Revert "bevy_pbr: Fix tangent and normal normalization (bevyengine#5666)"

This reverts commit 681c9c6.

Author: HackerFoo

crates/bevy_pbr/src/render/mesh.rs

@@ -18,7 +18,7 @@ use bevy_ecs::{
     query::ROQueryItem,
     system::{lifetimeless::*, SystemParamItem, SystemState},
 };
-use bevy_math::{Mat3A, Mat4, Vec2};
+use bevy_math::{Mat4, Vec2};
 use bevy_reflect::TypeUuid;
 use bevy_render::{
     extract_component::{ComponentUniforms, DynamicUniformIndex, UniformComponentPlugin},
@@ -134,9 +134,6 @@ bitflags::bitflags! {
     #[repr(transparent)]
     struct MeshFlags: u32 {
         const SHADOW_RECEIVER            = (1 << 0);
-        // Indicates the sign of the determinant of the 3x3 model matrix. If the sign is positive,
-        // then the flag should be set, else it should not be set.
-        const SIGN_DETERMINANT_MODEL_3X3 = (1 << 31);
         const NONE                       = 0;
         const UNINITIALIZED              = 0xFFFF;
     }
@@ -167,14 +164,11 @@ pub fn extract_meshes(
     {
         let transform = transform.compute_matrix();
         let previous_transform = previous_transform.map(|t| t.0).unwrap_or(transform);
-        let mut flags = if not_receiver.is_some() {
+        let flags = if not_receiver.is_some() {
             MeshFlags::empty()
         } else {
             MeshFlags::SHADOW_RECEIVER
         };
-        if Mat3A::from_mat4(transform).determinant().is_sign_positive() {
-            flags |= MeshFlags::SIGN_DETERMINANT_MODEL_3X3;
-        }
         let uniform = MeshUniform {
             flags: flags.bits,
             transform,

crates/bevy_pbr/src/render/mesh_functions.wgsl

@@ -17,47 +17,20 @@ 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> {
-    // 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
-    );
-}
-
-// Calculates the sign of the determinant of the 3x3 model matrix based on a
-// mesh flag
-fn sign_determinant_model_3x3() -> f32 {
-    // bool(u32) is false if 0u else true
-    // f32(bool) is 1.0 if true else 0.0
-    // * 2.0 - 1.0 remaps 0.0 or 1.0 to -1.0 or 1.0 respectively
-    return f32(bool(mesh.flags & MESH_FLAGS_SIGN_DETERMINANT_MODEL_3X3_BIT)) * 2.0 - 1.0;
+    return 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>(
-        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_3x3()
+        mat3x3<f32>(
+            model[0].xyz,
+            model[1].xyz,
+            model[2].xyz
+        ) * vertex_tangent.xyz,
+        vertex_tangent.w
     );
 }

crates/bevy_pbr/src/render/mesh_types.wgsl

@@ -15,5 +15,3 @@ struct SkinnedMesh {
 #endif
 
 const MESH_FLAGS_SHADOW_RECEIVER_BIT: u32 = 1u;
-// 2^31 - if the flag is set, the sign is positive, else it is negative
-const MESH_FLAGS_SIGN_DETERMINANT_MODEL_3X3_BIT: u32 = 2147483648u;

crates/bevy_pbr/src/render/pbr_functions.wgsl

@@ -55,13 +55,7 @@ fn apply_normal_mapping(
     uv: vec2<f32>,
 #endif
 ) -> vec3<f32> {
-    // 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;
+    var N: vec3<f32> = normalize(world_normal);
 
 #ifdef VERTEX_TANGENTS
 #ifdef STANDARDMATERIAL_NORMAL_MAP