Metallic & Specular shader color is black on mobile platform

[Kushulain]

• Unity 2021.3.1f1
• built in render pipeline
• Android platform build settings
• "ProjectSettings->Graphics->Standard Shader Quality" is set to "low".

Problem:

Metallic & Specular shader appear with a black diffuse color.

Reproduce:

• Set "ProjectSettings->Graphics->Standard Shader Quality" to "low".
• Test any 3D model which use metallic or specular setup gltf shader.
• Color is black

Technical details:

When mobile platform is set in build settings, usually "Standard Shader Quality" is set to "low". ProjectSettings->Graphics->Standard Shader Quality It enables UNITY_NO_FULL_STANDARD_SHADER keyword, which makes ForwardSimple shader feature to be use. So then VertexOutputBaseSimple vertForwardBaseSimple (VertexInput v) is used (glTFUnityStandardCoreForwardSimple.cginc) But this function has a problem, it set the o.color BEFORE intialize o.color to zero. Resulting on diffuse color looking black.

Solution:

in the function VertexOutputBaseSimple vertForwardBaseSimple (VertexInput v) inside "glTFUnityStandardCoreForwardSimple.cginc". move the following code to the end of the function after UNITY_INITIALIZE_OUTPUT(VertexOutputBaseSimple, o);

#ifdef UNITY_COLORSPACE_GAMMA
    o.color.rgb = LinearToGammaSpace(v.color.rgb);
    o.color.a = v.color.a;
#else
    o.color = v.color;
#endif