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Fix: Cycles Light Tree gives low weight to distant lights in large volume

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The original paper only considers the minimal distance of the cluster to
the ray, not the interval length, resulting in low weight for distant
lights that have large influence over a long distance.
This commit modifies the measure by considering `theta_b - theta_a` for
local lights and the ray length `t` for distant lights.

Pull Request: https://projects.blender.org/blender/blender/pulls/123537
This commit is contained in:
Weizhen Huang 2024-06-24 12:48:08 +02:00 committed by Weizhen Huang
parent 1663df0c8f
commit 6fbc958e89
4 changed files with 50 additions and 18 deletions
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13
intern/cycles/kernel/light/background.h
View File

@ -437,11 +437,22 @@ ccl_device float background_light_pdf(KernelGlobals kg, float3 P, float3 directi
return pdf;
}
template<bool in_volume_segment>
ccl_device_forceinline bool background_light_tree_parameters(const float3 centroid,
const float t,
ccl_private float &cos_theta_u,
ccl_private float2 &distance,
ccl_private float3 &point_to_centroid)
ccl_private float3 &point_to_centroid,
ccl_private float &theta_d)
{
if (in_volume_segment) {
if (t == FLT_MAX) {
/* In world volume, distant light has no contribution. */
return false;
}
theta_d = t;
}
/* Cover the whole sphere */
cos_theta_u = -1.0f;

13
intern/cycles/kernel/light/distant.h
View File

@ -129,12 +129,23 @@ ccl_device bool distant_light_sample_from_intersection(KernelGlobals kg,
return true;
}
template<bool in_volume_segment>
ccl_device_forceinline bool distant_light_tree_parameters(const float3 centroid,
const float theta_e,
const float t,
ccl_private float &cos_theta_u,
ccl_private float2 &distance,
ccl_private float3 &point_to_centroid)
ccl_private float3 &point_to_centroid,
ccl_private float &theta_d)
{
if (in_volume_segment) {
if (t == FLT_MAX) {
/* In world volume, distant light has no contribution. */
return false;
}
theta_d = t;
}
/* Treating it as a disk light 1 unit away */
cos_theta_u = fast_cosf(theta_e);

40
intern/cycles/kernel/light/tree.h
View File

@ -135,6 +135,7 @@ ccl_device void light_tree_importance(const float3 N_or_D,
const float max_distance,
const float min_distance,
const float energy,
const float theta_d,
ccl_private float &max_importance,
ccl_private float &min_importance)
{
@ -213,9 +214,9 @@ ccl_device void light_tree_importance(const float3 N_or_D,
/* TODO: find a good approximation for f_a. */
const float f_a = 1.0f;
/* TODO: also consider t (or theta_a, theta_b) for volume */
max_importance = fabsf(f_a * cos_min_incidence_angle * energy * cos_min_outgoing_angle /
(in_volume_segment ? min_distance : sqr(min_distance)));
/* Use `(theta_b - theta_a) / d` for volume, see Eq. (4) in the paper. */
max_importance = fabsf(f_a * cos_min_incidence_angle * energy * cos_min_outgoing_angle *
(in_volume_segment ? theta_d / min_distance : 1.0f / sqr(min_distance)));
/* TODO: compute proper min importance for volume. */
if (in_volume_segment) {
@ -316,12 +317,13 @@ ccl_device void light_tree_node_importance(KernelGlobals kg,
const BoundingBox bbox = knode->bbox;
float3 point_to_centroid;
float cos_theta_u;
float distance;
float cos_theta_u, distance, theta_d;
if (knode->type == LIGHT_TREE_DISTANT) {
point_to_centroid = -bcone.axis;
cos_theta_u = fast_cosf(bcone.theta_o + bcone.theta_e);
distance = 1.0f;
/* For distant lights, the integral in Eq. (4) gives the ray length. */
theta_d = t;
if (t == FLT_MAX) {
/* In world volume, distant light has no contribution. */
return;
@ -332,10 +334,13 @@ ccl_device void light_tree_node_importance(KernelGlobals kg,
if (in_volume_segment) {
const float3 D = N_or_D;
const float closest_t = clamp(dot(centroid - P, D), 0.0f, t);
const float3 closest_point = P + D * closest_t;
const float closest_t = dot(centroid - P, D);
const float3 closest_point = P + D * clamp(closest_t, 0.0f, t);
/* Minimal distance of the ray to the cluster. */
distance = len(centroid - closest_point);
distance = len(centroid - P - D * closest_t);
/* Estimate `theta_b - theta_a` using the centroid of the cluster and the complete ray
* segment in volume. */
theta_d = fast_atan2f(t - closest_t, distance) + fast_atan2f(closest_t, distance);
/* Vector that forms a minimal angle with the emitter centroid. */
point_to_centroid = -compute_v(centroid, P, D, bcone.axis, t);
cos_theta_u = light_tree_cos_bounding_box_angle(
@ -356,6 +361,7 @@ ccl_device void light_tree_node_importance(KernelGlobals kg,
point_to_centroid = normalize_len(centroid - P, &distance);
cos_theta_u = light_tree_cos_bounding_box_angle(bbox, P, point_to_centroid);
theta_d = 1.0f;
}
/* Clamp distance to half the radius of the cluster when splitting is disabled. */
distance = fmaxf(0.5f * len(centroid - bbox.max), distance);
@ -370,6 +376,7 @@ ccl_device void light_tree_node_importance(KernelGlobals kg,
distance,
distance,
knode->energy,
theta_d,
max_importance,
min_importance);
}
@ -402,7 +409,7 @@ ccl_device void light_tree_emitter_importance(KernelGlobals kg,
BoundingCone bcone;
bcone.theta_o = kemitter->theta_o;
bcone.theta_e = kemitter->theta_e;
float cos_theta_u;
float cos_theta_u, theta_d = 1.0f;
float2 distance; /* distance.x = max_distance, distance.y = min_distance */
float3 centroid, point_to_centroid, P_c = P;
@ -414,8 +421,10 @@ ccl_device void light_tree_emitter_importance(KernelGlobals kg,
if (in_volume_segment) {
const float3 D = N_or_D;
/* Closest point from ray to the emitter centroid. */
const float closest_t = clamp(dot(centroid - P, D), 0.0f, t);
P_c += D * closest_t;
const float closest_t = dot(centroid - P, D);
P_c += D * clamp(closest_t, 0.0f, t);
const float d = len(centroid - P - D * closest_t);
theta_d = fast_atan2f(t - closest_t, d) + fast_atan2f(closest_t, d);
}
/* Early out if the emitter is guaranteed to be invisible. */
@ -444,12 +453,12 @@ ccl_device void light_tree_emitter_importance(KernelGlobals kg,
klight, centroid, P_c, N_or_D, bcone.axis, cos_theta_u, distance, point_to_centroid);
break;
case LIGHT_BACKGROUND:
is_visible = background_light_tree_parameters(
centroid, cos_theta_u, distance, point_to_centroid);
is_visible = background_light_tree_parameters<in_volume_segment>(
centroid, t, cos_theta_u, distance, point_to_centroid, theta_d);
break;
case LIGHT_DISTANT:
is_visible = distant_light_tree_parameters(
centroid, bcone.theta_e, cos_theta_u, distance, point_to_centroid);
is_visible = distant_light_tree_parameters<in_volume_segment>(
centroid, bcone.theta_e, t, cos_theta_u, distance, point_to_centroid, theta_d);
if (in_volume_segment) {
centroid = P - bcone.axis;
}
@ -477,6 +486,7 @@ ccl_device void light_tree_emitter_importance(KernelGlobals kg,
distance.x,
distance.y,
energy,
theta_d,
max_importance,
min_importance);
}

2
tests/data

@ -1 +1 @@
Subproject commit b832af0dbdedd0030c730d1d44b006c43e8cb85c
Subproject commit 218087daf891d3eefd7ac2c66eb05f117f4510bd