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Code Issues 150 Wiki Activity

Spread the light of a lamp in the fog over the size of a cell next to the lamp

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Hirek
2026-10-17 00:27:28 +02:00
parent e31a49f917
commit f1c12ca651
1 changed files with 13 additions and 6 deletions
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19
shaders/fog_inject.comp
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@@ -144,9 +144,11 @@ vec3 lamp_light(light_s light, vec3 position)
// of a cell (start, unit direction, length; view space). point samples of a lamp next to the ray change many times over with // of a cell (start, unit direction, length; view space). point samples of a lamp next to the ray change many times over with
// where in the cell they fall (the light falls off with the square of the distance), so the falloff of a lamp is integrated // where in the cell they fall (the light falls off with the square of the distance), so the falloff of a lamp is integrated
// along the segment and only the rest of its light (the cone, the edge of its reach, the phase) is sampled, at two points the // along the segment and only the rest of its light (the cone, the edge of its reach, the phase) is sampled, at two points the
// integral spreads by itself (equi-angular sampling, Kulla & Fajardo 2012). the distance of the lamp from the ray is kept to // integral spreads by itself (equi-angular sampling, Kulla & Fajardo 2012). next to the lamp the light is spread over the size
// at least half the width of the cell there: the light of a lamp seen within a cell is spread over the cell. Part: where // of a cell: the distance of the lamp from the ray grows by the width of the cell there, and the cone of a spot light starts
// between the two halves of the segment the points are (0-1) // that far behind the lamp. the point sampled moves within the cell from frame to frame, and the ray of the cell would pass at
// almost no distance from the lamp in one frame and a cell away in the next, above the tip of the cone and below it. Part:
// where between the two halves of the segment the points are (0-1)
vec3 lamp_scattering(light_s lamp, vec3 start, vec3 direction, float span, float cellwidth, float part) vec3 lamp_scattering(light_s lamp, vec3 start, vec3 direction, float span, float cellwidth, float part)
{ {
vec3 sum = vec3(0.0); vec3 sum = vec3(0.0);
@@ -162,15 +164,20 @@ vec3 lamp_scattering(light_s lamp, vec3 start, vec3 direction, float span, float
} }
float closest = dot(lamp.pos - start, direction); float closest = dot(lamp.pos - start, direction);
vec3 nearest = start + direction * closest; vec3 nearest = start + direction * closest;
float reach = max(length(lamp.pos - nearest), max(0.5 * cellwidth * max(-nearest.z, 0.0), 1e-3)); float width = max(cellwidth * max(-nearest.z, 0.0), 1e-3);
float reach = sqrt(dot(lamp.pos - nearest, lamp.pos - nearest) + width * width);
light_s cone = lamp;
if (lamp.type == LIGHT_SPOT)
cone.pos -= normalize(lamp.dir) * width;
float first = atan(-closest, reach); float first = atan(-closest, reach);
float last = atan(span - closest, reach); float last = atan(span - closest, reach);
for (int i = 0; i < 2; i++) for (int i = 0; i < 2; i++)
{ {
vec3 position = start + direction * (closest + reach * tan(mix(first, last, (float(i) + part) * 0.5))); vec3 position = start + direction * (closest + reach * tan(mix(first, last, (float(i) + part) * 0.5)));
vec3 tolight = lamp.pos - position; vec3 tolight = cone.pos - position;
// the light without its falloff, which the integral holds // the light without its falloff, which the integral holds
sum += lamp_light(lamp, position) * max(dot(tolight, tolight), 0.01) * henyey_greenstein(dot(normalize(-tolight), -direction), 0.4); vec3 fromlamp = position - lamp.pos;
sum += lamp_light(cone, position) * max(dot(tolight, tolight), 0.01) * henyey_greenstein(dot(fromlamp, -direction) * inversesqrt(max(dot(fromlamp, fromlamp), 1e-8)), 0.4);
} }
return sum * (0.5 * (last - first) / (reach * max(span, 1e-4))); return sum * (0.5 * (last - first) / (reach * max(span, 1e-4)));
} }