Branching

Xpanda's preprocessor is also capable of branching:

// Simple if
#if expression
  // ..
#endif

// If with else branch
#if expression
  // ...
#else
  // ...
#endif

// Branches like these can be simplified using elif
#if expression1
  // ...
#else
  #if expression2
    // ...
  #endif
#endif

#if expression1
  // ...
#elif expression2
  // ...
#endif

// You can chain as many elifs as you want
#if expression1
  // ...
#elif expression2
  // ...
#elif expression3
  // ...
#else
  // ...
#endif

In the current implementation, expressions are evaluated using Python's eval. If an expression evaluates to true (or anything that would pass in if), then the code is included in the shader. If Python fails to eval the expression, then both the directive and the code it surrounds are left in the shader!

C-like operators/keywords &&, ||, !, true, false in expressions are automatically translated to their Python counterparts before eval. You shouldn't directly use Python's and, or, not, True, False in expressions, since their evaluation process may be a subject to change in the future!

Examples:

#if XGLSL
  // Code to include only in GLSL shaders
#else
  // Code to include only in HLSL shaders
#endif

#if XHLSL
  // Code common for both HLSL9 and HLSL11
  #if XHLSL9
    // HLSL9 specific code
  #else
    // HLSL11 specific code
  #endif
#endif

#if (X * 2 > 4) && !((A || B) && C)
  // Complex conditions like these are also supported
#endif

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