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Stream Out Syntax

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A geometry shader with stream out is declared with a particular syntax. This topic describes the syntax. In the effect runtime, this syntax will be converted to a call to ID3D11Device::CreateGeometryShaderWithStreamOutput.

Construct Syntax

[ StreamingShaderVar = ] ConstructGSWithSO( ShaderVar, "OutputDecl0" )
Name Description
StreamingShaderVar Optional. An ASCI string that uniquely identifies the name of a geometry shader variable with stream out. This is optional because ConstructGSWithSO can be placed directly in a SetGeometryShader or BindInterfaces call.
ShaderVar A geometry shader or vertex shader variable.
OutputDecl0 A string defining which shader outputs in stream 0 are streamed out. See below for syntax.

 

This is the syntax was defined in fx_4_0 files. Note that in gs_4_0 and vs_x shaders, there is only one stream of data. The resulting shader will output one stream to both the stream out unit and the rasterizer unit.

[ StreamingShaderVar = ] ConstructGSWithSO( ShaderVar, "OutputDecl0", "OutputDecl1", "OutputDecl2", 
"OutputDecl3", RasterizedStream )
Name Description
StreamingShaderVar Optional. An ASCI string that uniquely identifies the name of a geometry shader variable with stream out. This is optional because ConstructGSWithSO can be placed directly in a SetGeometryShader or BindInterfaces call.
ShaderVar A geometry shader or vertex shader variable.
OutputDecl0 A string defining which shader outputs in stream 0 are streamed out. See below for syntax.
OutputDecl1 A string defining which shader outputs in stream 1 are streamed out. See below for syntax.
OutputDecl2 A string defining which shader outputs in stream 2 are streamed out. See below for syntax.
OutputDecl3 A string defining which shader outputs in stream 3 are streamed out. See below for syntax.
RasterizedStream An integer specifying which stream will be sent to the rasterizer.

 

Note that gs_5_0 shaders can define up to four streams of data. The resulting shader will output one stream to the stream out unit for each non-NULL output declaration and one stream the rasterizer unit.

Stream Out Declaration Syntax

" [ Buffer: ] Semantic[ SemanticIndex ] [ .Mask ]; [ ... ; ] ... [ ... ;]"
Name Description
Buffer Optional. An integer, 0 <= Buffer < 4, specifying which stream out buffer the value will go to.
Semantic A string, along with SemanticIndex, specifying which value to output.
SemanticIndex Optional. The index associated with Semantic.
Mask Optional. A component mask, indicating which components of the value to output.

 

There is one special Semantic, labeled "$SKIP" which indicates an empty semantic, leaving the corresponding memory in the stream out buffer untouched. The $SKIP semantic cannot have a SemanticIndex, but can have a Mask.

The entire stream out declaration can be NULL.

Example

struct GSOutput
{
int4 Pos : Position;
int4 Color : Color;
int4 Texcoord : Texcoord;
};

[maxvertexcount(1)]
void gsBase (inout PointStream<GSOutput> OutputStream, inout PointStream<GSOutput> OutputStream1)
{
GSOutput output;
output.Pos = int4(1,2,3,4);
output.Color = int4(5,6,7,8);
output.Texcoord = int4(9,10,11,12);
OutputStream.Append(output);

output.Pos = int4(1,2,3,4);
    output.Color = int4(5,6,7,8);
output.Texcoord = int4(9,10,11,12);
OutputStream1.Append(output);
};


GeometryShader pGSComp = CompileShader(gs_5_0, gsBase());
GeometryShader pGSwSO = ConstructGSWithSO(pGSComp, "0:Position.xy; 1:Position.zw; 2:Color.xy", 
                                                   "3:Texcoord.xyzw; 3:$SKIP.x;", NULL, NULL, 1);

// The following two passes perform the same operation
technique11 SOPoints
{
    pass 
    {
        SetGeometryShader(ConstructGSWithSO(pGSComp, "0:Position.xy; 1:Position.zw; 2:Color.xy", 
                                                     "3:Texcoord.xyzw; 3:$SKIP.x;", NULL, NULL, 1));
    }
    pass 
    {
        SetGeometryShader(pGSwSO);
    }
}

Effects (Direct3D 11)