[Bf-blender-cvs] [826086c7be2] soc-2022-many-lights-sampling: WIP: handle single- or double-sided emissive triangles differently

[Weizhen Huang]

Commit: 826086c7be2c05ad8a46209881bb81606c0e1bd0
Author: Weizhen Huang
Date:   Wed Nov 16 16:45:53 2022 +0100
Branches: soc-2022-many-lights-sampling
https://developer.blender.org/rB826086c7be2c05ad8a46209881bb81606c0e1bd0

WIP: handle single- or double-sided emissive triangles differently

===================================================================

M	intern/cycles/scene/light.cpp
M	intern/cycles/scene/light_tree.cpp
M	intern/cycles/scene/light_tree.h

===================================================================

diff --git a/intern/cycles/scene/light.cpp b/intern/cycles/scene/light.cpp
index af6623811a5..ffa5c28ea22 100644
--- a/intern/cycles/scene/light.cpp
+++ b/intern/cycles/scene/light.cpp
@@ -295,7 +295,7 @@ void LightManager::device_update_distribution(Device *device,
     if (light->is_enabled) {
       if (light_tree_enabled) {
         /* -prim_id - 1 is a light source index. */
-        LightTreePrimitive light_prim(scene, ~device_light_index, scene_light_index);
+        LightTreePrimitive light_prim(scene, ~device_light_index, scene_light_index, false);
 
         /* Distant lights get added to a separate vector. */
         if (light->light_type == LIGHT_DISTANT || light->light_type == LIGHT_BACKGROUND) {
@@ -320,6 +320,8 @@ void LightManager::device_update_distribution(Device *device,
 
   /* Similarly, we also want to keep track of the index of triangles that are emissive. */
   int object_id = 0;
+  /* TODO: add an option in the UI */
+  bool is_double_sided = true;
   foreach (Object *object, scene->objects) {
     if (progress.get_cancel())
       return;
@@ -345,7 +347,7 @@ void LightManager::device_update_distribution(Device *device,
 
       if (shader->get_use_mis() && shader->has_surface_emission) {
         if (light_tree_enabled) {
-          LightTreePrimitive light_prim(scene, i, object_id);
+          LightTreePrimitive light_prim(scene, i, object_id, is_double_sided);
           light_prims.push_back(light_prim);
         }
 
diff --git a/intern/cycles/scene/light_tree.cpp b/intern/cycles/scene/light_tree.cpp
index c9891fe6544..4838903522b 100644
--- a/intern/cycles/scene/light_tree.cpp
+++ b/intern/cycles/scene/light_tree.cpp
@@ -59,8 +59,11 @@ OrientationBounds merge(const OrientationBounds &cone_a, const OrientationBounds
   return OrientationBounds({new_axis, theta_o, theta_e});
 }
 
-LightTreePrimitive::LightTreePrimitive(Scene *scene, int prim_id, int object_id)
-    : prim_id(prim_id), object_id(object_id)
+LightTreePrimitive::LightTreePrimitive(Scene *scene,
+                                       int prim_id,
+                                       int object_id,
+                                       bool is_double_sided)
+    : prim_id(prim_id), object_id(object_id), is_double_sided(is_double_sided)
 {
   if (is_triangle()) {
     calculate_triangle_vertices(scene);
@@ -148,11 +151,16 @@ void LightTreePrimitive::calculate_bcone(Scene *scene)
   bcone = OrientationBounds::empty;
 
   if (is_triangle()) {
-    bcone.axis = safe_normalize(cross(vertices[1] - vertices[0], vertices[2] - vertices[0]));
+    if (is_double_sided) {
+      /* Any vector in the plane */
+      bcone.axis = safe_normalize(vertices[0] - vertices[1]);
+      bcone.theta_o = M_PI_2_F;
+    }
+    else {
+      bcone.axis = safe_normalize(cross(vertices[1] - vertices[0], vertices[2] - vertices[0]));
+      bcone.theta_o = 0;
+    }
 
-    /* TODO: instance emissive triangle twice in the light tree when it is double-sided. Right now,
-     * we assume that the normal axis is within pi radians of the triangle normal. */
-    bcone.theta_o = M_PI_F;
     bcone.theta_e = M_PI_2_F;
   }
   else {
diff --git a/intern/cycles/scene/light_tree.h b/intern/cycles/scene/light_tree.h
index 19d21c1872a..670590f44fc 100644
--- a/intern/cycles/scene/light_tree.h
+++ b/intern/cycles/scene/light_tree.h
@@ -63,6 +63,7 @@ struct LightTreePrimitive {
 
   /* Only used for emissive triangles */
   float3 vertices[3];
+  bool is_double_sided;
 
   float3 centroid;
   BoundBox bbox;
@@ -70,7 +71,7 @@ struct LightTreePrimitive {
   float energy;
   int prim_num;
 
-  LightTreePrimitive(Scene *scene, int prim_id, int object_id);
+  LightTreePrimitive(Scene *scene, int prim_id, int object_id, bool is_double_sided);
   void calculate_triangle_vertices(Scene *scene);
   void calculate_centroid(Scene *scene);
   void calculate_bbox(Scene *scene);