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# How to implement pcf by hand?

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3 replies to this topic

### #1five1mon  Members

Posted 07 June 2012 - 03:52 PM

Hey
I’m currently porting a shadow system from Xbox 360 to DirectX 11. As a reference we want code with the same functionality to run on DirectX. The problem is that I can’t get the bilinear pcf interpolation to work properly. I tried many variants of the code but didn’t reach a satisfying result. This is how the code stands atm:
float4 vFrac;

// Clamp the lookup coord so they will be in complete sync with the bilinear weights

// Compute the bilinear weights
vecFrac.zw = float2(1.0f, 1.0f) - vecFrac.xy;
float4 vBilinearWeights = vecFrac.zxzx * vecFrac.wwyy;

float4 vSamples;

vSamples.x = shadowMap.Sample(pointSampler, offsetCoord.xy, int2( 0.0, 0.0 )).x;
vSamples.y = shadowMap.Sample(pointSampler, offsetCoord.xy, int2( 1.0, 0.0 )).x;
vSamples.z = shadowMap.Sample(pointSampler, offsetCoord.xy, int2( 0.0, 1.0 )).x;
vSamples.w = shadowMap.Sample(pointSampler, offsetCoord.xy, int2( 1.0, 1.0 )).x;

// Compute the depth comparision for each tap

// The result
float shadow = dot(vSamples, vecBilinearWeights);
If I can get this to work I can increase the number of taps and implement other filters as well. Hardware accelerated pcf(SampleCmpLevelZero) works fine and I don’t think there’s any wrong with the texture resource.

Does anybody know how I can implement proper bilinear texture filtering on DirectX 11 without using SampleCmpLevelZero? The artefacts I experience are sharp edges where the “interpolation” seems to start sudden. As the camera moves around the penumbra flickers like the sampling was dependent on the viewing angle.

Cheers

### #2five1mon  Members

Posted 08 June 2012 - 03:18 AM

This is what it looks like

### #3MJP  Moderators

Posted 08 June 2012 - 03:02 PM

If I remember correctly, there's some 2x2 PCF code in the D3D9 ShadowMap sample included with the DX SDK.

### #4ankhd  Members

Posted 11 June 2012 - 02:22 AM

Hello.

I do mine like this.

static const float SMAP_SIZE = 2048.0f;//size of shadow texture
static const float SMAP_DX = 1.0f / SMAP_SIZE;

// Sample shadow map to get nearest depth to light.