Implement land from below, fix attacks not lifting fighters off the ground (#96)

Reviewed-on: #96
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/collision.rs

@@ -48,6 +48,14 @@ pub struct AirCollisionWithStageResult {
     pub hit_normal: FGVec2,
 }
 
+#[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,
@@ -56,7 +64,7 @@ fn air_collide_with_stage(
     ecb: &FighterECB,
     stage_collision: &StageCollision,
     ignored_polys: &[usize],
-    can_ignore_soft_platforms: bool,
+    options: AirCollisionOptions,
 ) -> Option<AirCollisionWithStageResult> {
     let mut translation = *translation;
     let mut velocity = FighterVelocity::default();
@@ -73,7 +81,7 @@ fn air_collide_with_stage(
         &FighterDesiredECB::from(*ecb),
         stage_collision,
         ignored_polys,
-        can_ignore_soft_platforms,
+        options,
     )
 }
 
@@ -101,7 +109,7 @@ pub fn air_collide_with_stage_substepped(
     desired: &FighterDesiredECB,
     stage_collision: &StageCollision,
     ignored_polys: &[usize],
-    can_ignore_soft_platforms: bool,
+    options: AirCollisionOptions,
 ) -> Option<AirCollisionWithStageResult> {
     let requested_translation = translation.0;
     let movement = requested_translation - prev_translation.0;
@@ -151,7 +159,7 @@ pub fn air_collide_with_stage_substepped(
             &lower_edges,
             StagePolyLineSegmentType::Floor,
             ignored_polys,
-            can_ignore_soft_platforms,
+            options.can_pass_through_soft_platforms,
         ) {
             *ecb = current_ecb;
             translation.0 = current_position + result.correction;
@@ -193,6 +201,26 @@ pub fn air_collide_with_stage_substepped(
             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,
@@ -245,6 +273,59 @@ struct PointSweepResult {
     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) && matches!(poly.poly_type, StagePolyType::Platform)
+        })
+        .flat_map(|(poly_idx, poly)| {
+            poly.segments
+                .iter()
+                .enumerate()
+                .filter(|(_, segment)| {
+                    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: segment_idx,
+                            },
+                            hit_normal: segment.normal,
+                            correction: hit_position - current_bottom,
+                        },
+                        hit_position.distance_squared(previous_bottom),
+                    ))
+                })
+        })
+        .min_by_key(|(_, distance)| *distance)
+        .map(|(result, _)| result)
+}
+
 fn sweep_edges(
     stage_collision: &StageCollision,
     previous_position: FGVec2,
@@ -442,7 +523,7 @@ mod tests {
             &desired,
             &stage_collision,
             &[],
-            false,
+            Default::default(),
         )
         .expect("the floor should be hit");
 
@@ -482,7 +563,7 @@ mod tests {
             &desired,
             &stage_collision,
             &[],
-            false,
+            Default::default(),
         )
         .is_none());
         assert_eq!(translation.0, FGVec2::lit("3", "0"));
@@ -518,7 +599,7 @@ mod tests {
             &desired,
             &stage_collision,
             &[],
-            false,
+            Default::default(),
         )
         .is_none());
         assert_eq!(translation.0.x, FGi32::lit("3"));
@@ -554,7 +635,7 @@ mod tests {
             &desired,
             &stage_collision,
             &[],
-            false,
+            Default::default(),
         )
         .is_none());
         assert_eq!(translation.0, FGVec2::lit("0", "1"));
@@ -589,7 +670,7 @@ mod tests {
             &ecb,
             &stage_collision,
             &[1],
-            false,
+            Default::default(),
         )
         .expect("the non-ignored platform should still be collidable");
 
@@ -626,7 +707,10 @@ mod tests {
                 &ecb,
                 &stage_collision,
                 &[],
-                true,
+                AirCollisionOptions {
+                    can_pass_through_soft_platforms: true,
+                    ..Default::default()
+                },
             )
             .is_none()
         );
@@ -639,7 +723,7 @@ mod tests {
                 &ecb,
                 &stage_collision,
                 &[],
-                false,
+                Default::default(),
             )
             .expect("air dodges still collide with soft platforms")
             .hit_position,
@@ -675,11 +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/mod.rs

@@ -245,7 +245,6 @@ impl Plugin for FighterPlugin {
                 GgrsSchedule,
                 (
                     state::state_update_system,
-                    decay_hitstop,
                     decay_invulnerability,
                 )
                     .chain()
@@ -265,6 +264,8 @@ impl Plugin for FighterPlugin {
                         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(),

src/fighter/state/air.rs

@@ -125,7 +125,7 @@ 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() {
@@ -134,7 +134,7 @@ pub fn collision_interrupt(
         }
     }
 
-    let res = ctx.air_collide_with_stage(can_ignore_soft_platforms)?;
+    let res = ctx.air_collide_with_stage(options)?;
     ctx.translation.0 = res.resolved_translation;
     let bottom_offset = ctx.ecb.rebase_onto_bottom();
     ctx.translation.0 += bottom_offset;

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

@@ -65,7 +65,14 @@ impl FighterStateImpl for AirDodgeState {
             }
         }
 
-        air::collision_interrupt(state_context, LandingType::Special, false)
+        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/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/hitstun.rs

@@ -1,8 +1,6 @@
 use crate::{
     fighter::{
-        animation::AnimKind,
-        attack::{self, FighterHitReaction},
-        state::{
+        FighterVelocity, animation::AnimKind, attack::{self, FighterHitReaction}, state::{
             CollisionContext, EnterContext, ExitContext, FighterState, FighterStateImpl,
             InterruptContext, UpdateContext,
             air::{self, AirborneStateCommon},
@@ -40,6 +38,30 @@ 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) {}
+
     fn name(&self) -> String {
         let hitstop_kind = match self.hitstop_kind {
             HitstopStateKind::Grounded => "Grounded",
@@ -54,19 +76,6 @@ 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(
@@ -83,6 +92,8 @@ impl FighterStateImpl for HitstunState {
             HitstopStateKind::Grounded => {}
             HitstopStateKind::Airborne => {
                 air::integrate_gravity(ctx.velocity, ctx.fighter_attributes, false);
+                let vel_with_kb = FighterVelocity(ctx.velocity.0 + ctx.knockback_velocity.0);
+                air::apply_air_motion(&vel_with_kb, ctx.translation, ctx.prev_translation);
             }
         }
 
@@ -92,21 +103,8 @@ impl FighterStateImpl for HitstunState {
             .max(FGi32::ZERO);
 
         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 +112,7 @@ 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/mod.rs

@@ -273,10 +273,10 @@ impl CollisionContext<'_> {
 
     pub fn air_collide_with_stage(
         &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_substepped(
             self.prev_translation,
@@ -286,7 +286,7 @@ impl CollisionContext<'_> {
             self.desired_ecb,
             self.stage_collision,
             &ignored_polys,
-            ignore_soft_platforms,
+            options,
         )
     }
     pub fn air_collide_with_ledges(

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()
+            },
         )
     }