Conditional Defines and HLSL

Question

Is it possible to use project level conditional defines in hlsl code?

I'm trying to conditionaly compile a shader using MonoGame Content Procesor. Depending on project type (ie. Windows, Windows8...) different shader models should be used. Pragma directives are supported. The code:

#if WINDOWS 
   PixelShader = compile ps_3_0 PixelShaderFunction();
#else 
   ...

... doesn't work as WINDOWS is interpreted as false. Judging from the article on Gamasutra this should work. This answer on Gamedev lists constants which should be defined when using MonoGame.

I've also tried adding constants into csproj manually (in content project, then in dummy content compiler csproj).

Is there something I'm missing?

My sln structure is as follows:

1. MonoGameContentProject - holds .fx file
2. MonoGameDummyProject - has content reference to content project, builds .fx file
3. WindowsProject - has a link to dummy project xnb file in the windows build directory

Answer 1

Mono should behave the same way as .Net and the MSDN has this to say on preprocessor instructions ...

When the C# compiler encounters an #if directive, followed eventually by an #endif directive, it will compile the code between the directives only if the specified symbol is defined. Unlike C and C++, you cannot assign a numeric value to a symbol; the #if statement in C# is Boolean and only tests whether the symbol has been defined or not.

So it may be that the #define WINDOWS definition has not been made yet. I'm looking to see if I can find something useful on this.

Interesting secondary point but not really what you are after ...

https://stackoverflow.com/questions/473354/quote-needed-preprocessor-usage-is-bad-oo-practice

Could you perhaps take another approach?

Possible solution: Your syntax may not be quite right try something like this ...

#if (WINDOWS)
  // some WINDOWS-specific code here
#endif

EDIT: In light of my missing the fact that this is a shader problem I figured I should add this ...

Conditional defines based on environments are only possible on the CPU, to have such differences in shaders you need to create different versions of your shaders then conditionally choose them in your CPU code in which situation the above syntax should work.

In short: such preprocessor instructions are not possible in shader code.

Answer 2

I don't think you can directly, but you might consider writing a simple preprocessor and creating a custom build step.