Normalize only nonzero normals for mikktspace normal maps

crates/bevy_pbr/src/render/mesh_functions.wgsl

@@ -35,15 +35,20 @@ fn mesh_normal_local_to_world(vertex_normal: vec3<f32>, instance_index: u32) ->
     // NOTE: The mikktspace method of normal mapping requires that the world normal is
     // re-normalized in the vertex shader to match the way mikktspace bakes vertex tangents
     // and normal maps so that the exact inverse process is applied when shading. Blender, Unity,
-    // Unreal Engine, Godot, and more all use the mikktspace method. Do not change this code
-    // unless you really know what you are doing.
+    // Unreal Engine, Godot, and more all use the mikktspace method.
+    // We only skip normalization for invalid normals so that they don't become NaN.
+    // Do not change this code unless you really know what you are doing.
     // http://www.mikktspace.com/
-    return normalize(
-        mat2x4_f32_to_mat3x3_unpack(
-            mesh[instance_index].inverse_transpose_model_a,
-            mesh[instance_index].inverse_transpose_model_b,
-        ) * vertex_normal
-    );
+    if any(vertex_normal != vec3<f32>(0.0)) {
+        return normalize(
+            mat2x4_f32_to_mat3x3_unpack(
+                mesh[instance_index].inverse_transpose_model_a,
+                mesh[instance_index].inverse_transpose_model_b,
+            ) * vertex_normal
+        );
+    } else {
+        return vertex_normal;
+    }
 }
 
 // Calculates the sign of the determinant of the 3x3 model matrix based on a
@@ -59,19 +64,24 @@ fn mesh_tangent_local_to_world(model: mat4x4<f32>, vertex_tangent: vec4<f32>, in
     // NOTE: The mikktspace method of normal mapping requires that the world tangent is
     // re-normalized in the vertex shader to match the way mikktspace bakes vertex tangents
     // and normal maps so that the exact inverse process is applied when shading. Blender, Unity,
-    // Unreal Engine, Godot, and more all use the mikktspace method. Do not change this code
-    // unless you really know what you are doing.
+    // Unreal Engine, Godot, and more all use the mikktspace method.
+    // We only skip normalization for invalid tangents so that they don't become NaN.
+    // Do not change this code unless you really know what you are doing.
     // http://www.mikktspace.com/
-    return vec4<f32>(
-        normalize(
-            mat3x3<f32>(
-                model[0].xyz,
-                model[1].xyz,
-                model[2].xyz
-            ) * vertex_tangent.xyz
-        ),
-        // NOTE: Multiplying by the sign of the determinant of the 3x3 model matrix accounts for
-        // situations such as negative scaling.
-        vertex_tangent.w * sign_determinant_model_3x3m(instance_index)
-    );
+    if any(vertex_tangent != vec4<f32>(0.0)) {
+        return vec4<f32>(
+            normalize(
+                mat3x3<f32>(
+                    model[0].xyz,
+                    model[1].xyz,
+                    model[2].xyz
+                ) * vertex_tangent.xyz
+            ),
+            // NOTE: Multiplying by the sign of the determinant of the 3x3 model matrix accounts for
+            // situations such as negative scaling.
+            vertex_tangent.w * sign_determinant_model_3x3m(instance_index)
+        );
+    } else {
+        return vertex_tangent;
+    }
 }