Improve ECB behaviour, add ECB interpolation, wall/ceiling support etc

src/debug_tools/save_state.rs

@@ -1,12 +1,25 @@
 use bevy::prelude::*;
 
 use crate::{
-    camera::MatchCamera, fighter::{
-        FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop, FighterHitstopShake, FighterInvulnerabilityState, FighterLedgeInformation, FighterPendingRespawn, FighterPreviousFacingDirection, FighterPreviousTranslation, FighterSurfaceState, FighterTranslation, FighterVelocity, animation::FighterAnimationFrame, attack::{
+    camera::MatchCamera,
+    fighter::{
+        FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop, FighterHitstopShake,
+        FighterInvulnerabilityState, FighterLedgeInformation, FighterPendingRespawn,
+        FighterPreviousFacingDirection, FighterPreviousTranslation, FighterSurfaceState,
+        FighterTranslation, FighterVelocity,
+        animation::FighterAnimationFrame,
+        attack::{
             FighterDamage, FighterKnockbackVelocity, FighterPendingHitReaction, FighterPendingHits,
             FighterSolvedHurtboxes, FighterStaleMoveQueue,
-        }, baked_animation::FighterBoneMatrices, state::FighterState,
-    }, input::FighterInput, match_runtime::MatchState, player::Player, stage::line::StageCollision,
+        },
+        baked_animation::FighterBoneMatrices,
+        ecb::FighterDesiredECB,
+        state::FighterState,
+    },
+    input::FighterInput,
+    match_runtime::MatchState,
+    player::Player,
+    stage::line::StageCollision,
 };
 
 #[derive(Resource, Default)]
@@ -27,6 +40,7 @@ struct FighterCheckpoint {
     entity: Entity,
     handle: usize,
     ecb: FighterECB,
+    desired_ecb: FighterDesiredECB,
     previous_ecb: crate::fighter::ecb::FighterPreviousECB,
     velocity: FighterVelocity,
     translation: FighterTranslation,
@@ -131,6 +145,7 @@ 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);
@@ -169,6 +184,7 @@ 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>()?,

src/fighter/collision.rs

@@ -1,11 +1,17 @@
 //! Resolving an integrated fighter position against the stage.
 
-use crate::fighter::ecb::FighterPreviousECB;
-use crate::fighter::{FighterECB, FighterPreviousTranslation, FighterTranslation};
+use crate::fighter::ecb::{self as ecb_module, FighterDesiredECB};
+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)>,
@@ -36,10 +42,14 @@ 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(
+#[cfg(test)]
+fn air_collide_with_stage(
     prev_translation: &FighterPreviousTranslation,
     translation: &FighterTranslation,
     prev_ecb: &FighterPreviousECB,
@@ -48,42 +58,298 @@ pub fn air_collide_with_stage(
     ignored_polys: &[usize],
     can_ignore_soft_platforms: bool,
 ) -> Option<AirCollisionWithStageResult> {
-    let ray_segment = FGSegment2d::new(
-        prev_translation.0 + prev_ecb.get_bottom_point(),
-        translation.0 + ecb.get_bottom_point(),
-    );
+    let mut translation = *translation;
+    let mut velocity = FighterVelocity::default();
+    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,
+        can_ignore_soft_platforms,
+    )
+}
 
+/// 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],
+    can_ignore_soft_platforms: bool,
+) -> 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,
+            can_ignore_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);
+        }
+
+        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_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)
-                && !(can_ignore_soft_platforms && matches!(poly.poly_type, StagePolyType::Platform))
+                && !(ignore_platforms && matches!(poly.poly_type, StagePolyType::Platform))
         })
-        .filter_map(|(poly_idx, poly)| {
-            poly.intersect_ray(ray_segment).map(|intersect_result| {
-                (
-                    AirCollisionWithStageResult {
-                        line_id: {
-                            StageLineID {
-                                polygon: poly_idx,
-                                segment: intersect_result.segment_idx,
+        .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;
                             }
-                        },
-                        hit_position: intersect_result.position,
-                        hit_normal: intersect_result.normal,
-                    },
-                    intersect_result
-                        .position
-                        .distance_squared(ray_segment.point2()),
-                )
-            })
+
+                            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 +359,11 @@ pub fn air_collide_with_ledges(
     ledge_box: &FGRect,
     stage_collision: &StageCollision,
 ) -> Option<AirCollisionWithLedgeResult> {
-    stage_collision.intersect_ledges(ledge_box).map(|result| {
-        AirCollisionWithLedgeResult { ledge: result.vertex_id }
-    })
+    stage_collision
+        .intersect_ledges(ledge_box)
+        .map(|result| AirCollisionWithLedgeResult {
+            ledge: result.vertex_id,
+        })
 }
 
 #[cfg(test)]
@@ -126,6 +394,173 @@ 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,
+            &[],
+            false,
+        )
+        .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,
+            &[],
+            false,
+        )
+        .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,
+            &[],
+            false,
+        )
+        .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,
+            &[],
+            false,
+        )
+        .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 {
@@ -183,16 +618,18 @@ mod tests {
             right: FGVec2::ZERO,
         };
 
-        assert!(air_collide_with_stage(
-            &previous_translation,
-            &translation,
-            &previous_ecb,
-            &ecb,
-            &stage_collision,
-            &[],
-            true,
-        )
-        .is_none());
+        assert!(
+            air_collide_with_stage(
+                &previous_translation,
+                &translation,
+                &previous_ecb,
+                &ecb,
+                &stage_collision,
+                &[],
+                true,
+            )
+            .is_none()
+        );
 
         assert_eq!(
             air_collide_with_stage(

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 Some((_, bone_matrix)) = bone_matrices.get_by_idx(*idx) else {
-                return None;
-            };
+        let transformed_ecb_bones = bone_indices
+            .indices
+            .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)
-        }).collect::<Vec<_>>();
+                Some(FGVec2::new(pt.x, pt.y) - translation.0)
+            })
+            .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 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 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 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;
-        ecb.right = right;
+        desired.left = left;
+        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,
             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> },
-    Intangible { frames_remaining: Option<u32> }
+    Invulnerable {
+        frames_remaining: Option<u32>,
+    },
+    Intangible {
+        frames_remaining: Option<u32>,
+    },
 }
 
 impl FighterFacingDirection {
@@ -197,7 +214,7 @@ pub struct FighterPendingRespawn(bool);
     FighterKnockbackVelocity,
     FighterTranslation,
     FighterInvulnerabilityState,
-    FighterInvulnerabilityVisualState,
+    FighterInvulnerabilityVisualState
 )]
 pub struct Fighter {
     pub manifest: Handle<FighterManifest>,
@@ -226,7 +243,11 @@ impl Plugin for FighterPlugin {
             )
             .add_systems(
                 GgrsSchedule,
-                (state::state_update_system, decay_hitstop, decay_invulnerability)
+                (
+                    state::state_update_system,
+                    decay_hitstop,
+                    decay_invulnerability,
+                )
                     .chain()
                     .in_set(GameplaySet::StateUpdate),
             )
@@ -241,11 +262,12 @@ impl Plugin for FighterPlugin {
                 (
                     (
                         blast_zones::apply_blast_zones,
-                        ecb::update_ecb,
                         ecb::decrement_ecb_lockout,
+                        ecb::update_ecb,
                         state::state_collision_interrupt_system,
                         decay_ledge_grab_lockout,
-                    ).chain(),
+                    )
+                        .chain(),
                     baked_animation::resample_fighter_bone_matrices,
                 )
                     .chain()
@@ -272,6 +294,8 @@ 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>()
@@ -335,8 +359,9 @@ impl Plugin for FighterPlugin {
                     .run_if(crate::debug_tools::attack_hitboxes_enabled)
                     .run_if(in_state(AppState::InMatch)),
             )
-            .add_systems(FixedPostUpdate, 
-                visual::update_status_colors.run_if(resource_exists::<GameSettings>)
+            .add_systems(
+                FixedPostUpdate,
+                visual::update_status_colors.run_if(resource_exists::<GameSettings>),
             )
             .add_systems(
                 FixedPostUpdate,
@@ -396,10 +421,11 @@ 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 +475,7 @@ 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 +483,7 @@ pub fn decay_invulnerability(query: Query<&mut FighterInvulnerabilityState>) {
                 } else {
                     None
                 }
-            },
+            }
         };
 
         if let Some(frames_remaining) = frames_remaining {

src/fighter/state/air.rs

@@ -134,12 +134,10 @@ pub fn collision_interrupt(
     }
 
     let res = ctx.air_collide_with_stage(can_ignore_soft_platforms)?;
-    let diff = res.hit_position - ctx.translation.0;
-    ctx.ecb.bottom -= diff;
-    ctx.ecb.top -= diff;
-    ctx.ecb.left -= diff;
-    ctx.ecb.right -= diff;
-    ctx.translation.0 = res.hit_position;
+    ctx.translation.0 = res.resolved_translation;
+    let bottom_offset = ctx.ecb.rebase_onto_bottom();
+    ctx.translation.0 += bottom_offset;
+    *ctx.desired_ecb = crate::fighter::ecb::FighterDesiredECB::from(*ctx.ecb);
     ctx.presentation_snap.0 = true;
     ctx.surface.land(res.line_id, ctx.ledge_info);
     Some(FighterState::Land(LandingState::create(landing_type)))

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,
-};
-use crate::fighter::{
-    FighterAttributes, FighterTranslation, FighterVelocity,
+    CollisionContext, FighterState, InterruptContext, air, crouch, dash, fall, ground_attack, turn,
+    wait, walk,
 };
+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(
-    velocity: &FighterVelocity,
-    translation: &mut FighterTranslation,
-) {
+pub fn apply_grounded_motion(velocity: &FighterVelocity, translation: &mut FighterTranslation) {
     // Vertical velocity should be 0 on the ground
     translation.0 += FGVec2::new(velocity.0.x, FGi32::ZERO);
 }
@@ -176,61 +175,80 @@ pub fn collide_with_stage_grounded(
     state_context: &mut CollisionContext,
     can_walk_off: bool,
 ) -> GroundedMotionResult {
-    let translation = &mut state_context.translation;
-    let ecb = &state_context.ecb;
-    let stage_collision = state_context.stage_collision;
-
-    let Some(current_line_id) = state_context.surface.line_id() else {
+    let Some(mut line_id) = state_context.surface.line_id() else {
+        state_context.apply_desired_ecb();
         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 ecb_bottom_pos = translation.0 + ecb.get_bottom_point();
+        let Some(stage_poly) = state_context.stage_collision.stage_polys.get(line_id.polygon) else {
+            *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,
+            );
+            state_context.ecb_advanced = true;
+            return GroundedMotionResult::InAir;
+        };
         match resolve_grounded_position(
             stage_poly,
-            current_line_id.segment,
-            ecb_bottom_pos,
+            line_id.segment,
+            current_position + current_ecb.bottom,
             can_walk_off,
         ) {
-            GroundedPositionResult::InGround {
-                point,
-                segment_idx,
-                blocked,
-            } => {
-                let current_segment = stage_poly.get_segment(segment_idx).unwrap();
-                translation.0 = point - ecb.get_bottom_point();
+            GroundedPositionResult::InGround { point, segment_idx, blocked } => {
+                line_id.segment = segment_idx;
+                current_position = point - current_ecb.bottom;
+                let segment = stage_poly.get_segment(segment_idx).unwrap();
                 state_context.velocity.0 = if blocked {
                     FGVec2::ZERO
                 } else {
                     state_context.velocity.0
-                        - state_context
-                            .velocity
-                            .0
-                            .project_onto_normalized(current_segment.normal)
+                        - state_context.velocity.0.project_onto_normalized(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
+                state_context.ecb_advanced = true;
+                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);
+    state_context.ecb_advanced = true;
+    GroundedMotionResult::InGround
 }
 
 pub fn collision_interrupt(ctx: &mut CollisionContext, can_walk_off: bool) -> Option<FighterState> {
@@ -245,11 +263,13 @@ 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::{FighterECB, FighterLedgeInformation, FighterPreviousTranslation, FighterSurfaceState};
-    use crate::math::rect::FGRect;
-use crate::stage::line::StagePolyType;
+    use crate::fighter::ecb::{FighterDesiredECB, FighterPreviousECB};
+    use crate::fighter::{
+        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(
@@ -379,6 +399,7 @@ 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 context = CollisionContext {
             translation: &mut translation,
@@ -387,6 +408,7 @@ use crate::stage::line::StagePolyType;
             velocity: &mut velocity,
             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 +419,7 @@ use crate::stage::line::StagePolyType;
                 origin: FGVec2::ZERO,
                 end: FGVec2::ZERO,
             },
+            ecb_advanced: false,
         };
 
         assert!(matches!(
@@ -440,6 +463,7 @@ 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 {
@@ -449,6 +473,7 @@ use crate::stage::line::StagePolyType;
             velocity: &mut velocity,
             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 +484,7 @@ use crate::stage::line::StagePolyType;
                 origin: FGVec2::ZERO,
                 end: FGVec2::ZERO,
             },
+            ecb_advanced: false,
         };
 
         assert!(matches!(
@@ -498,15 +524,10 @@ 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 =
-        input
-        .get_last_frame()
-        .movement
-        .normalize_or_zero();
+    let mut wavedash_dir = 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 =
-            -game_settings.input_common.stick_deadzone - FGi32::lit("-0.01");
+        wavedash_dir.y = -game_settings.input_common.stick_deadzone - FGi32::lit("-0.01");
         wavedash_dir.x = movement.x.signum();
     }
 

src/fighter/state/mod.rs

@@ -12,7 +12,7 @@ use crate::fighter::attack::{
 };
 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 {
@@ -192,10 +192,7 @@ impl EnterContext<'_> {
         let position = self
             .baked_animations
             .initial_root_position(self.animation_frame.kind, self.model_scale)?;
-        Some(
-            self.translation.0
-                + animation_position_to_gameplay(position, self.facing_direction),
-        )
+        Some(self.translation.0 + animation_position_to_gameplay(position, self.facing_direction))
     }
 
     pub fn get_animation_duration(&self, kind: AnimKind) -> Option<usize> {
@@ -255,6 +252,7 @@ pub struct CollisionContext<'a> {
     pub velocity: &'a mut FighterVelocity,
     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,
@@ -262,25 +260,42 @@ pub struct CollisionContext<'a> {
     pub ledge_info: &'a mut FighterLedgeInformation,
     pub fighter_ledge_collision_box: FGRect,
     pub downward_stick_threshold: FGi32,
+    pub(crate) ecb_advanced: bool,
 }
 
 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);
+        self.ecb_advanced = true;
+    }
+
     pub fn air_collide_with_stage(
-        &self,
+        &mut self,
         can_ignore_soft_platforms: bool,
     ) -> Option<crate::fighter::collision::AirCollisionWithStageResult> {
         let ignored_polys = self.surface.ignored_polygon_ids();
         let ignore_soft_platforms = can_ignore_soft_platforms
             && self.input.get_last_frame().movement.y <= -self.downward_stick_threshold;
-        crate::fighter::collision::air_collide_with_stage(
+        let result = 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,
-        )
+        );
+        self.ecb_advanced = true;
+        result
+    }
+
+    fn finish_ecb_frame(&mut self) {
+        if !self.ecb_advanced {
+            self.apply_desired_ecb();
+        }
     }
     pub fn air_collide_with_ledges(
         &self,
@@ -330,6 +345,7 @@ pub struct FighterFrameQuery {
     pub knockback_velocity: &'static mut FighterKnockbackVelocity,
     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,
@@ -477,6 +493,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             velocity: &mut self.velocity,
             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 +502,7 @@ 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,
+            ecb_advanced: false,
         }
     }
 }
@@ -500,7 +518,6 @@ pub struct StatefulFighterQuery {
     pub player: &'static Player,
     pub pending_hit_reaction: &'static mut FighterPendingHitReaction,
     pub hitstop: &'static mut FighterHitstop,
-    pub ledge_info: &'static mut FighterLedgeInformation,
     pub hitstop_shake: &'static mut FighterHitstopShake,
     pub pending_respawn: &'static mut FighterPendingRespawn,
     pub damage: &'static mut FighterDamage,
@@ -710,7 +727,6 @@ pub fn state_collision_interrupt_system(
             mut pending_respawn,
             player,
             mut damage,
-            mut ledge_info,
             ..
         } = fighter;
 
@@ -761,7 +777,7 @@ pub fn state_collision_interrupt_system(
             *damage = FighterDamage::default();
             // reset ledge
 
-            *ledge_info = FighterLedgeInformation::default();
+            *frame.ledge_information = FighterLedgeInformation::default();
 
             transition_state(
                 &mut state,
@@ -781,9 +797,13 @@ pub fn state_collision_interrupt_system(
             continue;
         }
 
-        let new_state = state.check_collision_interrupt(
-            &mut frame.collision_context(&stage_collision, manifest, &game_settings),
-        );
+        let new_state = {
+            let mut collision_context =
+                frame.collision_context(&stage_collision, manifest, &game_settings);
+            let new_state = state.check_collision_interrupt(&mut collision_context);
+            collision_context.finish_ecb_frame();
+            new_state
+        };
         if let Some(new_state) = new_state {
             transition_state(
                 &mut state,
@@ -840,19 +860,26 @@ mod tests {
         let mut velocity = FighterVelocity::default();
         let mut surface = FighterSurfaceState::default();
         let mut ecb = FighterECB::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 {
+        let mut context = CollisionContext {
             translation: &mut translation,
             prev_translation: &previous_translation,
             input: &input,
             velocity: &mut velocity,
             surface: &mut surface,
             ecb: &mut ecb,
+            desired_ecb: &mut desired_ecb,
             ledge_info: &mut ledge_info,
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
@@ -863,6 +890,7 @@ mod tests {
                 end: FGVec2::lit("1", "-1"),
             },
             downward_stick_threshold: FGi32::ONE,
+            ecb_advanced: false,
         };
 
         assert!(context.air_collide_with_ledges().is_none());
@@ -871,5 +899,7 @@ mod tests {
             context.air_collide_with_ledges().map(|result| result.ledge),
             Some(ledge_id)
         );
+        context.finish_ecb_frame();
+        assert_eq!(context.ecb.top, FGVec2::lit("0", "2"));
     }
 }