SDSL: unable to access custom streams after VS

vvvv gamma question
1

hi all,

I want to sample from texture array with vertex id. I can access them in VS but not in PS or GS. Do I have to pass the streams on manually each stage, or am I missing the correct shader base? I thougt streams would take care of that themselves.

Here is a stripped down version with everything stream related.
Everything works, except accessing VId and IId in PS

[Summary("")]
shader A_DrawFX : VS_PS_Base, ColorBase, ShaderUtils
{
	stream float4 PosW : POSITION1;
	stream float2 TexCd : TEXCOORD0;
	stream uint VId : SV_VertexID;
	stream uint IId : SV_InstanceID;
	
    override stage void VSMain(){ 

    	uint vid = streams.VId;  
    	uint iid = streams.IId;    	

        streams.ShadingPosition = mul(p, World);
    }

    [maxvertexcount(4)]
    void GSMain(point Input input[1], inout TriangleStream<Output> pointStream)
    {
    	streams = input[0];
        for(int i=0; i<4; i++)
        {                     
        	streams.ShadingPosition = mul(float4(quadP, 1), ViewProjection);
        	streams.TexCd.xy = QuadUV[i];
        	pointStream.Append(streams);
        }
        pointStream.RestartStrip();
    }

    override stage void PSMain(){    	
    	//uint vid = streams.VId;
    	float2 uv = streams.TexCd;
        streams.ColorTarget = glyphs.Sample(sLw, float3(uv, 0) ,0 );
    }
};
2

not sure how stride handles special semantics names like SV_VertexID which are only allowed (in HLSL) as inputs for certain stages.~~

you could definitely work around the problem, by using another stream variable to pass that data to the next stage.
so your input for VS is still ‘SV_VertexID’ but you pass it along as another stream with name ‘VertexID’

edit: didn’t read your example properly…
in case of a GS you probably need to access the data through your first input parameter (in your case point Input input[1]) and copy that to your <Output>pointStream

edit 2: you do copy input/output to stream, so first answer actually applies.
at least that’s the way i got it working in a TS/DS shader

3

Yes, that is the correct answer, SV_VertexID can only be used as input for the vertex shader. for that reason we have this shader in VL.Stride:

Just inherit from it and use

AssignVertexID();

in the vertex shader and then you can use streams.VertexID in all following stages.

4

thanks, I solved it like that.

imo it would make sense that the shader base for draw shaders would automatically include streams for vid and iid.

5

Yes, good point.