi32::lit("1.25"));
+        assert_eq!(desired.left.x, FGi32::lit("-1"));
+        assert_eq!(desired.right.x, FGi32::lit("1"));
+        assert_eq!(desired.left.y, FGi32::lit("0.625"));
+        assert_eq!(desired.right.y, FGi32::lit("0.625"));
+    }
+
+    #[test]
+    fn rebasing_onto_bottom_preserves_world_points() {
+        let origin = FGVec2::lit("4", "8");
+        let mut ecb = FighterECB {
+            top: FGVec2::lit("0", "3"),
+            bottom: FGVec2::lit("0", "-1"),
+            left: FGVec2::lit("-2", "1"),
+            right: FGVec2::lit("2", "1"),
+        };
+        let old_world_points = [ecb.top, ecb.bottom, ecb.left, ecb.right].map(|p| origin + p);
+        let new_origin = origin + ecb.bottom;
+        ecb.rebase_onto_bottom();
+        let new_world_points = [ecb.top, ecb.bottom, ecb.left, ecb.right].map(|p| new_origin + p);
+
+        assert_eq!(old_world_points, new_world_points);
+        assert_eq!(ecb.bottom, FGVec2::ZERO);
+    }
 }

src/fighter/mod.rs

@@ -10,6 +10,7 @@ pub mod animation;
 pub mod attack;
 pub mod attributes;
 pub mod baked_animation;
+pub mod blast_zones;
 pub mod collision;
 pub mod debug;
 pub mod ecb;
@@ -21,7 +22,6 @@ pub mod push;
 pub mod state;
 pub mod surface;
 pub mod visual;
-pub mod blast_zones;
 
 // The fighter components are re-exported so the rest of the crate can say
 // `fighter::FighterVelocity` without caring which file it lives in. Named
@@ -37,13 +37,25 @@ pub use motion::{
 pub use surface::FighterSurfaceState;
 
 use crate::{
-    AppState, fighter::{
+    AppState,
+    fighter::{
         attack::{
             AttackKind, FighterAttackPlugin, FighterAttackScriptAssets, FighterDamage,
-            FighterKnockbackVelocity, FighterPendingHitReaction, FighterSolvedHurtboxes,
+            FighterKnockbackState, FighterKnockbackVelocity, FighterPendingHitReaction,
-            FighterStaleMoveQueue,
+            FighterSolvedHurtboxes, FighterStaleMoveQueue,
-        }, baked_animation::FighterBoneIndexMap, ecb::FighterECBBoneIndices, manifest::FighterManifest, state::{FighterState, air::AirborneStateCommon, fall::FallState}, visual::{FighterAnimations, FighterInvulnerabilityVisualState},
+        },
-    }, game_settings::GameSettings, input::FighterInput, math::{int::FGi32, vec::FGVec2}, player::Player, schedule::GameplaySet, scripting::FighterAttackScript,
+        baked_animation::FighterBoneIndexMap,
+        ecb::{FighterDesiredECB, FighterECBBoneIndices},
+        manifest::FighterManifest,
+        state::{FighterState, air::AirborneStateCommon, fall::FallState},
+        visual::{FighterAnimations, FighterInvulnerabilityVisualState},
+    },
+    game_settings::GameSettings,
+    input::FighterInput,
+    math::{int::FGi32, vec::FGVec2},
+    player::Player,
+    schedule::GameplaySet,
+    scripting::FighterAttackScript,
 };
 use state::state_interrupt_system;
 
@@ -102,7 +114,8 @@ impl FighterLedgeInformation {
     }
 
     fn tick(&mut self) {
-        self.regrab_lockout_remaining_frames = self.regrab_lockout_remaining_frames.saturating_sub(1);
+        self.regrab_lockout_remaining_frames =
+            self.regrab_lockout_remaining_frames.saturating_sub(1);
     }
 }
 
@@ -135,8 +148,12 @@ mod ledge_grab_lockout_tests {
 pub enum FighterInvulnerabilityState {
     #[default]
     Vulnerable,
-    Invulnerable { frames_remaining: Option<u32> },
+    Invulnerable {
-    Intangible { frames_remaining: Option<u32> }
+        frames_remaining: Option<u32>,
+    },
+    Intangible {
+        frames_remaining: Option<u32>,
+    },
 }
 
 impl FighterFacingDirection {
@@ -195,9 +212,10 @@ pub struct FighterPendingRespawn(bool);
     FighterHitstop,
     FighterLedgeInformation,
     FighterKnockbackVelocity,
+    FighterKnockbackState,
     FighterTranslation,
     FighterInvulnerabilityState,
-    FighterInvulnerabilityVisualState,
+    FighterInvulnerabilityVisualState
 )]
 pub struct Fighter {
     pub manifest: Handle<FighterManifest>,
@@ -226,7 +244,10 @@ impl Plugin for FighterPlugin {
             )
             .add_systems(
                 GgrsSchedule,
-                (state::state_update_system, decay_hitstop, decay_invulnerability)
+                (
+                    state::state_update_system,
+                    decay_invulnerability,
+                )
                     .chain()
                     .in_set(GameplaySet::StateUpdate),
             )
@@ -241,11 +262,14 @@ impl Plugin for FighterPlugin {
                 (
                     (
                         blast_zones::apply_blast_zones,
-                        ecb::update_ecb,
                         ecb::decrement_ecb_lockout,
+                        ecb::update_ecb,
                         state::state_collision_interrupt_system,
+                        // Every gameplay phase must observe the same hitstop value.
+                        decay_hitstop,
                         decay_ledge_grab_lockout,
-                    ).chain(),
+                    )
+                        .chain(),
                     baked_animation::resample_fighter_bone_matrices,
                 )
                     .chain()
@@ -272,6 +296,8 @@ impl Plugin for FighterPlugin {
             // is a desync waiting to happen.
             .rollback_component_with_copy::<FighterECB>()
             .checksum_component_with_hash::<FighterECB>()
+            .rollback_component_with_copy::<FighterDesiredECB>()
+            .checksum_component_with_hash::<FighterDesiredECB>()
             .rollback_component_with_clone::<FighterStaleMoveQueue>()
             .checksum_component_with_hash::<FighterStaleMoveQueue>()
             .rollback_component_with_copy::<ecb::FighterPreviousECB>()
@@ -305,6 +331,8 @@ impl Plugin for FighterPlugin {
             .checksum_component_with_hash::<FighterInvulnerabilityState>()
             .rollback_component_with_copy::<FighterKnockbackVelocity>()
             .checksum_component_with_hash::<FighterKnockbackVelocity>()
+            .rollback_component_with_copy::<FighterKnockbackState>()
+            .checksum_component_with_hash::<FighterKnockbackState>()
             .rollback_component_with_clone::<baked_animation::FighterBoneMatrices>()
             .checksum_component_with_hash::<baked_animation::FighterBoneMatrices>()
             // Debug views.
@@ -335,8 +363,9 @@ impl Plugin for FighterPlugin {
                     .run_if(crate::debug_tools::attack_hitboxes_enabled)
                     .run_if(in_state(AppState::InMatch)),
             )
-            .add_systems(FixedPostUpdate, 
+            .add_systems(
-                visual::update_status_colors.run_if(resource_exists::<GameSettings>)
+                FixedPostUpdate,
+                visual::update_status_colors.run_if(resource_exists::<GameSettings>),
             )
             .add_systems(
                 FixedPostUpdate,
@@ -396,10 +425,11 @@ pub fn spawn_fighter(
             Transform::from_scale(Vec3::splat(model_scale.to_num())),
             (
                 FighterECB::default(),
+                FighterDesiredECB::default(),
                 FighterHitboxes::default(),
                 FighterECBBoneIndices {
-                    indices: ecb_bone_indices
+                    indices: ecb_bone_indices,
-                }
+                },
             ),
             (
                 FighterVelocity::default(),
@@ -449,7 +479,7 @@ pub fn decay_invulnerability(query: Query<&mut FighterInvulnerabilityState>) {
                 } else {
                     None
                 }
-            },
+            }
             FighterInvulnerabilityState::Intangible { frames_remaining } => {
                 if let Some(frames_remaining) = frames_remaining {
                     *frames_remaining = frames_remaining.saturating_sub(1);
@@ -457,7 +487,7 @@ pub fn decay_invulnerability(query: Query<&mut FighterInvulnerabilityState>) {
                 } else {
                     None
                 }
-            },
+            }
         };
 
         if let Some(frames_remaining) = frames_remaining {

src/fighter/state/air.rs

@@ -93,6 +93,19 @@ pub fn apply_air_motion(
     translation.0 += velocity.0;
 }
 
+/// Applies ordinary and launch velocity together, then advances launch decay.
+/// Hitstop skips state updates entirely, so neither decay nor launch age moves
+/// while the fighter is frozen.
+pub fn apply_air_motion_with_knockback(ctx: &mut crate::fighter::state::UpdateContext) {
+    let combined_velocity = FighterVelocity(ctx.velocity.0 + ctx.knockback_velocity.0);
+    apply_air_motion(&combined_velocity, ctx.translation, ctx.prev_translation);
+    attack::decay_knockback(
+        ctx.knockback_velocity,
+        ctx.knockback_state,
+        ctx.game_settings.fighter_common.knockback_decay_per_frame,
+    );
+}
+
 pub fn update_standard_motion(
     ctx: &mut crate::fighter::state::UpdateContext,
     airborne_common: &mut AirborneStateCommon,
@@ -109,7 +122,7 @@ pub fn update_standard_motion(
         airborne_common.is_fast_falling,
     );
     apply_air_drift(ctx.velocity, ctx.fighter_attributes, ctx.input);
-    apply_air_motion(ctx.velocity, ctx.translation, ctx.prev_translation);
+    apply_air_motion_with_knockback(ctx);
 }
 
 pub fn air_interrupts_common(
@@ -125,23 +138,24 @@ pub fn air_interrupts_common(
 pub fn collision_interrupt(
     ctx: &mut CollisionContext,
     landing_type: LandingType,
-    can_ignore_soft_platforms: bool,
+    options: crate::fighter::collision::AirCollisionOptions,
 ) -> Option<FighterState> {
     if ctx.velocity.y <= FGi32::ZERO {
         if let Some(ledge_result) = ctx.air_collide_with_ledges() {
+            ctx.apply_desired_ecb();
             return Some(FighterState::LedgeGrab(LedgeGrabState::new(ledge_result.ledge)));
         }
     }
 
-    let res = ctx.air_collide_with_stage(can_ignore_soft_platforms)?;
+    let res = ctx.air_collide_with_stage(options)?;
-    let diff = res.hit_position - ctx.translation.0;
+    ctx.translation.0 = res.resolved_translation;
-    ctx.ecb.bottom -= diff;
+    let bottom_offset = ctx.ecb.rebase_onto_bottom();
-    ctx.ecb.top -= diff;
+    ctx.translation.0 += bottom_offset;
-    ctx.ecb.left -= diff;
+    *ctx.desired_ecb = crate::fighter::ecb::FighterDesiredECB::from(*ctx.ecb);
-    ctx.ecb.right -= diff;
-    ctx.translation.0 = res.hit_position;
     ctx.presentation_snap.0 = true;
     ctx.surface.land(res.line_id, ctx.ledge_info);
+    ctx.knockback_velocity.0 = FGVec2::ZERO;
+    ctx.knockback_state.clear();
     Some(FighterState::Land(LandingState::create(landing_type)))
 }
 

src/fighter/state/air_attack.rs

@@ -93,7 +93,7 @@ impl FighterStateImpl for AirAttackState {
         let coll_interrupt = air::collision_interrupt(
             state_context,
             crate::fighter::state::land::LandingType::Normal,
-            false,
+            Default::default(),
         );
 
         coll_interrupt.map(|state| {

src/fighter/state/air_dodge.rs

@@ -1,17 +1,9 @@
 use crate::{
     fighter::{
-        FighterInvulnerabilityState,
+        FighterInvulnerabilityState, animation::AnimKind, state::{
-        animation::AnimKind,
+            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext, UpdateContext, air::{self, AirborneStateCommon}, fall::FallState, land::{LandingState, LandingType},
-        state::{
-            CollisionContext, EnterContext, FighterState, FighterStateImpl, InterruptContext,
-            UpdateContext,
-            air::{self, AirborneStateCommon},
-            fall::FallState,
-            land::LandingType,
         },
-    },
+    }, input, math::vec::FGVec2, stage::line::{StageLineID, StagePolyLineSegmentType},
-    input,
-    math::vec::FGVec2,
 };
 
 #[derive(Debug, Clone, Hash)]
@@ -41,18 +33,44 @@ impl FighterStateImpl for AirDodgeState {
         }
         state_context.velocity.0 *= state_context.fighter_attributes.air_dodge_decay;
 
-        air::apply_air_motion(
+        air::apply_air_motion_with_knockback(state_context);
-            state_context.velocity,
-            state_context.translation,
-            state_context.prev_translation,
-        );
     }
 
     fn check_collision_interrupt(
         &mut self,
         state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
-        air::collision_interrupt(state_context, LandingType::Special, false)
+        let can_wavesnap = self.direction.y.is_zero() || self.direction.y.is_negative();
+        
+        if can_wavesnap {
+            for (poly_idx, poly) in state_context.stage_collision.stage_polys.iter().enumerate() {
+                for (segment_idx, segment) in poly.segments.iter().enumerate() {
+                    if !matches!(segment.segment_type, StagePolyLineSegmentType::Floor) {
+                        continue;
+                    }
+                    let bottom_point = state_context.translation.0 + state_context.ecb.get_bottom_point();
+                    let point_in_segment = segment.segment.closest_point(bottom_point);
+                    let dist_to_segment = point_in_segment.distance(bottom_point);
+                    if dist_to_segment <= state_context.waveland_snap_distance {
+                        state_context.ecb.bottom = point_in_segment - state_context.translation.0;
+                        state_context.ecb.rebase_onto_bottom();
+                        state_context.surface.land(StageLineID { polygon: poly_idx, segment: segment_idx }, state_context.ledge_info);
+                        state_context.knockback_velocity.0 = FGVec2::ZERO;
+                        state_context.knockback_state.clear();
+                        return Some(FighterState::Land(LandingState::create(LandingType::Special)));
+                    }
+                }
+            }
+        }
+
+        air::collision_interrupt(
+            state_context,
+            LandingType::Special,
+            crate::fighter::collision::AirCollisionOptions {
+                land_on_soft_platforms_from_below: true,
+                ..Default::default()
+            },
+        )
     }
 
     fn on_enter(&mut self, state_context: &mut EnterContext) {

src/fighter/state/angel.rs

@@ -43,12 +43,13 @@ impl FighterStateImpl for AngelState {
     
     fn check_collision_interrupt(
         &mut self,
-        _state_context: &mut super::CollisionContext,
+        state_context: &mut super::CollisionContext,
     ) -> Option<super::FighterState> {
+        state_context.apply_desired_ecb();
         None
     }
     
     fn surface_policy(&self) -> super::SurfacePolicy {
         super::SurfacePolicy::Airborne(crate::fighter::surface::EcbLockPolicy::Clear)
     }
-}
+}

src/fighter/state/fall.rs

@@ -39,7 +39,10 @@ impl FighterStateImpl for FallState {
         air::collision_interrupt(
             state_context,
             crate::fighter::state::land::LandingType::Normal,
-            true,
+            crate::fighter::collision::AirCollisionOptions {
+                can_pass_through_soft_platforms: true,
+                ..Default::default()
+            },
         )
     }
     

src/fighter/state/ground.rs

@@ -4,16 +4,18 @@
 
 use crate::fighter::state::air_dodge::AirDodgeState;
 use crate::fighter::state::{
-    CollisionContext, FighterState, InterruptContext, air, crouch, dash, fall, ground_attack, turn, wait, walk,
+    CollisionContext, FighterState, InterruptContext, air, crouch, dash, fall, ground_attack, turn,
-};
+    wait, walk,
-use crate::fighter::{
-    FighterAttributes, FighterTranslation, FighterVelocity,
 };
+use crate::fighter::{collision, ecb};
+use crate::fighter::{FighterAttributes, FighterTranslation, FighterVelocity};
 use crate::game_settings::GameSettings;
 use crate::input::FighterInput;
 use crate::math::int::{FGWide, FGi32};
 use crate::math::vec::FGVec2;
-use crate::stage::line::{StageLineID, StagePoly, StagePolyLineSegment, StagePolyLineSegmentType};
+use crate::stage::line::{StagePoly, StagePolyLineSegment, StagePolyLineSegmentType};
+#[cfg(test)]
+use crate::stage::line::StageLineID;
 
 pub fn apply_grounded_friction(friction: FGi32, ground_vel: FGi32) -> FGi32 {
     if friction.abs() > ground_vel.abs() {
@@ -148,10 +150,7 @@ fn resolve_grounded_position(
     GroundedPositionResult::InAir
 }
 
-pub fn apply_grounded_motion(
+pub fn apply_grounded_motion(velocity: &FighterVelocity, translation: &mut FighterTranslation) {
-    velocity: &FighterVelocity,
-    translation: &mut FighterTranslation,
-) {
     // Vertical velocity should be 0 on the ground
     translation.0 += FGVec2::new(velocity.0.x, FGi32::ZERO);
 }
@@ -176,61 +175,77 @@ pub fn collide_with_stage_grounded(
     state_context: &mut CollisionContext,
     can_walk_off: bool,
 ) -> GroundedMotionResult {
-    let translation = &mut state_context.translation;
+    let Some(mut line_id) = state_context.surface.line_id() else {
-    let ecb = &state_context.ecb;
+        state_context.apply_desired_ecb();
-    let stage_collision = state_context.stage_collision;
-
-    let Some(current_line_id) = state_context.surface.line_id() else {
         return GroundedMotionResult::InAir;
     };
+    let requested_translation = state_context.translation.0;
+    let movement = requested_translation - state_context.prev_translation.0;
+    let largest_change = movement
+        .x
+        .abs()
+        .max(movement.y.abs())
+        .max(ecb::ecb_max_delta(state_context.ecb, state_context.desired_ecb));
+    let steps = collision::collision_step_count(largest_change);
+    let movement_per_step = movement / FGi32::from_num(steps);
+    let mut current_position = state_context.prev_translation.0;
+    let mut current_ecb = *state_context.ecb;
 
-    let stage_poly = stage_collision.stage_polys.get(current_line_id.polygon);
+    for step in 0..steps {
+        ecb::interpolate_ecb(
+            &mut current_ecb,
+            *state_context.desired_ecb,
+            FGi32::ONE / FGi32::from_num(steps - step),
+        );
+        current_position = if step + 1 == steps {
+            requested_translation
+        } else {
+            state_context.prev_translation.0
+                + movement_per_step * FGi32::from_num(step + 1)
+        };
 
-    if let Some(stage_poly) = stage_poly {
+        let Some(stage_poly) = state_context.stage_collision.stage_polys.get(line_id.polygon) else {
-        let ecb_bottom_pos = translation.0 + ecb.get_bottom_point();
+            *state_context.ecb = current_ecb;
+            state_context.translation.0 = current_position;
+            state_context.surface.apply_airborne_policy(
+                crate::fighter::surface::EcbLockPolicy::StartOnDetach,
+                state_context.leave_ground_ecb_lock_duration,
+            );
+            return GroundedMotionResult::InAir;
+        };
         match resolve_grounded_position(
             stage_poly,
-            current_line_id.segment,
+            line_id.segment,
-            ecb_bottom_pos,
+            current_position + current_ecb.bottom,
             can_walk_off,
         ) {
-            GroundedPositionResult::InGround {
+            GroundedPositionResult::InGround { point, segment_idx, blocked } => {
-                point,
+                line_id.segment = segment_idx;
-                segment_idx,
+                current_position = point - current_ecb.bottom;
-                blocked,
+                let segment = stage_poly.get_segment(segment_idx).unwrap();
-            } => {
-                let current_segment = stage_poly.get_segment(segment_idx).unwrap();
-                translation.0 = point - ecb.get_bottom_point();
                 state_context.velocity.0 = if blocked {
                     FGVec2::ZERO
                 } else {
                     state_context.velocity.0
-                        - state_context
+                        - state_context.velocity.0.project_onto_normalized(segment.normal)
-                            .velocity
-                            .0
-                            .project_onto_normalized(current_segment.normal)
                 };
-                state_context.surface.land(StageLineID {
-                    polygon: current_line_id.polygon,
-                    segment: segment_idx,
-                }, state_context.ledge_info);
-                GroundedMotionResult::InGround
             }
             GroundedPositionResult::InAir => {
+                *state_context.ecb = current_ecb;
+                state_context.translation.0 = current_position;
                 state_context.surface.apply_airborne_policy(
                     crate::fighter::surface::EcbLockPolicy::StartOnDetach,
                     state_context.leave_ground_ecb_lock_duration,
                 );
-                GroundedMotionResult::InAir
+                return GroundedMotionResult::InAir;
             }
         }
-    } else {
-        state_context.surface.apply_airborne_policy(
-            crate::fighter::surface::EcbLockPolicy::StartOnDetach,
-            state_context.leave_ground_ecb_lock_duration,
-        );
-        GroundedMotionResult::InAir
     }
+
+    *state_context.ecb = current_ecb;
+    state_context.translation.0 = current_position;
+    state_context.surface.land(line_id, state_context.ledge_info);
+    GroundedMotionResult::InGround
 }
 
 pub fn collision_interrupt(ctx: &mut CollisionContext, can_walk_off: bool) -> Option<FighterState> {
@@ -245,11 +260,14 @@ pub fn collision_interrupt(ctx: &mut CollisionContext, can_walk_off: bool) -> Op
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::fighter::ecb::FighterPreviousECB;
+    use crate::fighter::attack::{FighterKnockbackState, FighterKnockbackVelocity};
-    use crate::fighter::{FighterECB, FighterLedgeInformation, FighterPreviousTranslation, FighterSurfaceState};
+    use crate::fighter::ecb::{FighterDesiredECB, FighterPreviousECB};
-    use crate::math::rect::FGRect;
+    use crate::fighter::{
-use crate::stage::line::StagePolyType;
+        FighterECB, FighterLedgeInformation, FighterPreviousTranslation, FighterSurfaceState,
+    };
     use crate::input::FighterInput;
+    use crate::math::rect::FGRect;
+    use crate::stage::line::StagePolyType;
 
     fn two_segment_floor() -> StagePoly {
         StagePoly::build(
@@ -371,6 +389,8 @@ use crate::stage::line::StagePolyType;
         let mut translation = FighterTranslation(FGVec2::lit("11", "0"));
         let previous_translation = FighterPreviousTranslation(translation.0);
         let mut velocity = FighterVelocity::default();
+        let mut knockback_velocity = FighterKnockbackVelocity::default();
+        let mut knockback_state = FighterKnockbackState::default();
         let mut ledge_info = FighterLedgeInformation::default();
         let mut ecb = FighterECB {
             bottom: FGVec2::lit("0.0", "-0.5"),
@@ -379,14 +399,18 @@ use crate::stage::line::StagePolyType;
             right: FGVec2::lit("0.5", "0.0"),
         };
         let previous_ecb = FighterPreviousECB::from(ecb);
+        let mut desired_ecb = FighterDesiredECB::from(ecb);
         let mut presentation_snap = crate::fighter::FighterPresentationSnap::default();
         let mut context = CollisionContext {
             translation: &mut translation,
             prev_translation: &previous_translation,
             input: &FighterInput::default(),
             velocity: &mut velocity,
+            knockback_velocity: &mut knockback_velocity,
+            knockback_state: &mut knockback_state,
             surface: &mut surface,
             ecb: &mut ecb,
+            desired_ecb: &mut desired_ecb,
             ledge_info: &mut ledge_info,
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
@@ -397,6 +421,7 @@ use crate::stage::line::StagePolyType;
                 origin: FGVec2::ZERO,
                 end: FGVec2::ZERO,
             },
+            waveland_snap_distance: FGi32::ZERO,
         };
 
         assert!(matches!(
@@ -433,6 +458,8 @@ use crate::stage::line::StagePolyType;
         let mut translation = FighterTranslation(FGVec2::lit("11", "0"));
         let previous_translation = FighterPreviousTranslation(translation.0);
         let mut velocity = FighterVelocity::default();
+        let mut knockback_velocity = FighterKnockbackVelocity::default();
+        let mut knockback_state = FighterKnockbackState::default();
         let mut ecb = FighterECB {
             bottom: FGVec2::lit("0.0", "-0.5"),
             top: FGVec2::lit("0.0", "0.5"),
@@ -440,6 +467,7 @@ use crate::stage::line::StagePolyType;
             right: FGVec2::lit("0.5", "0.0"),
         };
         let previous_ecb = FighterPreviousECB::from(ecb);
+        let mut desired_ecb = FighterDesiredECB::from(ecb);
         let mut presentation_snap = crate::fighter::FighterPresentationSnap::default();
         let mut ledge_info = FighterLedgeInformation::default();
         let mut context = CollisionContext {
@@ -447,8 +475,11 @@ use crate::stage::line::StagePolyType;
             prev_translation: &previous_translation,
             input: &FighterInput::default(),
             velocity: &mut velocity,
+            knockback_velocity: &mut knockback_velocity,
+            knockback_state: &mut knockback_state,
             surface: &mut surface,
             ecb: &mut ecb,
+            desired_ecb: &mut desired_ecb,
             ledge_info: &mut ledge_info,
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
@@ -459,6 +490,7 @@ use crate::stage::line::StagePolyType;
                 origin: FGVec2::ZERO,
                 end: FGVec2::ZERO,
             },
+            waveland_snap_distance: FGi32::ZERO,
         };
 
         assert!(matches!(
@@ -498,15 +530,10 @@ pub fn grounded_movement_standstill_common_interrupts(
 pub fn perform_wavedash(input: &FighterInput, game_settings: &GameSettings) -> FighterState {
     // If aiming sideways and in the deadzone, do a perfect wavedash
     // TODO: Improve this so we don't have to go through the airborne state first
-    let mut wavedash_dir =
+    let mut wavedash_dir = input.get_last_frame().movement.normalize_or_zero();
-        input
-        .get_last_frame()
-        .movement
-        .normalize_or_zero();
     let movement = input.get_last_frame().movement;
     if movement.y.is_zero() && !movement.x.is_zero() {
-        wavedash_dir.y =
+        wavedash_dir.y = -game_settings.input_common.stick_deadzone - FGi32::lit("-0.01");
-            -game_settings.input_common.stick_deadzone - FGi32::lit("-0.01");
         wavedash_dir.x = movement.x.signum();
     }
 
@@ -517,4 +544,4 @@ pub fn perform_wavedash(input: &FighterInput, game_settings: &GameSettings) -> F
     FighterState::AirDodge(AirDodgeState {
         direction: wavedash_dir.normalize_or_zero(),
     })
-}
+}

src/fighter/state/hitstun.rs

@@ -1,8 +1,6 @@
 use crate::{
     fighter::{
-        animation::AnimKind,
+        animation::AnimKind, attack::{self, FighterHitReaction}, state::{
-        attack::{self, FighterHitReaction},
-        state::{
             CollisionContext, EnterContext, ExitContext, FighterState, FighterStateImpl,
             InterruptContext, UpdateContext,
             air::{self, AirborneStateCommon},
@@ -11,7 +9,7 @@ use crate::{
             land::LandingType,
             wait::WaitState,
         },
-    }, math::{int::FGi32, vec::FGVec2},
+    }, math::vec::FGVec2,
 };
 
 #[derive(Clone, Debug, Hash)]
@@ -25,14 +23,20 @@ pub struct HitstunState {
     pub hit_reaction: FighterHitReaction,
     pub hitstop_kind: HitstopStateKind,
     knockback_applied: bool,
+    stack_previous_knockback: bool,
 }
 
 impl HitstunState {
-    pub fn new(hit_reaction: FighterHitReaction, hitstop_kind: HitstopStateKind) -> Self {
+    pub fn new(
+        hit_reaction: FighterHitReaction,
+        hitstop_kind: HitstopStateKind,
+        stack_previous_knockback: bool,
+    ) -> Self {
         Self {
             hit_reaction,
             hitstop_kind,
             knockback_applied: false,
+            stack_previous_knockback,
         }
     }
 }
@@ -40,6 +44,35 @@ impl HitstunState {
 impl FighterStateImpl for HitstunState {
     const NAME: &'static str = "Hitstun";
 
+    fn check_interrupt(&self, state_context: &mut InterruptContext) -> Option<FighterState> {
+        if state_context.get_current_animation_frame() > self.hit_reaction.hitstun_frames {
+            match &self.hitstop_kind {
+                HitstopStateKind::Grounded => Some(FighterState::Wait(WaitState)),
+                HitstopStateKind::Airborne => Some(FighterState::Fall(FallState::new(
+                    AirborneStateCommon::default(),
+                ))),
+            }
+        } else {
+            None
+        }
+    }
+
+    fn on_enter(&mut self, state_context: &mut EnterContext) {
+        let animation = match self.hitstop_kind {
+            HitstopStateKind::Grounded => AnimKind::FlinchGround,
+            HitstopStateKind::Airborne => AnimKind::FlinchAir,
+        };
+        state_context.play_animation(animation, false);
+        state_context.velocity.0 = FGVec2::ZERO;
+    }
+
+    fn on_exit(&mut self, state_context: &mut ExitContext) {
+        if matches!(self.hitstop_kind, HitstopStateKind::Grounded) {
+            state_context.knockback_velocity.0 = FGVec2::ZERO;
+            state_context.knockback_state.clear();
+        }
+    }
+
     fn name(&self) -> String {
         let hitstop_kind = match self.hitstop_kind {
             HitstopStateKind::Grounded => "Grounded",
@@ -54,28 +87,29 @@ impl FighterStateImpl for HitstunState {
         format!("Hitstun ({hitstop_kind}, {hit_reaction_type})")
     }
 
-    fn check_interrupt(&self, state_context: &mut InterruptContext) -> Option<FighterState> {
-        if state_context.get_current_animation_frame() > self.hit_reaction.hitstun_frames {
-            match &self.hitstop_kind {
-                HitstopStateKind::Grounded => Some(FighterState::Wait(WaitState)),
-                HitstopStateKind::Airborne => Some(FighterState::Fall(FallState::new(
-                    AirborneStateCommon::default(),
-                ))),
-            }
-        } else {
-            None
-        }
-    }
-
     fn update(&mut self, ctx: &mut UpdateContext) {
         if !self.knockback_applied {
-            let launch_direction = attack::directional_influence::apply_directional_influence(
+            let new_launch_direction = attack::directional_influence::apply_directional_influence(
-                ctx.input.get_last_frame().movement,
+                FGVec2::ZERO,
                 self.hit_reaction.launch_angle,
                 ctx.game_settings.fighter_common.di_max_angle,
             );
+            let new_knockback = new_launch_direction * self.hit_reaction.launch_velocity;
+            let combined_knockback = if self.stack_previous_knockback {
+                attack::stack_knockback(ctx.knockback_velocity.0, new_knockback)
+            } else {
+                new_knockback
+            };
+            let launch_speed = combined_knockback.length();
+            let launch_direction =
+                attack::directional_influence::apply_directional_influence_to_direction(
+                    ctx.input.get_last_frame().movement,
+                    combined_knockback.normalize_or_zero(),
+                    ctx.game_settings.fighter_common.di_max_angle,
+                );
 
-            ctx.knockback_velocity.0 = launch_direction * self.hit_reaction.launch_velocity;
+            ctx.knockback_velocity.0 = launch_direction * launch_speed;
+            ctx.knockback_state.restart();
             self.knockback_applied = true;
         }
 
@@ -83,30 +117,19 @@ impl FighterStateImpl for HitstunState {
             HitstopStateKind::Grounded => {}
             HitstopStateKind::Airborne => {
                 air::integrate_gravity(ctx.velocity, ctx.fighter_attributes, false);
+                air::apply_air_motion_with_knockback(ctx);
             }
         }
 
-        let speed = ctx.knockback_velocity.length();
+        if matches!(self.hitstop_kind, HitstopStateKind::Grounded) {
-        let next_speed = speed
+            attack::decay_knockback(
-            .saturating_sub(ctx.game_settings.fighter_common.knockback_decay_per_frame)
+                ctx.knockback_velocity,
-            .max(FGi32::ZERO);
+                ctx.knockback_state,
-
+                ctx.game_settings.fighter_common.knockback_decay_per_frame,
-        ctx.knockback_velocity.0 = ctx.knockback_velocity.normalize_or_zero() * next_speed;
+            );
-
+        }
-        ctx.translation.0 += ctx.velocity.0 + ctx.knockback_velocity.0;
     }
 
-    fn on_enter(&mut self, state_context: &mut EnterContext) {
-        let animation = match self.hitstop_kind {
-            HitstopStateKind::Grounded => AnimKind::FlinchGround,
-            HitstopStateKind::Airborne => AnimKind::FlinchAir,
-        };
-        state_context.play_animation(animation, false);
-        state_context.velocity.0 = FGVec2::ZERO;
-    }
-
-    fn on_exit(&mut self, _state_context: &mut ExitContext) {}
-
     fn check_collision_interrupt(
         &mut self,
         state_context: &mut CollisionContext,
@@ -114,7 +137,7 @@ impl FighterStateImpl for HitstunState {
         match &mut self.hitstop_kind {
             HitstopStateKind::Grounded => collision_interrupt(state_context, true),
             HitstopStateKind::Airborne => {
-                air::collision_interrupt(state_context, LandingType::Normal, false)
+                air::collision_interrupt(state_context, LandingType::Normal, Default::default())
             }
         }
     }

src/fighter/state/jump.rs

@@ -99,6 +99,8 @@ impl FighterStateImpl for JumpSquatState {
 
     fn on_exit(&mut self, state_context: &mut crate::fighter::state::ExitContext) {
         state_context.input.disable_hold_all();
+        // We clear tap jump here, it may have weird interactions with air dodging up
+        state_context.input.clear_command(FighterCommands::TapJump);
     }
 
     fn is_visually_grounded<'a>(&'a self) -> bool {
@@ -174,7 +176,10 @@ impl FighterStateImpl for JumpState {
         air::collision_interrupt(
             state_context,
             crate::fighter::state::land::LandingType::Normal,
-            true,
+            crate::fighter::collision::AirCollisionOptions {
+                can_pass_through_soft_platforms: true,
+                ..Default::default()
+            },
         )
     }
 

src/fighter/state/ledge_action.rs

@@ -84,6 +84,7 @@ impl FighterStateImpl for LedgeActionState {
 
         state_context.velocity.0 = FGVec2::ZERO;
         state_context.knockback_velocity.0 = FGVec2::ZERO;
+        state_context.knockback_state.clear();
         let Some(ledge) = state_context.stage_collision.find_ledge_by_vertex(self.ledge_id) else {
             return;
         };
@@ -144,8 +145,9 @@ impl FighterStateImpl for LedgeActionState {
 
     fn check_collision_interrupt(
         &mut self,
-        _state_context: &mut CollisionContext,
+        state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
+        state_context.apply_desired_ecb();
         None
     }
 

src/fighter/state/ledge_grab.rs

@@ -36,6 +36,8 @@ impl FighterStateImpl for LedgeGrabState {
 
     fn on_enter(&mut self, state_context: &mut EnterContext) {
         state_context.play_animation(AnimKind::LedgeGrab, false);
+        state_context.knockback_velocity.0 = crate::math::vec::FGVec2::ZERO;
+        state_context.knockback_state.clear();
 
         *state_context.vulnerability = FighterInvulnerabilityState::Intangible {
             frames_remaining: None,

src/fighter/state/ledge_wait.rs

@@ -65,8 +65,9 @@ impl FighterStateImpl for LedgeWaitState {
     fn on_enter(&mut self, state_context: &mut EnterContext) {
         state_context.velocity.0 = FGVec2::ZERO;
         state_context.knockback_velocity.0 = FGVec2::ZERO;
+        state_context.knockback_state.clear();
         
-        if state_context.ledge_info.grab_count < state_context.game_settings.fighter_common.max_ledge_regrab_count {
+        if state_context.ledge_info.grab_count < state_context.game_settings.fighter_common.max_ledge_grab_count {
             *state_context.vulnerability = FighterInvulnerabilityState::Intangible {
                 frames_remaining: Some(
                     state_context
@@ -102,8 +103,9 @@ impl FighterStateImpl for LedgeWaitState {
 
     fn check_collision_interrupt(
         &mut self,
-        _state_context: &mut CollisionContext,
+        state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
+        state_context.apply_desired_ecb();
         None
     }
 

src/fighter/state/mod.rs

@@ -7,12 +7,12 @@ use bevy::prelude::*;
 
 use crate::fighter::animation::{AnimKind, FighterAnimationFrame};
 use crate::fighter::attack::{
-    FighterAttackScriptAssets, FighterKnockbackVelocity, FighterPendingHitReaction,
+    FighterAttackScriptAssets, FighterKnockbackState, FighterKnockbackVelocity,
-    FighterStaleMoveQueue, HitStop,
+    FighterPendingHitReaction, FighterStaleMoveQueue, HitStop,
 };
 use crate::fighter::attributes::FighterAttributes;
 use crate::fighter::baked_animation::{BakedFighterAnimations, FighterBoneMatrices};
-use crate::fighter::ecb::FighterPreviousECB;
+use crate::fighter::ecb::{self, FighterDesiredECB, FighterPreviousECB};
 use crate::fighter::manifest::FighterManifest;
 use crate::fighter::state::hitstun::HitstunState;
 use crate::fighter::surface::EcbLockPolicy;
@@ -49,14 +49,14 @@ pub mod ground_attack;
 pub mod hitstun;
 pub mod jump;
 pub mod land;
+pub mod ledge_action;
+pub mod ledge_grab;
+pub mod ledge_wait;
 pub mod platform_pass;
 pub mod run;
 pub mod turn;
 pub mod wait;
 pub mod walk;
-pub mod ledge_wait;
-pub mod ledge_action;
-pub mod ledge_grab;
 
 #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
 pub enum SurfacePolicy {
@@ -120,8 +120,9 @@ pub trait FighterStateImpl: Sized {
 
     fn check_collision_interrupt(
         &mut self,
-        _state_context: &mut CollisionContext,
+        state_context: &mut CollisionContext,
     ) -> Option<FighterState> {
+        state_context.apply_desired_ecb();
         None
     }
 
@@ -166,6 +167,7 @@ pub struct EnterContext<'a> {
     pub velocity: &'a mut FighterVelocity,
     pub translation: &'a mut FighterTranslation,
     pub knockback_velocity: &'a mut FighterKnockbackVelocity,
+    pub knockback_state: &'a mut FighterKnockbackState,
     pub stale_move_queue: &'a mut FighterStaleMoveQueue,
     pub facing_direction: &'a mut FighterFacingDirection,
     pub animation_frame: &'a mut FighterAnimationFrame,
@@ -192,10 +194,7 @@ impl EnterContext<'_> {
         let position = self
             .baked_animations
             .initial_root_position(self.animation_frame.kind, self.model_scale)?;
-        Some(
+        Some(self.translation.0 + animation_position_to_gameplay(position, self.facing_direction))
-            self.translation.0
-                + animation_position_to_gameplay(position, self.facing_direction),
-        )
     }
 
     pub fn get_animation_duration(&self, kind: AnimKind) -> Option<usize> {
@@ -206,6 +205,8 @@ impl EnterContext<'_> {
 pub struct ExitContext<'a> {
     pub input: &'a mut FighterInput,
     pub hitboxes: &'a mut FighterHitboxes,
+    pub knockback_velocity: &'a mut FighterKnockbackVelocity,
+    pub knockback_state: &'a mut FighterKnockbackState,
     pub surface: &'a mut FighterSurfaceState,
     pub vulnerability: &'a mut FighterInvulnerabilityState,
 }
@@ -218,6 +219,7 @@ pub struct UpdateContext<'a> {
     pub velocity: &'a mut FighterVelocity,
     pub surface: &'a mut FighterSurfaceState,
     pub knockback_velocity: &'a mut FighterKnockbackVelocity,
+    pub knockback_state: &'a mut FighterKnockbackState,
     pub vulnerability: &'a mut FighterInvulnerabilityState,
     pub ledge_info: &'a mut FighterLedgeInformation,
     pub game_settings: &'a GameSettings,
@@ -253,8 +255,11 @@ pub struct CollisionContext<'a> {
     pub prev_translation: &'a FighterPreviousTranslation,
     pub input: &'a FighterInput,
     pub velocity: &'a mut FighterVelocity,
+    pub knockback_velocity: &'a mut FighterKnockbackVelocity,
+    pub knockback_state: &'a mut FighterKnockbackState,
     pub surface: &'a mut FighterSurfaceState,
     pub ecb: &'a mut FighterECB,
+    pub desired_ecb: &'a mut FighterDesiredECB,
     pub prev_ecb: &'a FighterPreviousECB,
     pub stage_collision: &'a StageCollision,
     pub leave_ground_ecb_lock_duration: u32,
@@ -262,24 +267,32 @@ pub struct CollisionContext<'a> {
     pub ledge_info: &'a mut FighterLedgeInformation,
     pub fighter_ledge_collision_box: FGRect,
     pub downward_stick_threshold: FGi32,
+    pub waveland_snap_distance: FGi32,
 }
 
 impl CollisionContext<'_> {
+    /// Commit the target pose before resolving this frame. The collision
+    /// substep resolver can later replace this with fractional steps.
+    pub fn apply_desired_ecb(&mut self) {
+        ecb::interpolate_ecb(self.ecb, *self.desired_ecb, FGi32::ONE);
+    }
+
     pub fn air_collide_with_stage(
-        &self,
+        &mut self,
-        can_ignore_soft_platforms: bool,
+        mut options: crate::fighter::collision::AirCollisionOptions,
     ) -> Option<crate::fighter::collision::AirCollisionWithStageResult> {
         let ignored_polys = self.surface.ignored_polygon_ids();
-        let ignore_soft_platforms = can_ignore_soft_platforms
+        options.can_pass_through_soft_platforms = options.can_pass_through_soft_platforms
             && self.input.get_last_frame().movement.y <= -self.downward_stick_threshold;
-        crate::fighter::collision::air_collide_with_stage(
+        crate::fighter::collision::air_collide_with_stage_substepped(
             self.prev_translation,
             self.translation,
-            self.prev_ecb,
+            self.velocity,
             self.ecb,
+            self.desired_ecb,
             self.stage_collision,
             &ignored_polys,
-            ignore_soft_platforms,
+            options,
         )
     }
     pub fn air_collide_with_ledges(
@@ -328,8 +341,10 @@ pub struct FighterFrameQuery {
     pub velocity: &'static mut FighterVelocity,
     pub surface: &'static mut FighterSurfaceState,
     pub knockback_velocity: &'static mut FighterKnockbackVelocity,
+    pub knockback_state: &'static mut FighterKnockbackState,
     pub stale_move_queue: &'static mut FighterStaleMoveQueue,
     pub ecb: &'static mut FighterECB,
+    pub desired_ecb: &'static mut FighterDesiredECB,
     pub prev_ecb: &'static FighterPreviousECB,
     pub facing_direction: &'static mut FighterFacingDirection,
     pub animation_frame: &'static mut FighterAnimationFrame,
@@ -395,6 +410,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             hitboxes: &mut self.hitboxes,
             velocity: &mut self.velocity,
             knockback_velocity: &mut self.knockback_velocity,
+            knockback_state: &mut self.knockback_state,
             translation: &mut self.translation,
             stale_move_queue: &mut self.stale_move_queue,
             facing_direction: &mut self.facing_direction,
@@ -416,6 +432,8 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
         ExitContext {
             input: &mut self.input,
             hitboxes: &mut self.hitboxes,
+            knockback_velocity: &mut self.knockback_velocity,
+            knockback_state: &mut self.knockback_state,
             surface: &mut self.surface,
             vulnerability: &mut self.vulnerability,
         }
@@ -445,6 +463,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             velocity: &mut self.velocity,
             surface: &mut self.surface,
             knockback_velocity: &mut self.knockback_velocity,
+            knockback_state: &mut self.knockback_state,
             game_settings,
             animation_root_motion_delta,
             animation_root_position,
@@ -475,8 +494,11 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             presentation_snap: &mut self.presentation_snap,
             input: &self.input,
             velocity: &mut self.velocity,
+            knockback_velocity: &mut self.knockback_velocity,
+            knockback_state: &mut self.knockback_state,
             surface: &mut self.surface,
             ecb: &mut self.ecb,
+            desired_ecb: &mut self.desired_ecb,
             ledge_info: &mut self.ledge_information,
             prev_ecb: &self.prev_ecb,
             stage_collision,
@@ -485,6 +507,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
                 .leave_ground_ecb_frame_lock_duration,
             downward_stick_threshold: game_settings.input_common.run_stick_threshold,
             fighter_ledge_collision_box,
+            waveland_snap_distance: game_settings.fighter_common.waveland_snap_distance,
         }
     }
 }
@@ -645,9 +668,16 @@ pub fn state_interrupt_system(
             }
 
             info!("Entering hitstop kind: {:?}", hitstop_kind);
+            let stack_previous_knockback = !frame.surface.is_grounded()
+                && !frame.knockback_velocity.0.length_squared().is_zero()
+                && frame
+                    .knockback_state
+                    .can_stack(game_settings.fighter_common.knockback_stacking_window);
+
             Some(FighterState::Hitstun(HitstunState::new(
                 reaction,
                 hitstop_kind,
+                stack_previous_knockback,
             )))
         } else if hitstop.remaining_frames > 0 {
             None
@@ -743,6 +773,8 @@ pub fn state_collision_interrupt_system(
 
             // Clear hitstop
             hitstop.remaining_frames = 0;
+            frame.knockback_velocity.0 = FGVec2::ZERO;
+            frame.knockback_state.clear();
 
             // subtract one stock
 
@@ -757,6 +789,9 @@ pub fn state_collision_interrupt_system(
 
             // reset percentage
             *damage = FighterDamage::default();
+            // reset ledge
+
+            *frame.ledge_information = FighterLedgeInformation::default();
 
             transition_state(
                 &mut state,
@@ -833,9 +868,20 @@ mod tests {
         let input = FighterInput::default();
         let mut translation = FighterTranslation::default();
         let mut velocity = FighterVelocity::default();
+        let mut knockback_velocity = FighterKnockbackVelocity::default();
+        let mut knockback_state = FighterKnockbackState::default();
         let mut surface = FighterSurfaceState::default();
         let mut ecb = FighterECB::default();
-        let mut ledge_info = FighterLedgeInformation::default();
+        let mut desired_ecb = FighterDesiredECB {
+            top: FGVec2::lit("0", "2"),
+            bottom: FGVec2::ZERO,
+            left: FGVec2::lit("-1", "1"),
+            right: FGVec2::lit("1", "1"),
+        };
+        let mut ledge_info = FighterLedgeInformation {
+            regrab_lockout_remaining_frames: 5,
+            ..default()
+        };
         let previous_ecb = FighterPreviousECB::from(ecb);
         let mut presentation_snap = FighterPresentationSnap::default();
         let context = CollisionContext {
@@ -843,8 +889,11 @@ mod tests {
             prev_translation: &previous_translation,
             input: &input,
             velocity: &mut velocity,
+            knockback_velocity: &mut knockback_velocity,
+            knockback_state: &mut knockback_state,
             surface: &mut surface,
             ecb: &mut ecb,
+            desired_ecb: &mut desired_ecb,
             ledge_info: &mut ledge_info,
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
@@ -855,9 +904,11 @@ mod tests {
                 end: FGVec2::lit("1", "-1"),
             },
             downward_stick_threshold: FGi32::ONE,
+            waveland_snap_distance: FGi32::ZERO,
         };
 
         assert!(context.air_collide_with_ledges().is_none());
+        context.ledge_info.regrab_lockout_remaining_frames = 0;
         assert_eq!(
             context.air_collide_with_ledges().map(|result| result.ledge),
             Some(ledge_id)

src/fighter/state/platform_pass.rs

@@ -46,7 +46,10 @@ impl FighterStateImpl for PlatformPassState {
         air::collision_interrupt(
             state_context,
             crate::fighter::state::land::LandingType::Normal,
-            true,
+            crate::fighter::collision::AirCollisionOptions {
+                can_pass_through_soft_platforms: true,
+                ..Default::default()
+            },
         )
     }
     

src/game_settings.rs

@@ -18,6 +18,7 @@ pub struct FighterSettingsCommon {
 
     /// Ground friction applied when the fighter is above the walk speed
     pub ground_friction_over_walk_speed_multiplier: FGi32,
+    /// Minimum active launch frames between hits before airborne knockback stacks.
     pub knockback_stacking_window: u32,
     pub knockback_decay_per_frame: FGi32,
 
@@ -55,8 +56,8 @@ pub struct FighterSettingsCommon {
     pub ledge_drop_regrab_lockout_duration_frames: u32,
     /// How many frames (+ the ledge animation duration) the fighter will be invulnerable after grabbing the ledge
     pub ledge_grab_invulnerability_duration: u32,
-    /// How many times the fighter can regrab the ledge and still get invulnerability
+    /// How many times the fighter can grab the ledge without landing and still get invulnerability
-    pub max_ledge_regrab_count: u32,
+    pub max_ledge_grab_count: u32,
 
     /// When hit while the receiver is in the air, use this angle
     pub sakurai_angle_aerial_angle: FGi32,
@@ -66,6 +67,8 @@ pub struct FighterSettingsCommon {
     pub sakurai_angle_high_knockback_angle: FGi32,
     /// past this threshold, the knockback is considered high, so it will use [sakurai_angle_high_knockback_angle]
     pub sakurai_angle_knockback_threshold: FGi32,
+
+    pub waveland_snap_distance: FGi32,
 }
 #[derive(Reflect, Serialize, Deserialize, Clone)]
 #[reflect(opaque)]

src/hitbox_viewer/mod.rs

@@ -10,6 +10,7 @@ use bevy::{
     world_serialization::WorldAssetRoot,
 };
 use bevy_egui::{EguiContexts, EguiPrimaryContextPass, egui};
+use bevy_ggrs::SnapshotPlugin;
 use clap::{Parser, ValueEnum};
 use egui_extras::Column;
 use itertools::Itertools;
@@ -131,6 +132,7 @@ impl Plugin for HitboxViewerPlugin {
             )
         };
         app.add_plugins((
+            SnapshotPlugin,
             GameAssetPlugin,
             FighterScriptImportPlugin,
             BakedAnimationAssetProcessingPlugin,

src/input/buffer.rs

@@ -717,7 +717,6 @@ pub fn postprocess_input(
                 FighterAttackCommandType::Neutral
             };
 
-            dbg!(input.movement_flick.y, attack_type);
             input.set_lifetime(FighterCommands::Attack, tap);
             input.set_attack_command_type(attack_type);
         }

src/stage/debug.rs

@@ -1,15 +1,15 @@
 use bevy::{color::palettes::css::RED, prelude::*};
 
 use crate::{
-    match_loading::MatchConfig, math::{int::FGi32, vec3::FGVec3}, stage::{
+    game_settings::GameSettings, match_loading::MatchConfig, math::{int::FGi32, vec3::FGVec3}, stage::{
-        line::{StageCollision, StageLedgeSide},
+        line::{StageCollision, StageLedgeSide, StagePolyLineSegmentType}, manifest::{StageManifest, StageManifestRegistry},
-        manifest::{StageManifest, StageManifestRegistry},
     },
 };
 
-pub fn debug_draw_scene(mut gizmos: Gizmos, stage_collision: Res<StageCollision>) {
+pub fn debug_draw_scene(mut gizmos: Gizmos, stage_collision: Res<StageCollision>, game_settings: Res<GameSettings>) {
     for poly in stage_collision.stage_polys.iter() {
-        for segment in &poly.segments {
+        for (segment, next_segment) in poly.segments.iter().zip(poly.segments.iter().cycle().skip(1)) {
+            let wavedash_normal = ((next_segment.normal.to_vec2() + segment.normal.to_vec2()) * 0.5).normalize();
             let from = segment.segment.point1().to_vec2();
             let to = segment.segment.point2().to_vec2();
             let from_3d = Vec3::new(from.x, from.y, 0.0);
@@ -18,6 +18,16 @@ pub fn debug_draw_scene(mut gizmos: Gizmos, stage_collision: Res<StageCollision>
             gizmos.line(from_3d, end_3d, RED);
             let midpoint = (from_3d + end_3d) * 0.5;
             gizmos.arrow(midpoint, midpoint + normal_3d, RED);
+            if matches!(segment.segment_type, StagePolyLineSegmentType::Floor) {
+                let radius = game_settings.fighter_common.waveland_snap_distance.to_num::<f32>();
+                let a = segment.segment.point1().to_vec2();
+                let a = Vec3::new(a.x, a.y, 0.0);
+                let b = segment.segment.point2().to_vec2();
+                let b = Vec3::new(b.x, b.y, 0.0);
+                let offset = Vec3::new(wavedash_normal.x, wavedash_normal.y, 0.0) * radius;
+                gizmos.line(a + offset, b + offset, bevy::color::palettes::css::HOT_PINK);
+                gizmos.line(a - offset, b - offset, bevy::color::palettes::css::HOT_PINK);
+            }
         }
     }