From da3ab52fe057ec87cc8e341b88d8b2c595c2fccd Mon Sep 17 00:00:00 2001
From: Quaternions <krakow20@gmail.com>
Date: Tue, 13 May 2025 15:22:28 -0700
Subject: [PATCH] physics: do not require complete_mesh as first submesh This
 removes a silent assumption about the input meshes and moves the branching
 from submeshes() to complete_mesh()

---
 engine/physics/src/model.rs   | 40 ++++++++++++++++++++---------------
 engine/physics/src/physics.rs |  2 +-
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/engine/physics/src/model.rs b/engine/physics/src/model.rs
index 9c9ab035..bddb094d 100644
--- a/engine/physics/src/model.rs
+++ b/engine/physics/src/model.rs
@@ -143,10 +143,12 @@ impl From<MeshId> for PhysicsMeshId{
 pub struct PhysicsSubmeshId(u32);
 pub struct PhysicsMesh{
 	data:PhysicsMeshData,
-	complete_mesh:PhysicsMeshTopology,
-	//Most objects in roblox maps are already convex, so the list length is 0
-	//as soon as the mesh is divided into 2 submeshes, the list length jumps to 2.
-	//length 1 is unnecessary since the complete mesh would be a duplicate of the only submesh, but would still function properly
+	// The complete mesh is unused at this time.
+	// complete_mesh:PhysicsMeshTopology,
+	// Submeshes are guaranteed to be convex and may contain
+	// "virtual" faces which are not part of the complete mesh.
+	// Physics calculations should never resolve to hitting
+	// a virtual face.
 	submeshes:Vec<PhysicsMeshTopology>,
 }
 impl PhysicsMesh{
@@ -210,19 +212,24 @@ impl PhysicsMesh{
 		};
 		Self{
 			data,
-			complete_mesh:mesh_topology,
-			submeshes:Vec::new(),
+			// complete_mesh:mesh_topology.clone(),
+			submeshes:vec![mesh_topology],
 		}
 	}
 	pub fn unit_cylinder()->Self{
 		Self::unit_cube()
 	}
 	#[inline]
-	pub const fn complete_mesh(&self)->&PhysicsMeshTopology{
-		&self.complete_mesh
+	pub fn complete_mesh(&self)->&PhysicsMeshTopology{
+		// If there is exactly one submesh, then the complete mesh is identical to it.
+		if self.submeshes.len()==1{
+			self.submeshes.first().unwrap()
+		}else{
+			panic!("PhysicsMesh complete mesh is not known");
+		}
 	}
 	#[inline]
-	pub const fn complete_mesh_view(&self)->PhysicsMeshView{
+	pub fn complete_mesh_view(&self)->PhysicsMeshView{
 		PhysicsMeshView{
 			data:&self.data,
 			topology:self.complete_mesh(),
@@ -230,12 +237,7 @@ impl PhysicsMesh{
 	}
 	#[inline]
 	pub fn submeshes(&self)->&[PhysicsMeshTopology]{
-		//the complete mesh is already a convex mesh when len()==0, len()==1 is invalid but will still work
-		if self.submeshes.len()==0{
-			std::slice::from_ref(&self.complete_mesh)
-		}else{
-			&self.submeshes.as_slice()
-		}
+		&self.submeshes
 	}
 	#[inline]
 	pub fn submesh_view(&self,submesh_id:PhysicsSubmeshId)->PhysicsMeshView{
@@ -313,6 +315,10 @@ impl TryFrom<&model::Mesh> for PhysicsMesh{
 		if mesh.unique_pos.len()==0{
 			return Err(PhysicsMeshError::ZeroVertices);
 		}
+		// An empty physics mesh is a waste of resources
+		if mesh.physics_groups.len()==0{
+			return Err(PhysicsMeshError::NoPhysicsGroups);
+		}
 		let verts=mesh.unique_pos.iter().copied().map(Vert).collect();
 		//TODO: fix submeshes
 		//flat map mesh.physics_groups[$1].groups.polys()[$2] as face_id
@@ -320,7 +326,7 @@ impl TryFrom<&model::Mesh> for PhysicsMesh{
 		//the same face is not allowed to be in multiple polygon groups
 		let mut faces=Vec::new();
 		let mut face_id_from_face=HashMap::new();
-		let mut mesh_topologies:Vec<PhysicsMeshTopology>=mesh.physics_groups.iter().map(|physics_group|{
+		let mesh_topologies:Vec<PhysicsMeshTopology>=mesh.physics_groups.iter().map(|physics_group|{
 			//construct submesh
 			let mut submesh_faces=Vec::new();//these contain a map from submeshId->meshId
 			let mut submesh_verts=Vec::new();
@@ -416,7 +422,7 @@ impl TryFrom<&model::Mesh> for PhysicsMesh{
 				faces,
 				verts,
 			},
-			complete_mesh:mesh_topologies.pop().ok_or(PhysicsMeshError::NoPhysicsGroups)?,
+			// complete_mesh:None,
 			submeshes:mesh_topologies,
 		})
 	}
diff --git a/engine/physics/src/physics.rs b/engine/physics/src/physics.rs
index eee9d862..cdc176f0 100644
--- a/engine/physics/src/physics.rs
+++ b/engine/physics/src/physics.rs
@@ -417,7 +417,7 @@ impl HitboxMesh{
 		}
 	}
 	#[inline]
-	const fn transformed_mesh(&self)->TransformedMesh{
+	fn transformed_mesh(&self)->TransformedMesh{
 		TransformedMesh::new(self.mesh.complete_mesh_view(),&self.transform)
 	}
 }