What is the correct approach to creating UberShader using function_constants in Metal?

Question

I just found out about function_constants in the WWDC 2016 What's New in Metal video and he mentioned UberShaders quite a few times. I want to create a uber shader fragment that can be used for different types of passes, such as simplePassThrough, defferred, etc. Below I want to use it.

constant int passType [[function_constant(0)]];
constant bool simplePassThrough = (passType == 0);
constant bool forwardShading = (passType == 1);
constant bool deferredShading = (passType == 2);

fragment FragmentOutStruct UberFragmentShader()
{
FragmentOutputStruct frgOut;
if (simplePassThrough) {
    // Update frgOut
} else if (forwardShading) {
    // Update frgOut
} else if (deferredShading) {
    // Update frgOut
}
return frgOut;
}

Is this the right approach? Will my last compiled MTLFunction see too many branches if I use this approach?

Answer 1

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Answer 2

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fragment FragmentOutStruct UberFragmentShader() {
    FragmentOutputStruct frgOut;
    // Update frgOut per `if (forwardShading)` chunk of original shader source
    return frgOut;
}

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