// light of the sky seen by the observer in every direction, for the sky-view table (atmosphere_common.glsl), which the
// sky, the ambient light and the fog colour are read from. one invocation per texel. run every frame the sky is drawn with
// the atmosphere, after the transmittance and multiple scattering tables

#include <common>
#include <atmosphere_common.glsl>

layout(binding = ATMOSPHERE_TRANSMITTANCE_UNIT) uniform sampler2D atmo_transmittance_lut;
layout(binding = ATMOSPHERE_MULTISCATTERING_UNIT) uniform sampler2D atmo_multiscattering_lut;
#define ATMO_MULTISCATTERING_LUT
#include <atmosphere_integrate.glsl>

layout(local_size_x = 8, local_size_y = 8) in;

layout(binding = ATMOSPHERE_SKYVIEW_UNIT, rgba16f) writeonly uniform image2D skyview_target;

const int SKYVIEW_SAMPLES = 32;

void main()
{
	ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
	if (texel.x >= int(ATMOSPHERE_SKYVIEW_WIDTH) || texel.y >= int(ATMOSPHERE_SKYVIEW_HEIGHT))
		return;

	vec2 uv = (vec2(texel) + 0.5) / vec2(ATMOSPHERE_SKYVIEW_WIDTH, ATMOSPHERE_SKYVIEW_HEIGHT);
	float radius = atmo_observer_radius;
	float cosviewzenith;
	float coslightview;
	atmo_skyview_params(uv, radius, cosviewzenith, coslightview);

	float cossunzenith = clamp(atmo_sun_direction.y, -1.0, 1.0);
	vec3 sundirection = normalize(vec3(sqrt(max(1.0 - cossunzenith * cossunzenith, 0.0)), 0.0, cossunzenith));
	float sinviewzenith = sqrt(max(1.0 - cosviewzenith * cosviewzenith, 0.0));
	vec3 direction = vec3(sinviewzenith * coslightview, sinviewzenith * sqrt(max(1.0 - coslightview * coslightview, 0.0)), cosviewzenith);
	vec3 origin = vec3(0.0, 0.0, radius);

	atmo_scattering_s result = atmo_integrate(origin, direction, sundirection, false, SKYVIEW_SAMPLES, true, true);
	imageStore(skyview_target, texel, vec4(result.luminance, 1.0));
}