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How to implement pcf by hand?

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#1 five1mon   Members   


Posted 07 June 2012 - 03:52 PM

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
vecFrac.xy = modf((vShadowCoord.xy) * float2(768.0f, 768.0f), vShadowCoord.xy);
vShadowCoord.xy /= float2(768.0f, 768.0f);

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

float4 vSamples;

// Read the 4 neighbours
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
vShadowCoord.z -= 0.001f;
vSamples = step(vShadowCoord.zzzz, vSamples);

// 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.


#2 five1mon   Members   


Posted 08 June 2012 - 03:18 AM

Posted Image

This is what it looks like

#3 MJP   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.

#4 ankhd   Members   


Posted 11 June 2012 - 02:22 AM


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.
float s0 = ShadowMap.Sample(ShadowSam, projTex.xy).r;
float s1 = ShadowMap.Sample(ShadowSam, projTex.xy + float2(SMAP_DX, 0)).r;
float s2 = ShadowMap.Sample(ShadowSam, projTex.xy + float2(0, SMAP_DX)).r;
float s3 = ShadowMap.Sample(ShadowSam, projTex.xy + float2(SMAP_DX, SMAP_DX)).r;

whats casting the shadow in the image if its a raised clif then you may need to filter the vertice heights a bit to smooth them out.

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