Predefined shader preprocessor macros

When compiling shader programs, Unity defines several preprocessor macros.

Target platform

• SHADER_API_OPENGL - desktop OpenGL
• SHADER_API_D3D9 - Direct3D 9
• SHADER_API_XBOX360 - Xbox 360
• SHADER_API_PS3 - PlayStation 3
• SHADER_API_D3D11 - desktop Direct3D 11
• SHADER_API_GLES - OpenGL ES 2.0 (desktop or mobile), use presence of SHADER_API_MOBILE to determine.
• SHADER_API_FLASH - Flash Stage3D
• SHADER_API_D3D11_9X - Direct3D 11 target for Windows RT

Additionally, SHADER_TARGET_GLSL is defined when the target shading language is GLSL (always true when SHADER_API_GLES is defined; and can be true for SHADER_API_OPENGL when #pragma glsl is used).

SHADER_API_MOBILE is defined for SHADER_API_GLES when compiling for “mobile” platform (iOS/Android); and not defined when compiling for “desktop” (NativeClient).

Platform difference helpers

Direct use of these platform macros is discouraged, since it’s not very future proof. For example, if you’re writing a shader that checks for D3D9, then maybe in the future the check should be extended to include D3D11. Instead, Unity defines several helper macros (in HLSLSupport.cginc) to help with that.

• UNITY_ATTEN_CHANNEL - which channel of light attenuation texture contains the data; used in per-pixel lighting code. Defined to either ‘r’ or ‘a’.
• UNITY_HALF_TEXEL_OFFSET - defined on platforms that need a half-texel offset adjustment in mapping texels to pixels (e.g. Direct3D 9).
• UNITY_UV_STARTS_AT_TOP - always defined with value or 1 or 0; value of one is on platforms where texture V coordinate is zero at “top of the texture”. Direct3D-like platforms use value of 1; OpenGL-like platforms use value of 0.
• UNITY_MIGHT_NOT_HAVE_DEPTH_TEXTURE - defined if a platform might emulate shadow maps or depth textures by manually rendering depth into a texture.
• UNITY_PROJ_COORD(a) - given a 4-component vector, return a texture coordinate suitable for projected texture reads. On most platforms this returns the given value directly.
• UNITY_NEAR_CLIP_VALUE - defined to the value of near clipping plane; Direct3D-like platforms use 0.0 while OpenGL-like platforms use –1.0.
• UNITY_COMPILER_CG, UNITY_COMPILER_HLSL or UNITY_COMPILER_HLSL2GLSL determine which underlying shader compiler is used; use in case of subtle syntax differences force you to write different shader code.
• UNITY_CAN_COMPILE_TESSELLATION - defined when the shader compiler “understands” tessellation shader HLSL syntax (currently only D3D11).
• UNITY_INITIALIZE_OUTPUT(type,name) - initialize variable name of given type to zero.
• UNITY_COMPILER_HLSL, UNITY_COMPILER_HLSL2GLSL, UNITY_COMPILER_CG - indicates which shader compiler is being used to compile shaders. Respectively, Microsoft’s HLSL (used for DX11, Xbox360, WinRT), HLSL to GLSL translator (used for iOS/Android and desktop OpenGL when #pragma glsl), and NVIDIA’s Cg (used for D3D9 and non-GLSL desktop OpenGL targets). Use this if you run into very specific corner case shader syntax handling differences between the compilers, and want to write different code for each compiler.

Shadow mapping macros

Declaring and sampling shadow maps can be very different depending on the platform, so Unity has several macros to help with that:

• UNITY_DECLARE_SHADOWMAP(tex) - declares a shadowmap texture variable with name “tex”.
• UNITY_SAMPLE_SHADOW(tex,uv) - samples shadowmap texture “tex” at given “uv” coordinate (XY components are texture location, Z component is depth to compare with). Returns single float value with the shadow term in 0..1 range.
• UNITY_SAMPLE_SHADOW_PROJ(tex,uv) - similar to above, but does a projective shadowmap read. “uv” is a float4, all other components are divided by .w for doing the lookup.

Constant buffer macros

Direct3D 11 groups all shader variables into “constant buffers”. Most of Unity’s built-in variables are already grouped, but for variables in your own shaders it might be more optimal to put them into separate constant buffers depending on expected frequency of updates.

Use CBUFFER_START(name) and CBUFFER_END macros for that:

    CBUFFER_START(MyRarelyUpdatedVariables)
    float4 _SomeGlobalValue;
    CBUFFER_END

Surface shader pass indicators

When Surface Shaders are compiled, they end up generating a lot of code for various passes to do lighting. When compiling each pass, one of the following macros is defined:

• UNITY_PASS_FORWARDBASE - forward rendering base pass (main directional light, lightmaps, SH).
• UNITY_PASS_FORWARDADD - forward rendering additive pass (one light per pass).
• UNITY_PASS_PREPASSBASE - deferred lighting base pass (renders normals & specular exponent).
• UNITY_PASS_PREPASSFINAL - deferred lighting final pass (applies lighting & textures).
• UNITY_PASS_SHADOWCASTER - shadow caster rendering pass.
• UNITY_PASS_SHADOWCOLLECTOR - shadow “gathering” pass for directional light shadows.