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Post Processing Texel Offsets

2 posts in this topic

Hi guys, I'm trying to do a simple horizontal blur filter. I don't understand what to use for the texture coordinate values.

This is from the DirectX PostProcess sample:


// what the hell is this ?
float2 TexelKernel[g_cKernelSize]
string ConvertPixelsToTexels = "PixelKernel";

// pixel shader part
float4 Color = 0;

for(int i=0;i<g_cKernelSize;i++){
Color += tex2D( g_samSrcColor, Tex + TexelKernel[i].xy ) * BlurWeights[i];


I am pretty sure a texel is either:


(which one ?)

...so is the TexelKernel x-values for a 5-sample filter simply:


TexelKernel[0].x= -2*texel;
TexelKernel[1].x= -1*texel;
TexelKernel[2].x= 0;
TexelKernel[3].x= 1*texel;
TexelKernel[4].x= 2*texel;



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[quote name='Endemoniada' timestamp='1329198443' post='4912903']
That one.

There is a small difference in the alignment of pixels and texels.
If you are using D3D9, you may want to look at [url="http://msdn.microsoft.com/en-us/library/windows/desktop/bb219690%28v=vs.85%29.aspx"]this[/url].
Or if you are using D3D10+ then look at [url="http://msdn.microsoft.com/en-us/library/cc308049%28VS.85%29.aspx"]this[/url].

If you use Dx10+ you can consider using the [url="http://msdn.microsoft.com/en-us/library/windows/desktop/bb509694%28v=vs.85%29.aspx"]Load[/url] intrinsic. It allows fetching data without filtering or sampling and is thus much faster if you want to access texels directly. Small sample:
[CODE]inputTexture.Load(int3(input.Position.xy, 0));[/CODE]

The position argument of the Load intrinsic is in integers, which means in [0…width-1]x[0…height-1]. The xy component of the SV_Position gives you in a pixel shader the position of the current pixel in device coordinates (with a half texel offset but that will be truncated if you cast it to int.)

Hope it helps. [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img]

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Thank you. I finally read the Directly Mapping Texels to Pixels (DIrect3D 9) article (twice) and seem to fully understand it now.

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