uniform PrecalcParams
{
	int n_samples;
	float roughness;
};

uniform samplerCube environment_map;

vec2 hammersley(int i, int count)
{
	float y = bitfieldReverse(uint(i))*2.3283064e-10;
	return vec2(float(i)/count, y);
}

vec3 uv_to_hemisphere(float u, float v)
{
	float phi = u*2.0*PI;
	float r = sqrt(1.0-v*v);
	return vec3(cos(phi)*r, sin(phi)*r, v);
}

vec3 ndist_ggxtr_importance_sample(vec2 uv, float roughness)
{
	float rough_q = roughness*roughness;
	rough_q *= rough_q;
	float v = sqrt((1.0-uv.y)/(1.0+(rough_q-1.0)*uv.y));
	return uv_to_hemisphere(uv.x, v);
}