Hi shader gurus, I'm writing a HLSL editor and I need to clear up some confusion...

1) As I understand it, a shader 'fallback' is when the graphics card doesn't support the required shader model, and so it uses a 'lower' version of the shader.

I am currently allowing the user to build different versions eg, model 1.1, 2.0, 3.0 etc.

How do I chain these fallbacks together in HLSL?

2) Are the shader inputs/outputs consistent among all versions of the shader.

Eg, if the shader for model 2.0, takes in TEXCOORDs, does that mean that the shader for version 1.1, must also use this? Or can they vary.

I might seem like I'm talking rubbish, but I need to get this straight so my editor works correctly.

Thanks