#include "/Lib/BasicFunctions/LightingConstants.glsl"
// MinecraftPT — SampleIRC
// Sampling the irradiance cache: a 3D grid of pre-computed diffuse irradiance
// used to cheaply evaluate indirect diffuse light.

#ifndef SAMPLE_IRC_GLSL
#define SAMPLE_IRC_GLSL

// Sample irradiance cache at a world position (trilinear)
vec3 SampleIRC(vec3 worldPos){
	vec3 voxelPos = WorldToVoxel(worldPos);

	vec3 coord = voxelPos / float(ircResolution);

	if (clamp(coord, vec3(0.0), vec3(1.0)) == coord){
		coord *= float(ircResolution) - 1.0;

		vec3 base = floor(coord);
		vec3 frac = coord - base;
		ivec3 i0 = ivec3(base);
		ivec3 i1 = min(i0 + 1, ivec3(ircResolution - 1));

		vec3 c000 = texelFetch(irradianceCache3D, i0, 0).rgb;
		vec3 c100 = texelFetch(irradianceCache3D, ivec3(i1.x, i0.y, i0.z), 0).rgb;
		vec3 c010 = texelFetch(irradianceCache3D, ivec3(i0.x, i1.y, i0.z), 0).rgb;
		vec3 c110 = texelFetch(irradianceCache3D, ivec3(i1.x, i1.y, i0.z), 0).rgb;
		vec3 c001 = texelFetch(irradianceCache3D, ivec3(i0.x, i0.y, i1.z), 0).rgb;
		vec3 c101 = texelFetch(irradianceCache3D, ivec3(i1.x, i0.y, i1.z), 0).rgb;
		vec3 c011 = texelFetch(irradianceCache3D, ivec3(i0.x, i1.y, i1.z), 0).rgb;
		vec3 c111 = texelFetch(irradianceCache3D, i1, 0).rgb;

		vec3 x00 = mix(c000, c100, frac.x);
		vec3 x10 = mix(c010, c110, frac.x);
		vec3 x01 = mix(c001, c101, frac.x);
		vec3 x11 = mix(c011, c111, frac.x);
		vec3 y0 = mix(x00, x10, frac.y);
		vec3 y1 = mix(x01, x11, frac.y);

		return mix(y0, y1, frac.z);
	}

	// Outside the cache — fall back to sky ambient
	return GetCelestialIrradiance() + GetAtmoIrradiance();
}

// Normal-aware IRC sampling (bias by surface normal facing)
vec3 SampleIRCNormal(vec3 worldPos, vec3 normal){
	vec3 irc = SampleIRC(worldPos);
	// Simple hemisphere shading via normal alignment with up
	float upFactor = normal.y * 0.5 + 0.5;
	return irc * (0.5 + 0.5 * upFactor);
}

#endif