Fix ledge transitions and root motion loops (#91)

## Summary

- resolve each ledge action to the walkable segment on the stage-interior side
- preserve repeating root-motion displacement across every animation cycle
- add regression coverage for left/right ledge segments and multiple root-motion wraps
- Implement ledge intangibility

Reviewed-on: #91
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/baked_animation/mod.rs

@@ -487,7 +487,7 @@ mod tests {
     }
 
     #[test]
-    fn repeating_root_motion_preserves_cycle_displacement_at_wrap() {
+    fn repeating_root_motion_preserves_cycle_displacement_at_every_wrap() {
         let names = ["root".into()];
         let parents = [None];
         let pose = |x| FixedMat4::IDENTITY.with_translation(FGVec3::lit(x, "0", "0"));
@@ -498,7 +498,13 @@ mod tests {
             repeat: true,
         };
 
-        for (frame_number, x) in [(0, "0"), (1, "1")] {
+        for (frame_number, x, expected_delta) in [
+            (0, "0", FGVec3::ZERO),
+            (1, "1", FGVec3::lit("1", "0", "0")),
+            (2, "0", FGVec3::lit("1", "0", "0")),
+            (3, "1", FGVec3::lit("1", "0", "0")),
+            (4, "0", FGVec3::lit("1", "0", "0")),
+        ] {
             matrices.set_pose_with_frame(
                 frame(frame_number),
                 Some(0),
@@ -511,20 +517,8 @@ mod tests {
                 &[pose(x)],
                 FGi32::ONE,
             );
+            assert_eq!(matrices.root_motion_delta(), expected_delta);
         }
-        matrices.set_pose_with_frame(
-            frame(2),
-            Some(0),
-            Some(FGVec3::ZERO),
-            FGVec3::lit("2", "0", "0"),
-            Some(2),
-            AnimKind::Wait,
-            &names,
-            &parents,
-            &[pose("0")],
-            FGi32::ONE,
-        );
-        assert_eq!(matrices.root_motion_delta(), FGVec3::lit("1", "0", "0"));
     }
 
     #[test]

src/fighter/baked_animation/runtime.rs

@@ -110,6 +110,9 @@ impl BakedFighterAnimations {
             .get(&kind)
             .and_then(|index| self.clips.get(*index))
     }
+    pub fn get_animation_duration(&self, kind: AnimKind) -> Option<usize> {
+        self.clip(kind).map(|clip| clip.frames.len())
+    }
 }
 
 #[derive(Component, Clone, Debug, Default, Hash)]
@@ -411,7 +414,9 @@ impl FighterBoneMatrices {
                     previous.kind == animation_frame.kind
                         && previous.frame.saturating_add(1) == animation_frame.frame
                 })
-                && root_motion_loop_frame_count == Some(animation_frame.frame)
+                && root_motion_loop_frame_count.is_some_and(|loop_frame_count| {
+                    loop_frame_count > 0 && animation_frame.frame % loop_frame_count == 0
+                })
             {
                 delta = delta + root_motion_cycle_delta;
             }

src/fighter/state/ledge_action.rs

@@ -7,7 +7,7 @@ use crate::fighter::FighterFacingDirection;
 use crate::input::FighterCommands;
 use crate::math::int::FGi32;
 use crate::math::vec::FGVec2;
-use crate::stage::line::{StageLedgeSide, StageLineID, StageVertexID};
+use crate::stage::line::{StageLedgeSide, StageVertexID};
 
 #[derive(Debug, Clone, Hash)]
 pub enum LedgeAction {
@@ -96,17 +96,15 @@ impl FighterStateImpl for LedgeActionState {
             let normalized_root_position = FGVec2::new(normalized_root_position.x * ledge_modifier, normalized_root_position.y);
             
             if normalized_root_position.x.is_positive() && normalized_root_position.y.is_positive() {
-                self.is_in_grounded_phase = true;
-                
-                let segment_id = StageLineID {
-                    polygon: self.ledge_id.polygon,
-                    segment: self.ledge_id.vertex
-                };
-                let Some(poly) = state_context.stage_collision.get_segment(segment_id) else {
+                let Some((segment_id, _)) = state_context
+                    .stage_collision
+                    .find_ledge_ground_segment(self.ledge_id)
+                else {
                     return;
                 };
-                
-                state_context.translation.0 = poly.segment.point1();
+
+                self.is_in_grounded_phase = true;
+                state_context.translation.0 = ledge.position;
                 state_context.surface.land(segment_id);
             }
         }
@@ -136,4 +134,3 @@ impl FighterStateImpl for LedgeActionState {
         self.is_in_grounded_phase
     }
 }
-

src/fighter/state/ledge_wait.rs

@@ -3,9 +3,9 @@ use crate::fighter::animation::AnimKind;
 use crate::fighter::state::air::AirborneStateCommon;
 use crate::fighter::state::fall::FallState;
 use crate::fighter::state::FighterState;
-use crate::fighter::FighterFacingDirection;
 use crate::fighter::state::jump::JumpStateInitiator;
 use crate::fighter::state::ledge_action::{LedgeActionState};
+use crate::fighter::{FighterFacingDirection, FighterInvulnerabilityState};
 use crate::input::FighterCommands;
 use crate::math::vec::FGVec2;
 use crate::stage::line::{StageLedgeSide, StageVertexID};
@@ -58,6 +58,14 @@ 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.vulnerability = FighterInvulnerabilityState::Intangible {
+            frames_remaining: Some(
+                state_context
+                    .game_settings
+                    .fighter_common
+                    .ledge_grab_invulnerability_duration,
+            ),
+        };
         let Some(ledge) = state_context.stage_collision.find_ledge_by_vertex(self.ledge_id) else {
             return;
         };
@@ -127,4 +135,3 @@ fn is_ledge_drop_input(
 
     false
 }
-

src/fighter/state/mod.rs

@@ -195,6 +195,10 @@ impl EnterContext<'_> {
                 + animation_position_to_gameplay(position, self.facing_direction),
         )
     }
+
+    pub fn get_animation_duration(&self, kind: AnimKind) -> Option<usize> {
+        self.baked_animations.get_animation_duration(kind)
+    }
 }
 
 pub struct ExitContext<'a> {

src/game_settings.rs

@@ -52,6 +52,7 @@ pub struct FighterSettingsCommon {
     pub intangible_pulse_duration: u32,
 
     pub angel_platform_invulnerability_duration: u32,
+    pub ledge_grab_invulnerability_duration: u32,
 
     /// When hit while the receiver is in the air, use this angle
     pub sakurai_angle_aerial_angle: FGi32,

src/stage/line.rs

@@ -95,6 +95,32 @@ impl StageCollision {
         self.ledges.iter().find(|ledge| ledge.id == vertex)
     }
 
+    /// Returns the walkable segment on the stage side of a ledge.
+    pub fn find_ledge_ground_segment(
+        &self,
+        vertex: StageVertexID,
+    ) -> Option<(StageLineID, &StagePolyLineSegment)> {
+        let ledge = self.find_ledge_by_vertex(vertex)?;
+        let polygon = self.stage_polys.get(vertex.polygon)?;
+        let segment = match ledge.hang_side {
+            StageLedgeSide::Left => vertex.vertex,
+            StageLedgeSide::Right => {
+                if vertex.vertex > 0 {
+                    vertex.vertex - 1
+                } else if matches!(polygon.poly_type, StagePolyType::Closed) {
+                    polygon.segments.len().checked_sub(1)?
+                } else {
+                    return None;
+                }
+            }
+        };
+        let line_id = StageLineID {
+            polygon: vertex.polygon,
+            segment,
+        };
+        Some((line_id, polygon.get_segment(segment)?))
+    }
+
     pub fn get_segment(&self, segment: StageLineID) -> Option<&StagePolyLineSegment> {
         self.stage_polys.get(segment.polygon).map(|poly| poly.segments.get(segment.segment))?
     }

src/stage/manifest.rs

@@ -428,6 +428,7 @@ impl StageCameraProfile {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::stage::line::StageLineID;
 
     fn platform(ledges: Vec<StageLedgeDefinition>) -> StagePolyDefinition {
         StagePolyDefinition {
@@ -461,6 +462,35 @@ mod tests {
         assert_eq!(ledges[1].position, FGVec2::lit("5", "0"));
     }
 
+    #[test]
+    fn ledge_ground_segments_point_toward_the_stage_interior() {
+        let definition = platform(vec![
+            StageLedgeDefinition {
+                vertex: 0,
+                hang_side: StageLedgeSide::Left,
+            },
+            StageLedgeDefinition {
+                vertex: 1,
+                hang_side: StageLedgeSide::Right,
+            },
+        ]);
+        let collision = StageCollision {
+            stage_polys: vec![StagePoly::build(definition.poly_type, &definition.lines)],
+            ledges: definition.resolved_ledges(0).collect(),
+        };
+
+        for vertex in [0, 1] {
+            let (line_id, segment) = collision
+                .find_ledge_ground_segment(StageVertexID { polygon: 0, vertex })
+                .unwrap();
+            assert_eq!(line_id, StageLineID { polygon: 0, segment: 0 });
+            assert!(matches!(
+                segment.segment_type,
+                StagePolyLineSegmentType::Floor
+            ));
+        }
+    }
+
     #[test]
     fn invalid_and_duplicate_ledge_vertices_are_rejected() {
         let missing = platform(vec![StageLedgeDefinition {