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EEVEE: Volumetrics: Add Area light shape support 

Previously area lights were just considered as point lights.
We now use a "most representative point" technique that make the
light shape appearant and gives more homogenous result.

This technique is quite cheap but it is not physically correct.

So I came up with a power function to have almost the same intensity
output as cycles in the general case.
This commit is contained in:
Clément Foucault 2021-03-19 17:28:37 +01:00
parent 0a0f737f91
commit 355f884b2f
2 changed files with 29 additions and 4 deletions
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16
source/blender/draw/engines/eevee/eevee_lights.c
View File

@ -72,7 +72,7 @@ static void light_shape_parameters_set(EEVEE_Light *evli, const Light *la, const
evli->sizey = max_ff(0.003f, la->area_size * scale[1] * 0.5f);
}
/* For volume point lighting. */
evli->radius = max_ff(0.001f, hypotf(evli->sizex, evli->sizey));
evli->radius = max_ff(0.001f, hypotf(evli->sizex, evli->sizey) * 0.5f);
}
else if (la->type == LA_SUN) {
evli->radius = max_ff(0.001f, tanf(min_ff(la->sun_angle, DEG2RADF(179.9f)) / 2.0f));
@ -111,14 +111,22 @@ static float light_shape_power_get(const Light *la, const EEVEE_Light *evli)
return power;
}
static float light_shape_power_volume_get(const Light *la, float area_power)
static float light_shape_power_volume_get(const Light *la,
const EEVEE_Light *evli,
float area_power)
{
/* Volume light is evaluated as point lights. Remove the shape power. */
float power = 1.0f / area_power;
/* Make illumination power constant */
if (la->type == LA_AREA) {
/* Match cycles. Empirical fit... must correspond to some constant. */
power *= 0.0792f * M_PI;
/* This corrects for area light most representative point trick. The fit was found by
* reducing the average error compared to cycles. */
float area = evli->sizex * evli->sizey;
float tmp = M_PI_2 / (M_PI_2 + sqrtf(area));
/* Lerp between 1.0 and the limit (1 / pi). */
power *= tmp + (1.0f - tmp) * M_1_PI;
}
else if (ELEM(la->type, LA_SPOT, LA_LOCAL)) {
/* Match cycles. Empirical fit... must correspond to some constant. */
@ -191,7 +199,7 @@ static void eevee_light_setup(Object *ob, EEVEE_Light *evli)
float shape_power = light_shape_power_get(la, evli);
mul_v3_fl(evli->color, shape_power * la->energy);
evli->volume *= light_shape_power_volume_get(la, shape_power);
evli->volume *= light_shape_power_volume_get(la, evli, shape_power);
/* No shadow by default */
evli->shadow_id = -1.0f;

17
source/blender/draw/engines/eevee/shaders/volumetric_lib.glsl
View File

@ -90,6 +90,23 @@ vec3 light_volume_light_vector(LightData ld, vec3 P)
if (ld.l_type == SUN) {
return -ld.l_forward;
}
else if (ld.l_type == AREA_RECT || ld.l_type == AREA_ELLIPSE) {
vec3 L = P - ld.l_position;
vec2 closest_point = vec2(dot(ld.l_right, L), dot(ld.l_up, L));
vec2 max_pos = vec2(ld.l_sizex, ld.l_sizey);
closest_point /= max_pos;
if (ld.l_type == AREA_ELLIPSE) {
closest_point /= max(1.0, length(closest_point));
}
else {
closest_point = clamp(closest_point, -1.0, 1.0);
}
closest_point *= max_pos;
vec3 L_prime = ld.l_right * closest_point.x + ld.l_up * closest_point.y;
return L_prime - L;
}
else {
return ld.l_position - P;
}