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?

Answer 1

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.