source: downloads/Samples/Media/materials/programs/DepthShadowmapReceiverFp.glsl @ 3

uniform float inverseShadowmapSize;
uniform float fixedDepthBias;
uniform float gradientClamp;
uniform float gradientScaleBias;
uniform float shadowFuzzyWidth;

uniform sampler2D shadowMap;

void main()
{
        vec4 shadowUV = gl_TexCoord[0];
        // point on shadowmap
#if LINEAR_RANGE
        shadowUV.xy = shadowUV.xy / shadowUV.w;
#else
        shadowUV = shadowUV / shadowUV.w;
#endif
        float centerdepth = texture2D(shadowMap, shadowUV.xy).x;
    
    // gradient calculation
        float pixeloffset = inverseShadowmapSize;
    vec4 depths = vec4(
        texture2D(shadowMap, shadowUV.xy + vec2(-pixeloffset, 0)).x,
        texture2D(shadowMap, shadowUV.xy + vec2(+pixeloffset, 0)).x,
        texture2D(shadowMap, shadowUV.xy + vec2(0, -pixeloffset)).x,
        texture2D(shadowMap, shadowUV.xy + vec2(0, +pixeloffset)).x);

        vec2 differences = abs( depths.yw - depths.xz );
        float gradient = min(gradientClamp, max(differences.x, differences.y));
        float gradientFactor = gradient * gradientScaleBias;

        // visibility function
        float depthAdjust = gradientFactor + (fixedDepthBias * centerdepth);
        float finalCenterDepth = centerdepth + depthAdjust;

        // shadowUV.z contains lightspace position of current object

#if FUZZY_TEST
        // fuzzy test - introduces some ghosting in result and doesn't appear to be needed?
        //float visibility = saturate(1 + delta_z / (gradient * shadowFuzzyWidth));
        float visibility = saturate(1 + (finalCenterDepth - shadowUV.z) * shadowFuzzyWidth * shadowUV.w);

        gl_FragColor = vertexColour * visibility;
#else
        // hard test
#if PCF
        // use depths from prev, calculate diff
        depths += depthAdjust;
        float final = (finalCenterDepth > shadowUV.z) ? 1.0 : 0.0;
        final += (depths.x > shadowUV.z) ? 1.0 : 0.0;
        final += (depths.y > shadowUV.z) ? 1.0 : 0.0;
        final += (depths.z > shadowUV.z) ? 1.0 : 0.0;
        final += (depths.w > shadowUV.z) ? 1.0 : 0.0;
        
        final *= 0.2;

        gl_FragColor = vec4(gl_Color.xyz * final, 1);
        
#else
        gl_FragColor = (finalCenterDepth > shadowUV.z) ? gl_Color : vec4(0,0,0,1);
#endif

#endif
   
}