Fix fighter visuals after landing snap (#67)

## Summary

- Mark landing position corrections as presentation discontinuities.
- Render and frame fighters from the current position for the snap frame.
- Keep previous translation history unchanged for gameplay collision and attack logic.

Reviewed-on: #67
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/camera/mod.rs

@@ -5,7 +5,7 @@ use bevy_ggrs::GgrsFrameTiming;
 
 use crate::{
     debug_tools::DebugSettings,
-    fighter::{manifest::FighterManifest, motion::sample_presentation_translation},
+    fighter::{manifest::FighterManifest, motion::{sample_presentation_translation_with_snap, FighterPresentationSnap}},
     stage::manifest::StageCameraProfile,
 };
 
@@ -313,6 +313,7 @@ fn update_match_camera(
             &crate::fighter::motion::FighterPreviousTranslation,
             &crate::fighter::Fighter,
             &crate::fighter::FighterFacingDirection,
+            &FighterPresentationSnap,
             &mut FighterCameraExtents,
         ),
         With<crate::player::Player>,
@@ -329,16 +330,17 @@ fn update_match_camera(
     let subjects = fighters
         .iter_mut()
         .map(
-            |(translation, previous_translation, fighter, facing, mut extents)| {
+            |(translation, previous_translation, fighter, facing, presentation_snap, mut extents)| {
                 let manifest = manifests
                     .get(&fighter.manifest)
                     .expect("Fighter manifest should be valid");
                 fighter_subject_bounds(
-                    sample_presentation_translation(
+                    sample_presentation_translation_with_snap(
                         *previous_translation,
                         *translation,
                         timing.overstep_fraction(),
                         debug_settings.motion_sampling,
+                        *presentation_snap,
                     ),
                     manifest.camera,
                     *facing,
@@ -465,6 +467,7 @@ fn debug_draw_camera(
             &crate::fighter::motion::FighterPreviousTranslation,
             &crate::fighter::Fighter,
             &crate::fighter::FighterFacingDirection,
+            &FighterPresentationSnap,
             &FighterCameraExtents,
         ),
         With<crate::player::Player>,
@@ -486,15 +489,16 @@ fn debug_draw_camera(
             Color::srgb(1.0, 0.5, 0.0),
         );
         draw_rectangle(&mut gizmos, camera.frame, Color::srgb(1.0, 1.0, 0.0));
-        for (translation, previous_translation, fighter, _facing, extents) in &fighters {
+        for (translation, previous_translation, fighter, _facing, presentation_snap, extents) in &fighters {
             let manifest = manifests
                 .get(&fighter.manifest)
                 .expect("Fighter manifest should be valid");
-            let center = sample_presentation_translation(
+            let center = sample_presentation_translation_with_snap(
                 *previous_translation,
                 *translation,
                 timing.overstep_fraction(),
                 debug_settings.motion_sampling,
+                *presentation_snap,
             ) + Vec2::Y * manifest.camera.vertical_origin_offset.to_num::<f32>();
             draw_rectangle(
                 &mut gizmos,

src/fighter/mod.rs

@@ -29,7 +29,8 @@ pub use attributes::FighterAttributes;
 pub use ecb::FighterECB;
 pub use manifest::FighterId;
 pub use motion::{
-    FighterPreviousFacingDirection, FighterPreviousTranslation, FighterTranslation, FighterVelocity,
+    FighterPresentationSnap, FighterPreviousFacingDirection, FighterPreviousTranslation,
+    FighterTranslation, FighterVelocity,
 };
 pub use surface::FighterSurfaceState;
 
@@ -147,6 +148,10 @@ impl Plugin for FighterPlugin {
     fn build(&self, app: &mut App) {
         app.add_plugins(FighterAttackPlugin)
             // Every state gets a chance to interrupt itself, in priority order.
+            .add_systems(
+                GgrsSchedule,
+                motion::clear_fighter_presentation_snaps.in_set(GameplaySet::Input),
+            )
             .add_systems(
                 GgrsSchedule,
                 (
@@ -202,6 +207,8 @@ impl Plugin for FighterPlugin {
             .checksum_component_with_hash::<FighterTranslation>()
             .rollback_component_with_copy::<FighterPreviousTranslation>()
             .checksum_component_with_hash::<FighterPreviousTranslation>()
+            .rollback_component_with_copy::<FighterPresentationSnap>()
+            .checksum_component_with_hash::<FighterPresentationSnap>()
             .rollback_component_with_copy::<FighterPreviousFacingDirection>()
             .checksum_component_with_hash::<FighterPreviousFacingDirection>()
             .rollback_component_with_copy::<animation::FighterAnimationFrame>()
@@ -304,6 +311,7 @@ pub fn spawn_fighter(
                 FighterVelocity::default(),
                 FighterTranslation(spawn_position),
                 FighterPreviousTranslation(spawn_position),
+                FighterPresentationSnap::default(),
             ),
             visual_root,
             animations,

src/fighter/motion.rs

@@ -21,6 +21,11 @@ pub struct FighterVelocity(pub FGVec2);
 #[derive(Component, Deref, DerefMut, Default, Clone, Copy, Hash)]
 pub struct FighterPreviousTranslation(pub FGVec2);
 
+/// Marks a simulation frame whose position changed discontinuously for
+/// presentation purposes (for example, a landing correction).
+#[derive(Component, Default, Clone, Copy, Hash, Debug, PartialEq, Eq)]
+pub struct FighterPresentationSnap(pub bool);
+
 #[derive(Component, Deref, DerefMut, Default, Clone, Copy, Hash)]
 #[require(FighterPreviousTranslation)]
 pub struct FighterTranslation(pub FGVec2);
@@ -52,10 +57,31 @@ pub fn sample_presentation_translation(
     }
 }
 
+pub fn sample_presentation_translation_with_snap(
+    previous: FighterPreviousTranslation,
+    current: FighterTranslation,
+    overstep_fraction: f32,
+    mode: PresentationMotionMode,
+    snapped: FighterPresentationSnap,
+) -> Vec2 {
+    if snapped.0 {
+        Vec2::new(current.x.to_num(), current.y.to_num())
+    } else {
+        sample_presentation_translation(previous, current, overstep_fraction, mode)
+    }
+}
+
+pub fn clear_fighter_presentation_snaps(mut fighters: Query<&mut FighterPresentationSnap>) {
+    for mut snap in &mut fighters {
+        snap.0 = false;
+    }
+}
+
 pub fn apply_fighter_translation_to_visuals(
     query: Query<(
         &FighterTranslation,
         &FighterPreviousTranslation,
+        &FighterPresentationSnap,
         &FighterHitstopShake,
         &mut Transform,
     )>,
@@ -64,12 +90,13 @@ pub fn apply_fighter_translation_to_visuals(
     game_settings: Res<GameSettings>,
 ) {
     let overstep_fraction = timing.overstep_fraction();
-    for (translation, previous_translation, hitstop_shake, mut transform) in query {
-        let translation = sample_presentation_translation(
+    for (translation, previous_translation, presentation_snap, hitstop_shake, mut transform) in query {
+        let translation = sample_presentation_translation_with_snap(
             *previous_translation,
             *translation,
             overstep_fraction,
             debug_settings.motion_sampling,
+            *presentation_snap,
         );
         transform.translation = Vec3::new(
             translation.x,
@@ -169,6 +196,19 @@ mod tests {
         assert_eq!(position, Vec2::new(7.0, 14.0));
     }
 
+    #[test]
+    fn presentation_translation_uses_current_sample_after_snap() {
+        let position = sample_presentation_translation_with_snap(
+            FighterPreviousTranslation(FGVec2::new(FGi32::lit("2"), FGi32::lit("4"))),
+            FighterTranslation(FGVec2::new(FGi32::lit("6"), FGi32::lit("12"))),
+            0.25,
+            PresentationMotionMode::Extrapolation,
+            FighterPresentationSnap(true),
+        );
+
+        assert_eq!(position, Vec2::new(6.0, 12.0));
+    }
+
     #[test]
     fn snapshot_fighter_motion_copies_current_world_state() {
         let mut world = World::new();

src/fighter/state/air.rs

@@ -123,6 +123,7 @@ pub fn collision_interrupt(
     ctx.ecb.left -= diff;
     ctx.ecb.right -= diff;
     ctx.translation.0 = res.hit_position;
+    ctx.presentation_snap.0 = true;
     ctx.surface.land(res.line_id);
     Some(FighterState::Land(LandingState::create(landing_type)))
 }

src/fighter/state/ground.rs

@@ -376,6 +376,7 @@ mod tests {
             right: FGVec2::lit("0.5", "0.0"),
         };
         let previous_ecb = FighterPreviousECB::from(ecb);
+        let mut presentation_snap = crate::fighter::FighterPresentationSnap::default();
         let mut context = CollisionContext {
             translation: &mut translation,
             prev_translation: &previous_translation,
@@ -386,6 +387,7 @@ mod tests {
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
             leave_ground_ecb_lock_duration: 10,
+            presentation_snap: &mut presentation_snap,
             downward_stick_threshold: FGi32::ONE,
         };
 
@@ -429,6 +431,7 @@ mod tests {
             right: FGVec2::lit("0.5", "0.0"),
         };
         let previous_ecb = FighterPreviousECB::from(ecb);
+        let mut presentation_snap = crate::fighter::FighterPresentationSnap::default();
         let mut context = CollisionContext {
             translation: &mut translation,
             prev_translation: &previous_translation,
@@ -439,6 +442,7 @@ mod tests {
             prev_ecb: &previous_ecb,
             stage_collision: &stage_collision,
             leave_ground_ecb_lock_duration: 10,
+            presentation_snap: &mut presentation_snap,
             downward_stick_threshold: FGi32::ONE,
         };
 

src/fighter/state/mod.rs

@@ -20,6 +20,7 @@ use crate::fighter::{
     Fighter, FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop,
     FighterHitstopShake, FighterHitstopShakeKind, FighterHitstopShakeRole,
     FighterPreviousTranslation, FighterSurfaceState, FighterTranslation, FighterVelocity,
+    FighterPresentationSnap,
 };
 use crate::fighter::surface::EcbLockPolicy;
 use crate::game_settings::GameSettings;
@@ -200,6 +201,7 @@ pub struct CollisionContext<'a> {
     pub prev_ecb: &'a FighterPreviousECB,
     pub stage_collision: &'a StageCollision,
     pub leave_ground_ecb_lock_duration: u32,
+    pub presentation_snap: &'a mut FighterPresentationSnap,
     pub downward_stick_threshold: FGi32,
 }
 
@@ -244,6 +246,7 @@ fighter_states! {
 pub struct FighterFrameQuery {
     pub translation: &'static mut FighterTranslation,
     pub prev_translation: &'static mut FighterPreviousTranslation,
+    pub presentation_snap: &'static mut FighterPresentationSnap,
     pub input: &'static mut FighterInput,
     pub hitboxes: &'static mut FighterHitboxes,
     pub velocity: &'static mut FighterVelocity,
@@ -354,6 +357,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
         CollisionContext {
             translation: &mut self.translation,
             prev_translation: &self.prev_translation,
+            presentation_snap: &mut self.presentation_snap,
             input: &self.input,
             velocity: &mut self.velocity,
             surface: &mut self.surface,