fixme

The physics algorithm expects vertices to align exactly with faces.  Since the face normal is calculated via the cross product of vertex positions, this allows the face normals to be exact with respect to the vertex positions.

engine/physics/src/model.rs

@@ -314,6 +314,9 @@ impl TryFrom<&model::Mesh> for PhysicsMesh{
 			return Err(PhysicsMeshError::ZeroVertices);
 		}
 		let verts=mesh.unique_pos.iter().copied().map(Vert).collect();
+		// TODO: do not hash faces to get face id
+		// meshes can have multiple identical nd representations while still being distinct faces,
+		// especially when the complete mesh is a non-convex mesh.
 		//TODO: fix submeshes
 		//flat map mesh.physics_groups[$1].groups.polys()[$2] as face_id
 		//lower face_id points to upper face_id

lib/bsp_loader/src/brush.rs

@@ -1,5 +1,5 @@
-use strafesnet_common::integer::Planar64;
-use strafesnet_common::{model,integer};
+use strafesnet_common::integer::{self,Planar64,Planar64Vec3};
+use strafesnet_common::model::{self,VertexId};
 use strafesnet_common::integer::{vec3::Vector3,Fixed,Ratio};
 
 use crate::{valve_transform_normal,valve_transform_dist};
@@ -138,7 +138,15 @@ fn planes_to_faces(face_list:std::collections::HashSet<Face>)->Result<Faces,Plan
 		loop{
 			// push point onto vertices
 			// problem: this may push a vertex that does not fit in the fixed point range and is thus meaningless
-			face.push(intersection.divide().narrow_1().unwrap());
+			//
+			// physics bug 2 originates from vertices being imprecise?
+			//
+			// Mask off the most precise 16 bits so that
+			// when face normals are calculated from
+			// the remaining 16 fractional bits
+			// they never exceed 32 bits of precision.
+			const MASK:Planar64=Planar64::raw(!((1<<16)-1));
+			face.push(intersection.divide().narrow_1().unwrap().map(|c|c&MASK));
 
 			// we looped back around to face1, we're done!
 			if core::ptr::eq(face1,face2){
@@ -204,6 +212,33 @@ impl std::fmt::Display for BrushToMeshError{
 }
 impl core::error::Error for BrushToMeshError{}
 
+fn subdivide_max_area(tris:&mut Vec<Vec<VertexId>>,cw_verts:&[(VertexId,Planar64Vec3)],i0:usize,i2:usize,id0:VertexId,id2:VertexId,v0:Planar64Vec3,v2:Planar64Vec3){
+	if i0+1==i2{
+		return;
+	}
+	let mut best_i1=i0+1;
+	if i0+2<i2{
+		let mut best_area={
+			let (_,v1)=cw_verts[best_i1.rem_euclid(cw_verts.len())];
+			(v2-v0).cross(v1-v0).length_squared()
+		};
+		for i1 in i0+2..=i2-1{
+			let (_,v1)=cw_verts[i1.rem_euclid(cw_verts.len())];
+			let area=(v2-v0).cross(v1-v0).length_squared();
+			if best_area<area{
+				best_i1=i1;
+				best_area=area;
+			}
+		}
+	}
+	let i1=best_i1;
+	let (id1,v1)=cw_verts[i1.rem_euclid(cw_verts.len())];
+	// draw max area first
+	tris.push(vec![id0,id1,id2]);
+	subdivide_max_area(tris,cw_verts,i0,i1,id0,id1,v0,v1);
+	subdivide_max_area(tris,cw_verts,i1,i2,id1,id2,v1,v2);
+}
+
 pub fn faces_to_mesh(faces:Vec<Vec<integer::Planar64Vec3>>)->model::Mesh{
 	// generate the mesh
 	let mut mb=model::MeshBuilder::new();
@@ -212,16 +247,34 @@ pub fn faces_to_mesh(faces:Vec<Vec<integer::Planar64Vec3>>)->model::Mesh{
 	// normals are ignored by physics
 	let normal=mb.acquire_normal_id(integer::vec3::ZERO);
 
-	let polygon_list=faces.into_iter().map(|face|{
-		face.into_iter().map(|pos|{
-			let pos=mb.acquire_pos_id(pos);
-			mb.acquire_vertex_id(model::IndexedVertex{
+	let polygon_list=faces.into_iter().flat_map(|face|{
+		let cw_verts=face.into_iter().map(|position|{
+			let pos=mb.acquire_pos_id(position);
+			(mb.acquire_vertex_id(model::IndexedVertex{
 				pos,
 				tex,
 				normal,
 				color,
-			})
-		}).collect()
+			}),position)
+		}).collect::<Vec<_>>();
+
+		// scan and select maximum area triangle O(n^3)
+		let len=cw_verts.len();
+		let cw_verts=cw_verts.as_slice();
+		let ((i0,i1,i2),(v0,v1,v2))=cw_verts[..len-2].iter().enumerate().flat_map(|(i0,&(_,v0))|
+			cw_verts[i0+1..len-1].iter().enumerate().flat_map(move|(i1,&(_,v1))|
+				cw_verts[i0+i1+2..].iter().enumerate().map(move|(i2,&(_,v2))|((i0,i0+i1+1,i0+i1+i2+2),(v0,v1,v2)))
+			)
+		).max_by_key(|&(_,(v0,v1,v2))|(v2-v0).cross(v1-v0).length_squared()).unwrap();
+		// scan and select more maximum area triangles n * O(n)
+		let mut tris=Vec::with_capacity(len-2);
+		// da big one
+		let (id0,id1,id2)=(cw_verts[i0].0,cw_verts[i1].0,cw_verts[i2].0);
+		tris.push(vec![id0,id1,id2]);
+		subdivide_max_area(&mut tris,cw_verts,i0,i1,id0,id1,v0,v1);
+		subdivide_max_area(&mut tris,cw_verts,i1,i2,id1,id2,v1,v2);
+		subdivide_max_area(&mut tris,cw_verts,i2,i0+len,id2,id0,v2,v0);
+		tris
 	}).collect();
 
 	let polygon_groups=vec![model::PolygonGroup::PolygonList(model::PolygonList::new(polygon_list))];