uniform sampler2D shadow2DTex;
uniform sampler2DShadow shadowMap;

/* Part of this PCSS is from http://developer.download.nvidia.com/whitepapers/2008/PCSS_Integration.pdf */
#if SMALL_SHADOW
#define BLOCKER_SEARCH_NUM_SAMPLES 16
#define PCF_NUM_SAMPLES 16
#else
#define BLOCKER_SEARCH_NUM_SAMPLES 64
#define PCF_NUM_SAMPLES 64
#endif
#define LIGHT_SIZE_UV (0.1)

vec2 poissonDisk[64];

float FindBlocker(out float numBlockers, vec3 coord)
{
	float searchWidth = 0.025;
	float blockerSum = 0;
	numBlockers = 0;
	for( int i = 0; i < BLOCKER_SEARCH_NUM_SAMPLES; i++ ) {
#ifdef GL_ES
		float shadowMapDepth = texture2D(shadow2DTex, coord.xy + poissonDisk[i] * searchWidth).r;
#else
        float shadowMapDepth = texture(shadow2DTex, coord.xy + poissonDisk[i] * searchWidth).r;
#endif
		if ( shadowMapDepth < coord.z ) {
			blockerSum += coord.z - shadowMapDepth;
			numBlockers++;
		}
	}
	return blockerSum / numBlockers;
}

float PCF_Filter(vec4 coord, float filterRadiusUV)
{
	float sum = 0.0f;
	for ( int i = 0; i < PCF_NUM_SAMPLES; i++ ) {
		vec4 offset = vec4(poissonDisk[i] * filterRadiusUV, 0.0, 0.0);
		sum += shadow2DProj(shadowMap, coord + offset).r;
	}
	return sum / PCF_NUM_SAMPLES;
}

float PCSS (vec4 coord)
{
#if SMALL_SHADOW
	poissonDisk[0] = vec2( -0.94201624, -0.39906216 );
	poissonDisk[1] = vec2( 0.94558609, -0.76890725 );
	poissonDisk[2] = vec2( -0.094184101, -0.92938870 );
	poissonDisk[3] = vec2( 0.34495938, 0.29387760 );
	poissonDisk[4] = vec2( -0.91588581, 0.45771432 );
	poissonDisk[5] = vec2( -0.81544232, -0.87912464 );
	poissonDisk[6] = vec2( -0.38277543, 0.27676845 );
	poissonDisk[7] = vec2( 0.97484398, 0.75648379 );
	poissonDisk[8] = vec2( 0.44323325, -0.97511554 );
	poissonDisk[9] = vec2( 0.53742981, -0.47373420 );
	poissonDisk[10] = vec2( -0.26496911, -0.41893023 );
	poissonDisk[11] = vec2( 0.79197514, 0.19090188 );
	poissonDisk[12] = vec2( -0.24188840, 0.99706507 );
	poissonDisk[13] = vec2( -0.81409955, 0.91437590 );
	poissonDisk[14] = vec2( 0.19984126, 0.78641367 );
	poissonDisk[15] = vec2( 0.14383161, -0.14100790 );
#else
	poissonDisk[0] = vec2(-0.613392, 0.617481);
	poissonDisk[1] = vec2(0.170019, -0.040254);
	poissonDisk[2] = vec2(-0.299417, 0.791925);
	poissonDisk[3] = vec2(0.645680, 0.493210);
	poissonDisk[4] = vec2(-0.651784, 0.717887);
	poissonDisk[5] = vec2(0.421003, 0.027070);
	poissonDisk[6] = vec2(-0.817194, -0.271096);
	poissonDisk[7] = vec2(-0.705374, -0.668203);
	poissonDisk[8] = vec2(0.977050, -0.108615);
	poissonDisk[9] = vec2(0.063326, 0.142369);
	poissonDisk[10] = vec2(0.203528, 0.214331);
	poissonDisk[11] = vec2(-0.667531, 0.326090);
	poissonDisk[12] = vec2(-0.098422, -0.295755);
	poissonDisk[13] = vec2(-0.885922, 0.215369);
	poissonDisk[14] = vec2(0.566637, 0.605213);
	poissonDisk[15] = vec2(0.039766, -0.396100);
	poissonDisk[16] = vec2(0.751946, 0.453352);
	poissonDisk[17] = vec2(0.078707, -0.715323);
	poissonDisk[18] = vec2(-0.075838, -0.529344);
	poissonDisk[19] = vec2(0.724479, -0.580798);
	poissonDisk[20] = vec2(0.222999, -0.215125);
	poissonDisk[21] = vec2(-0.467574, -0.405438);
	poissonDisk[22] = vec2(-0.248268, -0.814753);
	poissonDisk[23] = vec2(0.354411, -0.887570);
	poissonDisk[24] = vec2(0.175817, 0.382366);
	poissonDisk[25] = vec2(0.487472, -0.063082);
	poissonDisk[26] = vec2(-0.084078, 0.898312);
	poissonDisk[27] = vec2(0.488876, -0.783441);
	poissonDisk[28] = vec2(0.470016, 0.217933);
	poissonDisk[29] = vec2(-0.696890, -0.549791);
	poissonDisk[30] = vec2(-0.149693, 0.605762);
	poissonDisk[31] = vec2(0.034211, 0.979980);
	poissonDisk[32] = vec2(0.503098, -0.308878);
	poissonDisk[33] = vec2(-0.016205, -0.872921);
	poissonDisk[34] = vec2(0.385784, -0.393902);
	poissonDisk[35] = vec2(-0.146886, -0.859249);
	poissonDisk[36] = vec2(0.643361, 0.164098);
	poissonDisk[37] = vec2(0.634388, -0.049471);
	poissonDisk[38] = vec2(-0.688894, 0.007843);
	poissonDisk[39] = vec2(0.464034, -0.188818);
	poissonDisk[40] = vec2(-0.440840, 0.137486);
	poissonDisk[41] = vec2(0.364483, 0.511704);
	poissonDisk[42] = vec2(0.034028, 0.325968);
	poissonDisk[43] = vec2(0.099094, -0.308023);
	poissonDisk[44] = vec2(0.693960, -0.366253);
	poissonDisk[45] = vec2(0.678884, -0.204688);
	poissonDisk[46] = vec2(0.001801, 0.780328);
	poissonDisk[47] = vec2(0.145177, -0.898984);
	poissonDisk[48] = vec2(0.062655, -0.611866);
	poissonDisk[49] = vec2(0.315226, -0.604297);
	poissonDisk[50] = vec2(-0.780145, 0.486251);
	poissonDisk[51] = vec2(-0.371868, 0.882138);
	poissonDisk[52] = vec2(0.200476, 0.494430);
	poissonDisk[53] = vec2(-0.494552, -0.711051);
	poissonDisk[54] = vec2(0.612476, 0.705252);
	poissonDisk[55] = vec2(-0.578845, -0.768792);
	poissonDisk[56] = vec2(-0.772454, -0.090976);
	poissonDisk[57] = vec2(0.504440, 0.372295);
	poissonDisk[58] = vec2(0.155736, 0.065157);
	poissonDisk[59] = vec2(0.391522, 0.849605);
	poissonDisk[60] = vec2(-0.620106, -0.328104);
	poissonDisk[61] = vec2(0.789239, -0.419965);
	poissonDisk[62] = vec2(-0.545396, 0.538133);
	poissonDisk[63] = vec2(-0.178564, -0.596057);
#endif

	float zReceiver = coord.z;

	float numBlockers = 0;
	float avgBlockerDepth = FindBlocker(numBlockers, coord.xyz);
	if(numBlockers < 1)
		return 1.0f;

	float filterRadiusUV = avgBlockerDepth * 0.25;
	return PCF_Filter(coord, filterRadiusUV);
}