// the fog volume of the main view, first pass: in every cell of a grid laid over the view (slices spaced exponentially in the
// depth), how dense the fog is and how much light it scatters towards the camera. the density: the haze, the patches of the
// ground fog, the low clouds; the light: the colour the fog has towards the horizon (weather_common.glsl), less what the
// shadows of the sun and of the clouds hold back, and the lamps and headlights of the light clusters. blended with the
// previous frame, found where the cell was then; the cells are sampled at another depth every frame.
// rgb: light scattered towards the camera per metre, a: extinction per metre

#include <common>
#include <clouds_common.glsl>

layout(local_size_x = WEATHER_GROUP_SIZE, local_size_y = WEATHER_GROUP_SIZE, local_size_z = 1) in;

layout(rgba16f, binding = 0) uniform writeonly image3D fog_scattering;
layout(binding = CLOUD_HISTORY_TEX) uniform sampler3D fog_history;

#if SHADOWMAP_ENABLED
uniform sampler2DArrayShadow shadowmap;
#endif
uniform sampler2D headlightmap;
layout(binding = HEADLIGHT_SHADOW_TEX) uniform sampler2DArrayShadow headlight_shadowmap;

layout(location = 0) uniform ivec3 grid;
layout(location = 1) uniform mat4 inverse_projection;
layout(location = 2) uniform mat4 view_to_world;
// x: near, y: far, z: slices / log(far / near), w: where in its slice the cell is sampled this frame (0-1)
layout(location = 3) uniform vec4 slicing;
// world axes to the clip space of the previous frame, the camera of the previous frame at the origin
layout(location = 4) uniform mat4 previous_projection_view;
layout(location = 5) uniform vec3 previous_camera;
// x: share of this frame (1 without history), y: brightness of the lamps in the fog (0: none), z: 1 when the sun casts shadows
// into the fog, w: 1 when the headlights cast shadows into it
layout(location = 6) uniform vec4 options;
// the light of the cab lamp, which lights no fog (the air of the cab is clear), or -1
layout(location = 7) uniform int cablamp;
// x: near, y: slices / log(far / near) of the previous frame
layout(location = 8) uniform vec2 previous_slicing;

float henyey_greenstein(float cosangle, float g)
{
	float g2 = g * g;
	return (1.0 - g2) / pow(max(1.0 + g2 - 2.0 * g * cosangle, 1e-4), 1.5);
}

// share of the sunlight the shadow map holds back at a point of the view space, one comparison
float sun_shadow(vec3 position)
{
#if SHADOWMAP_ENABLED
	float span_distance = dot(position, position);
	uint cascade;
	for (cascade = 0U; cascade < MAX_CASCADES; cascade++)
		if (span_distance <= cascade_end[cascade])
			break;
	if (cascade >= MAX_CASCADES)
		return 0.0;
	vec4 lightpos = lightview[cascade] * vec4(position, 1.0);
	vec3 coords = lightpos.xyz / lightpos.w;
	if (coords.z < 0.0 || any(lessThan(coords.xy, vec2(0.0))) || any(greaterThan(coords.xy, vec2(1.0))))
		return 0.0;
	return texture(shadowmap, vec4(coords.xy, float(cascade), coords.z + 0.0001 * float(cascade + 1U)));
#else
	return 0.0;
#endif
}

// light of a lamp or of the beam of headlights at a point of the view space, before the phase
vec3 lamp_light(light_s light, vec3 position)
{
	if (light.type == LIGHT_HEADLIGHTS)
	{
		vec4 projected = light.headlight_projection * vec4(position, 1.0);
		vec3 coords = projected.xyz / projected.w;
		if (coords.z < 0.0 || coords.z > 1.0 || any(lessThan(coords.xy, vec2(0.0))) || any(greaterThan(coords.xy, vec2(1.0))))
			return vec3(0.0);
		float span_distance = length(light.pos - position);
		float atten = 1.0 / (1.0 + light.linear * span_distance + light.quadratic * span_distance * span_distance);
		atten *= mix(1.0, 0.0, clamp((coords.z - 0.998) * 500.0, 0.0, 1.0));
		vec3 beam = textureLod(headlightmap, coords.xy, 1.0).rgb * light.headlight_weights.rgb;
		float intensity = max(max(beam.r, beam.g), beam.b);
		if ((options.w > 0.5) && (light.headlight_weights.w > 0.5) && (intensity > 0.0))
		{
			// the shadow map of the beam, as in light_common.glsl without the offset along a normal
			uint map = uint(light.headlight_weights.w - 0.5);
			vec4 shadowpos = headlight_shadow[map] * vec4(position, 1.0);
			if (shadowpos.w > 0.0)
			{
				vec2 shadowcoords = shadowpos.xy / shadowpos.w;
				if (all(greaterThanEqual(shadowcoords, vec2(0.0))) && all(lessThanEqual(shadowcoords, vec2(1.0))))
				{
					float texel = headlight_shadow_params[map].x * shadowpos.w;
					float reference = shadowpos.z / max(shadowpos.w - texel * 1.5, 1e-3);
					intensity *= 1.0 - texture(headlight_shadowmap, vec4(shadowcoords, float(map), reference));
				}
			}
		}
		return light.color * (atten * intensity * light.intensity);
	}
	vec3 tolight = light.pos - position;
	float distance2 = dot(tolight, tolight);
	float edge = clamp(1.0 - distance2 * distance2 * (light.quadratic * light.quadratic), 0.0, 1.0);
	float atten = edge * edge / max(distance2, 0.01);
	if (light.type == LIGHT_SPOT)
		atten *= smoothstep(light.out_cutoff, light.in_cutoff, dot(-tolight * inversesqrt(max(distance2, 1e-8)), normalize(light.dir)));
	return light.color * (atten * light.intensity);
}

void main()
{
	ivec3 cell = ivec3(gl_GlobalInvocationID);
	if (any(greaterThanEqual(cell, grid)))
		return;
	vec2 coords = (vec2(cell.xy) + 0.5) / vec2(grid.xy);
	vec4 near = inverse_projection * vec4(coords * 2.0 - 1.0, 1.0, 1.0);
	vec3 ray = near.xyz / near.w;
	ray /= -ray.z;
	float depth = slicing.x * exp((float(cell.z) + slicing.w) / slicing.z);
	vec3 view = ray * depth;
	vec3 world = mat3(view_to_world) * view;
	float height = weather_camera.x + world.y;

	// density
	float haze = fog_haze.x * exp(-fog_haze.y * max(height, 0.0));
	float ground = fog_ground.x * exp(-fog_ground.y * max(height - fog_ground.z, 0.0));
	if (ground > 0.0 && fog_ground.w > 0.0)
	{
		float patches = textureLod(cloud_shape_noise, (world + fog_noise.xyz) * fog_noise.w, 0.0).g;
		ground *= mix(1.0, clamp((patches - 0.3) * 2.6, 0.0, 2.2), fog_ground.w);
	}
	float clouds = cloud_density_coarse(world);
	float extinction = haze + ground + clouds;

	vec4 result = vec4(0.0);
	if (extinction > 1e-7)
	{
		vec3 direction = normalize(world);
		// the light of the sky and the sun, held back by the shadows
		float sunlit = cloud_shadow(world);
		if (options.z > 0.5 && sunlit > 0.0)
			sunlit *= 1.0 - sun_shadow(view);
		vec3 light = fog_whiten(fog_color_world(direction), (ground + clouds) / extinction) * fog_light_factor(sunlit);
		// lamps and headlights of the cluster of the cell
		if (options.y > 0.0 && lights_clustered != 0U && cluster_valid != 0U)
		{
			ivec2 tile = clamp(ivec2(coords * vec2(CLUSTER_GRID_X, CLUSTER_GRID_Y)), ivec2(0), ivec2(CLUSTER_GRID_X - 1, CLUSTER_GRID_Y - 1));
			int slice = clamp(int(floor(cluster_slice_bias + log(depth) * cluster_slice_scale)), 0, CLUSTER_GRID_Z - 1);
			cluster_range_s range = cluster_ranges[uint(tile.x + CLUSTER_GRID_X * (tile.y + CLUSTER_GRID_Y * slice))];
			vec3 tocamera = -normalize(view);
			vec3 lamps = vec3(0.0);
			for (uint i = 0U; i < range.count; i++)
			{
				uint index = cluster_light_indices[range.offset + i];
				if (int(index) == cablamp)
					continue;
				light_s lamp = lights[index];
				vec3 incoming = lamp_light(lamp, view);
				if (dot(incoming, incoming) <= 0.0)
					continue;
				lamps += incoming * henyey_greenstein(dot(normalize(view - lamp.pos), tocamera), 0.4);
			}
			light += lamps * options.y;
		}
		result = vec4(light * fog_haze.w * extinction, extinction);
	}

	// the previous frame, where the cell was then
	float share = options.x;
	if (share < 1.0)
	{
		vec4 clip = previous_projection_view * vec4(world - previous_camera, 1.0);
		if (clip.w > 0.0)
		{
			vec3 previous = vec3(clip.xy / clip.w * 0.5 + 0.5, log(max(clip.w / previous_slicing.x, 1e-6)) * previous_slicing.y / float(grid.z));
			if (all(greaterThanEqual(previous, vec3(0.0))) && all(lessThanEqual(previous, vec3(1.0))))
				result = mix(textureLod(fog_history, previous, 0.0), result, share);
		}
	}
	if (any(isnan(result)))
		result = vec4(0.0);
	imageStore(fog_scattering, cell, result);
}