bevy_pbr: Fix negation of normal for back-side when no normal map

bevyengine · Aug 22, 2022 · dbf9097 · dbf9097
1 parent 8025c0f
commit dbf9097
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Showing 3 changed files with 34 additions and 10 deletions.
diff --git a/assets/shaders/array_texture.wgsl b/assets/shaders/array_texture.wgsl
@@ -14,6 +14,7 @@ var my_array_texture: texture_2d_array<f32>;
 var my_array_texture_sampler: sampler;
 
 struct FragmentInput {
+    @builtin(front_facing) is_front: bool,
     @builtin(position) frag_coord: vec4<f32>,
     #import bevy_pbr::mesh_vertex_output
 };
@@ -33,13 +34,17 @@ fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
 
     pbr_input.frag_coord = in.frag_coord;
     pbr_input.world_position = in.world_position;
-    pbr_input.world_normal = in.world_normal;
+    pbr_input.world_normal = prepare_world_normal(
+        in.world_normal,
+        (material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u,
+        in.is_front,
+    );
 
     pbr_input.is_orthographic = view.projection[3].w == 1.0;
 
-    pbr_input.N = prepare_normal(
-        pbr_input.material.flags,
-        in.world_normal,
+    pbr_input.N = apply_normal_mapping(
+        material.flags,
+        pbr_input.world_normal,
 #ifdef VERTEX_TANGENTS
 #ifdef STANDARDMATERIAL_NORMAL_MAP
         in.world_tangent,

diff --git a/crates/bevy_pbr/src/render/pbr.wgsl b/crates/bevy_pbr/src/render/pbr.wgsl
@@ -9,6 +9,7 @@
 #import bevy_pbr::pbr_functions
 
 struct FragmentInput {
+    @builtin(front_facing) is_front: bool,
     @builtin(position) frag_coord: vec4<f32>,
     #import bevy_pbr::mesh_vertex_output
 };
@@ -68,13 +69,17 @@ fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
 
         pbr_input.frag_coord = in.frag_coord;
         pbr_input.world_position = in.world_position;
-        pbr_input.world_normal = in.world_normal;
+        pbr_input.world_normal = prepare_world_normal(
+            in.world_normal,
+            (material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u,
+            in.is_front,
+        );
 
         pbr_input.is_orthographic = view.projection[3].w == 1.0;
 
-        pbr_input.N = prepare_normal(
+        pbr_input.N = apply_normal_mapping(
             material.flags,
-            in.world_normal,
+            pbr_input.world_normal,
 #ifdef VERTEX_TANGENTS
 #ifdef STANDARDMATERIAL_NORMAL_MAP
             in.world_tangent,

diff --git a/crates/bevy_pbr/src/render/pbr_functions.wgsl b/crates/bevy_pbr/src/render/pbr_functions.wgsl
@@ -1,8 +1,22 @@
 #define_import_path bevy_pbr::pbr_functions
 
-// NOTE: This ensures that the world_normal is normalized and if
-// vertex tangents and normal maps then normal mapping may be applied.
-fn prepare_normal(
+fn prepare_world_normal(
+    world_normal: vec3<f32>,
+    double_sided: bool,
+    is_front: bool,
+) -> vec3<f32> {
+    var output: vec3<f32> = world_normal;
+#ifndef VERTEX_TANGENTS
+#ifndef STANDARDMATERIAL_NORMAL_MAP
+    // NOTE: When NOT using normal-mapping, if looking at the back face of a double-sided
+    // material, the normal needs to be inverted. This is a branchless version of that.
+    output = (f32(!double_sided || is_front) * 2.0 - 1.0) * output;
+#endif
+#endif
+    return output;
+}
+
+fn apply_normal_mapping(
     standard_material_flags: u32,
     world_normal: vec3<f32>,
 #ifdef VERTEX_TANGENTS