From 9b3a9ce43785993eea3139ccd628a286e6809710 Mon Sep 17 00:00:00 2001
From: Rhys Lloyd <krakow20@gmail.com>
Date: Tue, 16 Dec 2025 12:24:04 -0800
Subject: [PATCH] narrow directions more carefully

---
 engine/physics/src/minimum_difference.rs | 55 ++++++++++++++++++------
 1 file changed, 43 insertions(+), 12 deletions(-)

diff --git a/engine/physics/src/minimum_difference.rs b/engine/physics/src/minimum_difference.rs
index b63d3e4e..9a8217fd 100644
--- a/engine/physics/src/minimum_difference.rs
+++ b/engine/physics/src/minimum_difference.rs
@@ -100,6 +100,37 @@ const fn choose_any_direction()->Planar64Vec3{
 	vec3::X
 }
 
+fn narrow_dir2(dir:Vector3<Fixed<2,64>>)->Planar64Vec3{
+	if dir==vec3::zero(){
+		return dir.narrow_1().unwrap();
+	}
+	let x=dir.x.as_bits().unsigned_abs().bits();
+	let y=dir.y.as_bits().unsigned_abs().bits();
+	let z=dir.z.as_bits().unsigned_abs().bits();
+	let big=x.max(y).max(z);
+	const MAX_BITS:u32=64+31;
+	if MAX_BITS<big{
+		dir>>(big-MAX_BITS)
+	}else{
+		dir
+	}.narrow_1().unwrap()
+}
+fn narrow_dir3(dir:Vector3<Fixed<3,96>>)->Planar64Vec3{
+	if dir==vec3::zero(){
+		return dir.narrow_1().unwrap();
+	}
+	let x=dir.x.as_bits().unsigned_abs().bits();
+	let y=dir.y.as_bits().unsigned_abs().bits();
+	let z=dir.z.as_bits().unsigned_abs().bits();
+	let big=x.max(y).max(z);
+	const MAX_BITS:u32=96+31;
+	if MAX_BITS<big{
+		dir>>(big-MAX_BITS)
+	}else{
+		dir
+	}.narrow_1().unwrap()
+}
+
 fn reduce1<M:MeshQuery>(
 	[v0]:Simplex<1,M::Vert>,
 	mesh:&M,
@@ -165,7 +196,7 @@ fn reduce2<M:MeshQuery>(
 		// -- modify the direction to take into account a0R and b0R
 		// return direction, a0, a1, b0, b1
 		return Reduced{
-			dir:direction.narrow_1().unwrap(),
+			dir:narrow_dir3(direction),
 			simplex:Simplex1_3::Simplex2([v0,v1]),
 		};
 	}
@@ -231,7 +262,7 @@ fn reduce3<M:MeshQuery>(
 
 		// return direction, a0, a1, b0, b1, c0, c1
 		return Reduced{
-			dir:direction.narrow_1().unwrap(),
+			dir:narrow_dir2(direction),
 			simplex:Simplex1_3::Simplex3([v0,v1,v2]),
 		};
 	}
@@ -265,14 +296,14 @@ fn reduce3<M:MeshQuery>(
 		if direction==vec3::zero(){
 			// direction = uv
 			return Reduced{
-				dir:uv.narrow_1().unwrap(),
+				dir:narrow_dir2(uv),
 				simplex:Simplex1_3::Simplex2([v0,v1]),
 			};
 		}
 
 		// return direction, a0, a1, b0, b1
 		return Reduced{
-			dir:direction.narrow_1().unwrap(),
+			dir:narrow_dir3(direction),
 			simplex:Simplex1_3::Simplex2([v0,v1]),
 		};
 	}
@@ -283,7 +314,7 @@ fn reduce3<M:MeshQuery>(
 	if dir==vec3::zero(){
 		// direction = uv
 		return Reduced{
-			dir:uv.narrow_1().unwrap(),
+			dir:narrow_dir2(uv),
 			simplex:Simplex1_3::Simplex1([v0]),
 		};
 	}
@@ -399,12 +430,12 @@ fn reduce4<M:MeshQuery>(
 		// return direction, a0, a1, b0, b1, c0, c1
 		if uv_w.is_negative(){
 			return Reduce::Reduced(Reduced{
-				dir:uv.narrow_1().unwrap(),
+				dir:narrow_dir2(uv),
 				simplex:Simplex1_3::Simplex3([v0,v1,v2]),
 			});
 		}else{
 			return Reduce::Reduced(Reduced{
-				dir:-uv.narrow_1().unwrap(),
+				dir:narrow_dir2(-uv),
 				simplex:Simplex1_3::Simplex3([v0,v1,v2]),
 			});
 		}
@@ -441,12 +472,12 @@ fn reduce4<M:MeshQuery>(
 			// return direction, a0, a1, b0, b1
 			if uv_w.is_negative(){
 				return Reduce::Reduced(Reduced{
-					dir:uv.narrow_1().unwrap(),
+					dir:narrow_dir2(uv),
 					simplex:Simplex1_3::Simplex2([v0,v1]),
 				});
 			}else{
 				return Reduce::Reduced(Reduced{
-					dir:-uv.narrow_1().unwrap(),
+					dir:narrow_dir2(-uv),
 					simplex:Simplex1_3::Simplex2([v0,v1]),
 				});
 			}
@@ -454,7 +485,7 @@ fn reduce4<M:MeshQuery>(
 
 		// return direction, a0, a1, b0, b1
 		return Reduce::Reduced(Reduced{
-			dir:direction.narrow_1().unwrap(),
+			dir:narrow_dir3(direction),
 			simplex:Simplex1_3::Simplex2([v0,v1]),
 		});
 	}
@@ -466,12 +497,12 @@ fn reduce4<M:MeshQuery>(
 		// direction = uvw < 0 and uv or -uv
 		if uv_w.is_negative(){
 			return Reduce::Reduced(Reduced{
-				dir:uv.narrow_1().unwrap(),
+				dir:narrow_dir2(uv),
 				simplex:Simplex1_3::Simplex1([v0]),
 			});
 		}else{
 			return Reduce::Reduced(Reduced{
-				dir:-uv.narrow_1().unwrap(),
+				dir:narrow_dir2(-uv),
 				simplex:Simplex1_3::Simplex1([v0]),
 			});
 		}