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Code Issues 157 Wiki Activity

Give the volumetric clouds lumps, sky and ground light and a fog colour by the angle from the sun

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Hirek
2026-10-16 22:25:11 +02:00
parent 2be85410ce
commit 8b929fc1da
5 changed files with 68 additions and 21 deletions
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39
shaders/clouds_march.comp
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@@ -28,6 +28,13 @@ const float PANORAMA_LOW = -0.1;
// scales of the light of the clouds against the shading of the surfaces (light_common.glsl: SUN_DIFFUSE_SCALE, AMBIENT_SCALE)
const float CLOUD_SUN_SCALE = 1.5;
const float CLOUD_AMBIENT_SCALE = 1.0;
// the ground under the clouds lights their bases back with this share of the light falling on it
const float CLOUD_GROUND_ALBEDO = 0.2;
// how fast the light of the sky fades into a cloud, per optical depth of the cloud above (or below) a point
const float CLOUD_AMBIENT_FADE = 0.05;
// how dense a cloud has to be to scatter the sunlight back at full: the thin edges and wisps of the side lit by the sun, seen with the
// sun behind, are darker than its bulk (the "powder" effect: the light takes a few scatterings to turn back towards the view)
const float CLOUD_POWDER = 6.0;
float henyey_greenstein(float cosangle, float g)
{
@@ -41,9 +48,18 @@ float cloud_phase(float cosangle, float scale)
return mix(henyey_greenstein(cosangle, 0.8 * scale), henyey_greenstein(cosangle, -0.25 * scale), 0.3);
}
// the light of the sky a face looking straight up (Up 1) or down (-1) gets: the uniform ambient light and the directional part of
// the sky light (sky_ssbo, light_common.glsl: sky_ambient_directional) along the vertical. with the physical atmosphere it is bluer
// and brighter from above than from the sides, so the shaded sides of the clouds take the colour of the sky above them
vec3 cloud_sky_light(float up)
{
vec3 directional = sky_ambient_sh[1].rgb * (0.488603 * up) - sky_ambient_sh[6].rgb * 0.315392 - sky_ambient_sh[8].rgb * 0.546274;
return max(weather_ambient.rgb + directional * 1.3, vec3(0.0)) * CLOUD_AMBIENT_SCALE;
}
// light of the sun reaching a point inside a layer through the cloud towards it, with the light scattered many times
// (octaves after Wrenninge), and the phase of the view
float cloud_sunlight(int index, vec3 position, float cosangle, int steps)
float cloud_sunlight(int index, vec3 position, float cosangle, int steps, float powder)
{
vec3 sun = weather_sun_direction.xyz;
cloud_layer_s layer = cloud_layers[index];
@@ -65,7 +81,7 @@ float cloud_sunlight(int index, vec3 position, float cosangle, int steps)
float spread = 1.0;
for (int octave = 0; octave < 3; octave++)
{
light += amount * exp(-depth * fade) * cloud_phase(cosangle, spread);
light += amount * exp(-depth * fade) * cloud_phase(cosangle, spread) * (octave == 0 ? powder : 1.0);
amount *= 0.5;
fade *= 0.5;
spread *= 0.5;
@@ -143,8 +159,12 @@ void main()
}
}
vec3 ambienttop = weather_ambient.rgb * CLOUD_AMBIENT_SCALE;
vec3 ambienttop = cloud_sky_light(1.0);
vec3 sunlight = weather_sun_color.rgb * CLOUD_SUN_SCALE * sunup;
// the bases are lit from below by the ground, which the sun lights through the gaps between the clouds
vec3 ambientbottom = (weather_sun_color.rgb * max(weather_sun_direction.y, 0.0) * sunup * fog_light.y + ambienttop) * CLOUD_GROUND_ALBEDO;
// seen against the sun the thin edges glow (the forward scattering); seen with the sun behind, they are dark
float powderview = clamp(1.0 - cosangle, 0.0, 1.0);
for (int k = 0; k < count && transmittance > 0.01; k++)
{
int index = order[k];
@@ -162,11 +182,14 @@ void main()
float density = cloud_layer_density(index, position, height, detail);
if (density <= 0.0)
continue;
float h = clamp((height - layer.heights.x) * layer.heights.z, 0.0, 1.0);
float sunshare = (sunup > 0.0) ? cloud_sunlight(index, position, cosangle, lightsteps) : 0.0;
// the light of the sky reaches inside through the cloud above: the base of a thick cloud is darker than its top
float above = layer.shape.y * layer.shape.x * (layer.heights.y - height);
vec3 light = sunlight * sunshare + ambienttop * mix(0.35, 1.0, h) * mix(0.25, 1.0, exp(-0.05 * above));
float powder = mix(1.0, 1.0 - exp(-density / max(layer.shape.y, 1e-6) * CLOUD_POWDER), powderview);
float sunshare = (sunup > 0.0) ? cloud_sunlight(index, position, cosangle, lightsteps, powder) : 0.0;
// the light of the sky reaches inside through the cloud above, that of the ground through the cloud below: the base of a
// thick cloud is darker than its top, and greyer, lit only by the ground and the sky at its sides
float column = layer.shape.y * layer.shape.x;
float above = column * (layer.heights.y - height);
float below = column * (height - layer.heights.x);
vec3 light = sunlight * sunshare + (ambienttop * mix(0.15, 1.0, exp(-CLOUD_AMBIENT_FADE * above)) + ambientbottom * exp(-CLOUD_AMBIENT_FADE * below)) * powder;
float through = exp(-density * step);
vec3 inscattered = light * (1.0 - through);
scattered += transmittance * inscattered;