Question

I am attempting to do some processing in the pixel shader on a texture. The data for the texture is coming from a memory chunk of 8 bit data. The problem I am facing is how to read the data in the shader.

Code to create the texture and ressource view:

In OnD3D11CreateDevice:

D3D11_TEXTURE2D_DESC tDesc;
tDesc.Height = 480;
tDesc.Width = 640;
tDesc.Usage = D3D11_USAGE_DYNAMIC;
tDesc.MipLevels = 1;
tDesc.ArraySize = 1;
tDesc.SampleDesc.Count = 1;
tDesc.SampleDesc.Quality = 0;
tDesc.Format = DXGI_FORMAT_R8_UINT;
tDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
tDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE;
tDesc.MiscFlags = 0;
V_RETURN(pd3dDevice->CreateTexture2D(&tDesc, NULL, &g_pCurrentImage));
D3D11_SHADER_RESOURCE_VIEW_DESC rvDesc;
g_pCurrentImage->GetDesc(&tDesc);
rvDesc.Format = DXGI_FORMAT_R8_UINT;
rvDesc.Texture2D.MipLevels = tDesc.MipLevels;
rvDesc.Texture2D.MostDetailedMip = tDesc.MipLevels - 1;
rvDesc.ViewDimension = D3D_SRV_DIMENSION_TEXTURE2D;
V_RETURN(pd3dDevice->CreateShaderResourceView(g_pCurrentImage, &rvDesc, &g_pImageRV));    </code>

in OnD3D11FrameRender:

HRESULT okay;

if( !g_updateDone ) {
    D3D11_MAPPED_SUBRESOURCE resource;
    resource.pData = mImage.GetData();
    resource.RowPitch = 640;
    resource.DepthPitch = 1;
    okay = pd3dImmediateContext->Map(g_pCurrentImage, 0, D3D11_MAP_WRITE_DISCARD, 0, &resource);

    g_updateDone = true;
}

pd3dImmediateContext->PSSetShaderResources(0, 1, &g_pImageRV);

This returns no errors so far, everything seems to work.

The HLSL Shader:

//-----  
// Textures and Samplers  
//-----  

Texture2D <int> g_txDiffuse : register( t0 );  
SamplerState g_samLinear : register( s0 );  

//-----  
// shader input/output structure  
//-----  

struct VS_INPUT  
{  
    float4 Position     : POSITION; // vertex position   
    float2 TextureUV    : TEXCOORD0;// vertex texture coords   
};  

struct VS_OUTPUT  
{  
    float4 Position     : SV_POSITION; // vertex position   
    float2 TextureUV    : TEXCOORD0;   // vertex texture coords   
};  

//-----  
// Vertex shader  
//-----  
VS_OUTPUT RenderSceneVS( VS_INPUT input )  
{  
    VS_OUTPUT Output;  

    Output.Position = input.Position;  

    Output.TextureUV = input.TextureUV;   

    return Output;      
}  

//-----  
// Pixel Shader  
//-----  

float4 RenderScenePS( VS_OUTPUT In ) : SV_TARGET  
{   
    int3 loc;  
    loc.x = 0;  
    loc.y = 0;  
    loc.z = 1;  
    int r = g_txDiffuse.Load(loc);  
    //float fTest = (float) r;  

    return float4( In.TextureUV.x, In.TextureUV.y, In.TextureUV.x + In.TextureUV.y, 1);  
}

The thing is, I can’t even debug it in PIX to see what r results in, because even with Shader optimization disabled, the line int r = … is never reached

I tested

float fTest = (float) r;
return float4( In.TextureUV.x, In.TextureUV.y, In.TextureUV.x + In.TextureUV.y, fTest);

but this would result in “cannot map expression to pixel shader instruction set”, even though it’s a float.

So how do I read and use 8bit integers from a texture, and if possible, with no sampling at all.

Thanks for any feedback.

Answer 1

Oh my this is a really old question, I thought it said 2012!

But anyway as it’s still open:

Due to the nature of GPU’s being optimised for floating point arithmetic, you probably wont get a great deal of performance advantage by using a Texture2D<int> over a Texture2D<float>.

You could attempt to use a Texture2D<float> and then try:

return float4( In.TextureUV.x, In.TextureUV.y, In.TextureUV.x + In.TextureUV.y, g_txDiffuse.Load(loc));