feat: add pbr support

destrum/assets_src/shaders/mesh.vert

@@ -8,7 +8,6 @@ layout (location = 0) out vec3 outPos;
 layout (location = 1) out vec2 outUV;
 layout (location = 2) out vec3 outNormal;
 layout (location = 3) out vec4 outTangent;
-layout (location = 4) out mat3 outTBN;
 
 // The depth pre-pass reuses this shader, positions have to match bit for bit
 // so the main pass can depth test against it with LESS_OR_EQUAL
@@ -29,10 +28,6 @@ void main()
     // outNormal = (pcs.transform * vec4(v.normal, 0.0)).xyz;
     outNormal = mat3(transpose(inverse(pcs.transform))) * v.normal;
 
-    outTangent = v.tangent;
-
-    vec3 T = normalize(vec3(pcs.transform * v.tangent));
-    vec3 N = normalize(outNormal);
-    vec3 B = cross(N, T) * v.tangent.w;
-    outTBN = mat3(T, B, N);
+    // w is the bitangent sign, the fragment shader builds the TBN from the interpolated vectors
+    outTangent = vec4(mat3(pcs.transform) * v.tangent.xyz, v.tangent.w);
 }