// MinecraftPT — SH_Tracing_CS
// Low-order spherical-harmonics sky tracing: evaluates sky radiance on a small
// SH basis and stores it for ambient light estimation (used by IRC seeding).

#include "/Lib/Settings.glsl"
#include "/Lib/Utilities.glsl"
#include "/Lib/BasicFunctions/LightingConstants.glsl"
#include "/Lib/BasicFunctions/PrecomputedAtmosphere.glsl"
#include "/Lib/PathTracing/Tracer/ShadowTracing.glsl"
#include "/Lib/PathTracing/Voxelizer/VoxelProfile.glsl"

#ifdef PT_IRC


const ivec3 workGroups = ivec3(int(ceil(float(ircResolution) / 4.0)));
layout (local_size_x = 4, local_size_y = 4, local_size_z = 4) in;

layout (rgba16f) uniform writeonly image3D img_irradianceCache3D;
layout (rgba16f) uniform readonly image3D img_irradianceCache3D_Alt;

uniform sampler3D voxelData3D;

// SH basis Y1 (linear, 3 components) coefficients for sky radiance at a cell
void main(){
	ivec3 texel = ivec3(gl_GlobalInvocationID.xyz);

	if (any(greaterThanEqual(texel, ivec3(ircResolution)))){
		return;
	}

	vec3 cellPos = (vec3(texel) + 0.5) / float(ircResolution);
	vec3 worldPos = (cellPos - 0.5) * voxelDistance + cameraPosition;

	vec3 voxelCoord = cellPos * voxelResolution;
	vec4 voxelData = texelFetch(voxelData3D, ivec3(clamp(voxelCoord, vec3(0.0), vec3(voxelResolution - 1.0))), 0);
	float voxelID = DecodeVoxelID(voxelData.z);

	if (voxelID > 1.0 && voxelID < 999.0){
		return;
	}

	// Trace N directions, accumulate SH coefficients
	vec3 sh = vec3(0.0);

	for (int i = 0; i < 6; i++){
		float phi = 6.28318 * hash1(vec3(texel) * 1.3 + float(i) * 0.7);
		float cosTheta = hash1(vec3(texel) * 0.7 + float(i) * 1.9);
		float sinTheta = sqrt(1.0 - cosTheta * cosTheta);

		vec3 dir = vec3(cos(phi) * sinTheta, cosTheta, sin(phi) * sinTheta);

		float visibility = SimpleShadowTracing(WorldToVoxel(worldPos) + dir * 0.5, dir);

		vec3 radiance = GetSkyRadiance(dir, GetSunDirWorld());

		sh += radiance * visibility * cosTheta; // cos-weighted
	}

	sh /= 6.0;

	imageStore(img_irradianceCache3D, texel, vec4(sh, 1.0));
}

#endif