From 5f743f46fc2db31bb7d48b8e2f4dd09fbb9111d9 Mon Sep 17 00:00:00 2001
From: Zicklag <zicklag@katharostech.com>
Date: Thu, 9 Mar 2023 19:26:10 -0600
Subject: [PATCH] fix: fix incorrect ground state detection when intersecting
 jump-through tiles. (#708)

Closes: #705
---
 core/src/physics.rs            | 34 ++++++++++++++++++++++++++++++----
 core/src/physics/collisions.rs | 11 ++++++++++-
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/core/src/physics.rs b/core/src/physics.rs
index dab90db441..0a653dd202 100644
--- a/core/src/physics.rs
+++ b/core/src/physics.rs
@@ -218,16 +218,42 @@ fn update_kinematic_bodies(
         // Check ground collision
         {
             let mut transform = transforms.get(entity).copied().unwrap();
+
+            // Don't get stuck floating in fall-through platforms
+            if body.velocity == Vec2::ZERO
+                && collision_world.tile_collision_filtered(transform, body.shape, |ent| {
+                    collision_world
+                        .tile_collision_kinds
+                        .get(ent)
+                        .map(|x| *x == TileCollisionKind::JumpThrough)
+                        .unwrap_or(false)
+                }) == TileCollisionKind::JumpThrough
+            {
+                body.fall_through = true;
+            }
+
+            // Move transform check down 1 slightly
             transform.translation.y -= 0.1;
 
             body.was_on_ground = body.is_on_ground;
 
-            let tile = collision_world.tile_collision(transform, body.shape);
+            let collider = collision_world.get_collider(entity);
+
+            let tile = collision_world.tile_collision_filtered(transform, body.shape, |ent| {
+                if collider.seen_wood {
+                    collision_world
+                        .tile_collision_kinds
+                        .get(ent)
+                        .map(|x| *x != TileCollisionKind::JumpThrough)
+                        .unwrap_or(false)
+                } else {
+                    true
+                }
+            });
 
             let on_jump_through_tile = tile == TileCollisionKind::JumpThrough;
-            body.is_on_ground = tile != TileCollisionKind::Empty
-                && !collision_world.get_collider(entity).seen_wood
-                && !(on_jump_through_tile && body.fall_through);
+            body.is_on_ground =
+                tile != TileCollisionKind::Empty && !(on_jump_through_tile && body.fall_through);
             body.is_on_platform = body.is_on_ground && on_jump_through_tile;
         }
 
diff --git a/core/src/physics/collisions.rs b/core/src/physics/collisions.rs
index f50bc04d23..18590920b3 100644
--- a/core/src/physics/collisions.rs
+++ b/core/src/physics/collisions.rs
@@ -870,6 +870,15 @@ impl<'a> CollisionWorld<'a> {
     /// Get the [`TileCollisionKind`] of the first tile detected colliding with the `shape` at the
     /// given `transform`.
     pub fn tile_collision(&self, transform: Transform, shape: ColliderShape) -> TileCollisionKind {
+        self.tile_collision_filtered(transform, shape, |_| true)
+    }
+
+    pub fn tile_collision_filtered(
+        &self,
+        transform: Transform,
+        shape: ColliderShape,
+        filter: impl Fn(Entity) -> bool,
+    ) -> TileCollisionKind {
         self.ctx
             .query_pipeline
             .intersection_with_shape(
@@ -883,7 +892,7 @@ impl<'a> CollisionWorld<'a> {
                 &*shape.shared_shape(),
                 rapier::QueryFilter::new().predicate(&|_handle, collider| {
                     let ent = RapierUserData::entity(collider.user_data);
-                    self.tile_collision_kinds.contains(ent)
+                    self.tile_collision_kinds.contains(ent) && filter(ent)
                 }),
             )
             .map(|x| RapierUserData::entity(self.ctx.collider_set.get(x).unwrap().user_data))