#define M_PI 3.14159265359

layout(push_constant, std430) uniform Params {
	uint sample_count;
	float roughness;
	uint source_size;
	uint dest_size;

	vec2 border_size;
	bool use_direct_write;
	uint pad;
}
params;

vec3 ImportanceSampleGGX(vec2 xi, float roughness4) {
	// Compute distribution direction
	float Phi = 2.0 * M_PI * xi.x;
	float CosTheta = sqrt((1.0 - xi.y) / (1.0 + (roughness4 - 1.0) * xi.y));
	float SinTheta = sqrt(1.0 - CosTheta * CosTheta);

	// Convert to spherical direction
	vec3 H;
	H.x = SinTheta * cos(Phi);
	H.y = SinTheta * sin(Phi);
	H.z = CosTheta;

	return H;
}

float DistributionGGX(float NdotH, float roughness4) {
	float NdotH2 = NdotH * NdotH;
	float denom = (NdotH2 * (roughness4 - 1.0) + 1.0);
	denom = M_PI * denom * denom;

	return roughness4 / denom;
}

float radicalInverse_VdC(uint bits) {
	bits = (bits << 16u) | (bits >> 16u);
	bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
	bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
	bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
	bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
	return float(bits) * 2.3283064365386963e-10; // / 0x100000000
}

vec2 Hammersley(uint i, uint N) {
	return vec2(float(i) / float(N), radicalInverse_VdC(i));
}