Problems passing an XMFLOAT4 to a shader

DividedByZero · 2014-07-02T05:18:27

Hi Guys,I am trying to pass a float to a shader to control the alpha channel.The shader works fine if I hard code a value, but I am having trouble getting the float to the shader via my application.I have setup an XMFLOAT4 to a constant buffer and have set all of the values XMFLOAT4 to 0.5 (although I should only have to set the first one).But for some reason it isn't working.This is the shader (snipped a bit) cbuffer cbChangesAlpha : register(b3) { float4 image_alpha; } float4 PShader( PS_Input frag ) : SV_TARGET { float4 fRet = colorMap_.Sample( colorSampler_, frag.tex0 ); fRet.a = image_alpha.w; // works if I hard code a value return fRet; } And this is my in-app code // setting up the XMFLOAT4 constant buffer ZeroMemory(&constDesc,sizeof(constDesc)); constDesc.BindFlags=D3D11_BIND_CONSTANT_BUFFER; constDesc.ByteWidth=sizeof(XMFLOAT4); constDesc.Usage=D3D11_USAGE_DEFAULT; if(FAILED(d3dDevice->CreateBuffer(&constDesc,0,&floatCB))) return 11114; and part of my render loop XMFLOAT4 image_alpha; image_alpha.w=0.5; image_alpha.x=0.5; image_alpha.y=0.5; image_alpha.z=0.5; d3dContext->UpdateSubresource(floatCB,0,0,&image_alpha,0,0); d3dContext->VSSetConstantBuffers(3,1,&floatCB); All complies and executes ok but I just get a black screen. If I hard code the shader to be a value between 0 & 1 it works correctly. So, it seems that the image_alpha values are not getting to the shader correctly.Any advice would be awesome