I've manage to get good results, but the way I've done is weird.
I remembered that most smoothing filters require an weight factor based on the distance of each sample to the center of the filter kernel. Intuitively, distant samples should have less impact on the shadow than closer samples. I've added that weight factor but I still got wrong results.
I turns out that it only works if I use the inverted weight function, where distant samples have more impact on the shadow result than closer ones! But does that make sense?
Here is the code. Since each sampling vectors has a length between 0 and 1, I use it to weight the sample. The final result is then renormalized to account for the weighting:
#define MAX_SAMPLES 64uniform vec2 samplingVectors[MAX_SAMPLES];uniform int numSamples;uniform sampler2D noiseTexture;float sampleSoftShadowMap(sampler2D shadowMap, vec4 shadowTexCoord, float kernelRadius= 0.007){ float result= 0.0; float kernelRotationAngle= texture2D(noiseTexture, gl_TexCoord[0].st*vec2(42.5, 32.8)*2.0).x*2.0*3.14; mat2 kernelRotationMatrix= mat2(cos(kernelRotationAngle), -sin(kernelRotationAngle), sin(kernelRotationAngle), cos(kernelRotationAngle)); vec2 texcoord= shadowTexCoord.xy/shadowTexCoord.w*0.5+ 0.5; float sum= 0.0f; for(int i= 0; i< numSamples; ++i){ float occluderDepth= texture2D(shadowMap, texcoord+ samplingVectors*kernelRotationMatrix*kernelRadius*5.0).x; if(shadowTexCoord.z< occluderDepth+ 0.005) result+= length(samplingVectors); sum+= length(samplingVectors); } return result/sum;
As you can see, the shadow is a bit jittered but the transition is not soft. In fact, the aliased shadow is still visible in the middle of the jittered effect.
For the jittering I'm using a disk of 16 sampling positions that are passed to the shader as constants and are "randomly" rotated per-pixel. The random rotation is performed by reading a texture that contains a different rotation angle per pixel which is used to generate a 2D rotation matrix that is applied to all the sampling positions (not the most efficient solution, I know).
The shadowmap sampling and depth comparison is done manually since I'm using linear depth shadowmaps.
Here is the code. Can someone tell me what is the problem?
