Add mechanism to ignore platforms (#63)

Reviewed-on: #63
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/collision.rs

@@ -44,6 +44,7 @@ pub fn air_collide_with_stage(
     prev_ecb: &FighterPreviousECB,
     ecb: &FighterECB,
     stage_collision: &StageCollision,
+    ignored_polys: &[usize],
 ) -> Option<AirCollisionWithStageResult> {
     let ray_segment = FGSegment2d::new(
         prev_translation.0 + prev_ecb.get_bottom_point(),
@@ -54,6 +55,7 @@ pub fn air_collide_with_stage(
         .stage_polys
         .iter()
         .enumerate()
+        .filter(|(poly_idx, _)| !ignored_polys.contains(poly_idx))
         .filter_map(|(poly_idx, poly)| {
             poly.intersect_ray(ray_segment).map(|intersect_result| {
                 (
@@ -76,3 +78,54 @@ pub fn air_collide_with_stage(
         .max_by(|(_, a), (_, b)| a.cmp(b))
         .map(|(result, _)| result)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::fighter::ecb::{FighterECB, FighterPreviousECB};
+    use crate::stage::line::{StagePoly, StagePolyLineSegmentType, StagePolyType};
+
+    fn horizontal_platform(y: &str) -> StagePoly {
+        StagePoly::build(
+            StagePolyType::Platform,
+            &[
+                (FGVec2::lit("-2", y), StagePolyLineSegmentType::Floor),
+                (FGVec2::lit("2", y), StagePolyLineSegmentType::Floor),
+            ],
+        )
+    }
+
+    #[test]
+    fn airborne_collision_skips_ignored_polygons() {
+        let stage_collision = StageCollision {
+            stage_polys: vec![horizontal_platform("0"), horizontal_platform("1")],
+        };
+        let previous_translation = FighterPreviousTranslation(FGVec2::lit("0", "2"));
+        let translation = FighterTranslation(FGVec2::lit("0", "-1"));
+        let previous_ecb = FighterPreviousECB {
+            bottom: FGVec2::ZERO,
+            top: FGVec2::ZERO,
+            left: FGVec2::ZERO,
+            right: FGVec2::ZERO,
+        };
+        let ecb = FighterECB {
+            bottom: FGVec2::ZERO,
+            top: FGVec2::ZERO,
+            left: FGVec2::ZERO,
+            right: FGVec2::ZERO,
+        };
+
+        let collision = air_collide_with_stage(
+            &previous_translation,
+            &translation,
+            &previous_ecb,
+            &ecb,
+            &stage_collision,
+            &[1],
+        )
+        .expect("the non-ignored platform should still be collidable");
+
+        assert_eq!(collision.line_id.polygon, 0);
+        assert_eq!(collision.hit_position, FGVec2::lit("0", "0"));
+    }
+}