[Merged by Bors] - bevy_pbr: Fix tangent and normal normalization

crates/bevy_pbr/src/render/mesh_functions.wgsl

@@ -17,20 +17,36 @@ fn mesh_position_local_to_clip(model: mat4x4<f32>, vertex_position: vec4<f32>) -
 }
 
 fn mesh_normal_local_to_world(vertex_normal: vec3<f32>) -> vec3<f32> {
-    return mat3x3<f32>(
-        mesh.inverse_transpose_model[0].xyz,
-        mesh.inverse_transpose_model[1].xyz,
-        mesh.inverse_transpose_model[2].xyz
-    ) * vertex_normal;
+    // 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.
+    // http://www.mikktspace.com/
+    return normalize(
+        mat3x3<f32>(
+            mesh.inverse_transpose_model[0].xyz,
+            mesh.inverse_transpose_model[1].xyz,
+            mesh.inverse_transpose_model[2].xyz
+        ) * vertex_normal
+    );
 }
 
 fn mesh_tangent_local_to_world(model: mat4x4<f32>, vertex_tangent: vec4<f32>) -> vec4<f32> {
+    // 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.
+    // http://www.mikktspace.com/
     return vec4<f32>(
-        mat3x3<f32>(
-            model[0].xyz,
-            model[1].xyz,
-            model[2].xyz
-        ) * vertex_tangent.xyz,
+        normalize(
+            mat3x3<f32>(
+                model[0].xyz,
+                model[1].xyz,
+                model[2].xyz
+            ) * vertex_tangent.xyz
+        ),
         vertex_tangent.w
     );
 }

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -15,7 +15,13 @@ fn prepare_normal(
 #endif
     is_front: bool,
 ) -> vec3<f32> {
-    var N: vec3<f32> = normalize(world_normal);
+    // NOTE: The mikktspace method of normal mapping explicitly requires that the world normal NOT
+    // be re-normalized in the fragment shader. This is primarily to match the way mikktspace
+    // bakes vertex tangents and normal maps so that this is the exact inverse. 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.
+    // http://www.mikktspace.com/
+    var N: vec3<f32> = world_normal;
 
 #ifdef VERTEX_TANGENTS
 #ifdef STANDARDMATERIAL_NORMAL_MAP
@@ -236,7 +242,7 @@ fn pbr(
 fn tone_mapping(in: vec4<f32>) -> vec4<f32> {
     // tone_mapping
     return vec4<f32>(reinhard_luminance(in.rgb), in.a);
-    
+
     // Gamma correction.
     // Not needed with sRGB buffer
     // output_color.rgb = pow(output_color.rgb, vec3(1.0 / 2.2));