Conditional operator in HLSL's pass

Question

According to

http://msdn.microsoft.com/en-us/library/windows/desktop/bb509610(v=vs.85).aspx

HLSL supports conditional operator (since version 2.0? I am using 4_0)

I need to set blending state before each Draw call. In FX file I'm doing this:

BlendState BlendNone { AlphaToCoverageEnable = FALSE; BlendEnable[0] = FALSE; }; BlendState BlendSrcAlphaOne { BlendEnable[0] = TRUE; SrcBlend = SRC_ALPHA; DestBlend = INV_SRC_ALPHA; BlendOp = ADD; RenderTargetWriteMask[0] = 0x0F; }; BlendState BlendSrcAlphaOneMinusSrcAlpha { BlendEnable[0] = TRUE; SrcBlend = SRC_ALPHA; DestBlend = ONE; BlendOp = ADD; RenderTargetWriteMask[0] = 0x0F; }; int g_Blend; technique10 Render { pass P0 { SetVertexShader( CompileShader( vs_4_0, VS() ) ); SetGeometryShader( CompileShader( gs_4_0, GS() ) ); SetPixelShader( CompileShader( ps_4_0, PS() ) ); SetRasterizerState(rsCullNone); SetDepthStencilState( EnableDepth, 0 ); if (g_Blend == 0) { SetBlendState( BlendNone, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } else if (g_Blend == 1) { SetBlendState( BlendSrcAlphaOne, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } else if (g_Blend == 2) { SetBlendState( BlendSrcAlphaOneMinusSrcAlpha, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } } }

This does not compile with error: error X3000: syntax error: unexpected token 'if'

If I move the whole block into a separate function like:

void setBlend() { if (g_Blend == 0) { SetBlendState( BlendNone, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } else if (g_Blend == 1) { SetBlendState( BlendSrcAlphaOne, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } else if (g_Blend == 2) { SetBlendState( BlendSrcAlphaOneMinusSrcAlpha, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } } technique10 Render { pass P0 { SetVertexShader( CompileShader( vs_4_0, VS() ) ); SetGeometryShader( CompileShader( gs_4_0, GS() ) ); SetPixelShader( CompileShader( ps_4_0, PS() ) ); SetRasterizerState(rsCullNone); SetDepthStencilState( EnableDepth, 0 ); setBlend(); } }

it doesn't compile with error: error X3000: this FX API is not available in this part your program (SetBlendState)

So, is if supported in HLSL?

iseeall · Accepted Answer · 2012-01-03 20:29:21Z

Ok, after lots of attempts and reading http://msdn.microsoft.com/en-us/library/windows/desktop/bb205052(v=vs.85).aspx#Blend

This compiles:

BlendState blendStates[3] { { AlphaToCoverageEnable = FALSE; BlendEnable[0] = FALSE; }, { BlendEnable[0] = TRUE; SrcBlend = SRC_ALPHA; DestBlend = INV_SRC_ALPHA; BlendOp = ADD; RenderTargetWriteMask[0] = 0x0F; }, { BlendEnable[0] = TRUE; SrcBlend = SRC_ALPHA; DestBlend = ONE; BlendOp = ADD; RenderTargetWriteMask[0] = 0x0F; } }; int g_Blend; technique10 Render { pass P0 { SetVertexShader( CompileShader( vs_4_0, VS() ) ); SetGeometryShader( CompileShader( gs_4_0, GS() ) ); SetPixelShader( CompileShader( ps_4_0, PS() ) ); SetRasterizerState(rsCullNone); SetDepthStencilState( EnableDepth, 0 ); SetBlendState( blendStates[g_Blend], float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF ); } }

SetBlendState is not strictly a function call and conditional operators are not allowed inside the pass {}. However it's allowed to pass array of state objects with index instead of just state objects.

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