From 7a41bd562bdb945fbb69a11ff31c1e607965a36a Mon Sep 17 00:00:00 2001
From: Sergey Yablokov <yablokovsergey1@gmail.com>
Date: Mon, 29 Jul 2024 05:24:12 +0200
Subject: [PATCH] Doublesided area lights support

---
 SceneBase.h           |  2 ++
 internal/SceneCPU.cpp | 12 +++++++-----
 internal/SceneGPU.h   |  8 +++++---
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/SceneBase.h b/SceneBase.h
index 87886cb3..f458bffd 100644
--- a/SceneBase.h
+++ b/SceneBase.h
@@ -233,6 +233,7 @@ struct spot_light_desc_t {
 struct rect_light_desc_t {
     float color[3] = {1.0f, 1.0f, 1.0f};
     float width = 1.0f, height = 1.0f;
+    bool doublesided = false;
     bool sky_portal = false;
     bool visible = true;
     bool cast_shadow = true;
@@ -245,6 +246,7 @@ struct rect_light_desc_t {
 struct disk_light_desc_t {
     float color[3] = {1.0f, 1.0f, 1.0f};
     float size_x = 1.0f, size_y = 1.0f;
+    bool doublesided = false;
     bool sky_portal = false;
     bool visible = true;
     bool cast_shadow = true;
diff --git a/internal/SceneCPU.cpp b/internal/SceneCPU.cpp
index 503d8328..bcf78b9a 100644
--- a/internal/SceneCPU.cpp
+++ b/internal/SceneCPU.cpp
@@ -655,6 +655,7 @@ Ray::LightHandle Ray::Cpu::Scene::AddLight(const rect_light_desc_t &_l, const fl
     light_t l = {};
 
     l.type = LIGHT_TYPE_RECT;
+    l.doublesided = _l.doublesided;
     l.visible = _l.visible;
     l.cast_shadow = _l.cast_shadow;
     l.sky_portal = _l.sky_portal;
@@ -689,6 +690,7 @@ Ray::LightHandle Ray::Cpu::Scene::AddLight(const disk_light_desc_t &_l, const fl
     light_t l = {};
 
     l.type = LIGHT_TYPE_DISK;
+    l.doublesided = _l.doublesided;
     l.visible = _l.visible;
     l.cast_shadow = _l.cast_shadow;
     l.sky_portal = _l.sky_portal;
@@ -813,10 +815,10 @@ Ray::MeshInstanceHandle Ray::Cpu::Scene::AddMeshInstance(const mesh_instance_des
 
                 new_lights.emplace_back();
                 light_t &new_light = new_lights.back();
-                new_light.visible = 0;
-                new_light.cast_shadow = 1;
                 new_light.type = LIGHT_TYPE_TRI;
                 new_light.doublesided = (back_emissive != 0xffff) ? 1 : 0;
+                new_light.cast_shadow = 1;
+                new_light.visible = 0;
                 new_light.sky_portal = 0;
                 new_light.ray_visibility = mi.ray_visibility;
                 new_light.ray_visibility &= ~RAY_TYPE_CAMERA_BIT;
@@ -1258,7 +1260,7 @@ void Ray::Cpu::Scene::RebuildLightTree_nolock() {
             area = l.rect.area;
 
             axis = normalize(Ray::Cpu::cross(u, v));
-            omega_n = 0.0f; // single normal
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_DISK: {
@@ -1272,7 +1274,7 @@ void Ray::Cpu::Scene::RebuildLightTree_nolock() {
             area = l.disk.area;
 
             axis = normalize(Ray::Cpu::cross(u, v));
-            omega_n = 0.0f; // single normal
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_TRI: {
@@ -1297,7 +1299,7 @@ void Ray::Cpu::Scene::RebuildLightTree_nolock() {
             area = 0.5f * length(light_forward);
 
             axis = normalize(light_forward);
-            omega_n = PI; // normals in all directions (triangle lights are double-sided)
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_ENV: {
diff --git a/internal/SceneGPU.h b/internal/SceneGPU.h
index 04e3246a..dc921c66 100644
--- a/internal/SceneGPU.h
+++ b/internal/SceneGPU.h
@@ -1257,6 +1257,7 @@ inline Ray::LightHandle Ray::NS::Scene::AddLight(const rect_light_desc_t &_l, co
     light_t l = {};
 
     l.type = LIGHT_TYPE_RECT;
+    l.doublesided = _l.doublesided;
     l.visible = _l.visible;
     l.cast_shadow = _l.cast_shadow;
     l.sky_portal = _l.sky_portal;
@@ -1291,6 +1292,7 @@ inline Ray::LightHandle Ray::NS::Scene::AddLight(const disk_light_desc_t &_l, co
     light_t l = {};
 
     l.type = LIGHT_TYPE_DISK;
+    l.doublesided = _l.doublesided;
     l.visible = _l.visible;
     l.cast_shadow = _l.cast_shadow;
     l.sky_portal = _l.sky_portal;
@@ -2276,7 +2278,7 @@ inline void Ray::NS::Scene::RebuildLightTree_nolock() {
             area = l.rect.area;
 
             axis = normalize(NS::cross(u, v));
-            omega_n = 0.0f; // single normal
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_DISK: {
@@ -2290,7 +2292,7 @@ inline void Ray::NS::Scene::RebuildLightTree_nolock() {
             area = l.disk.area;
 
             axis = normalize(NS::cross(u, v));
-            omega_n = 0.0f; // single normal
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_TRI: {
@@ -2315,7 +2317,7 @@ inline void Ray::NS::Scene::RebuildLightTree_nolock() {
             area = 0.5f * length(light_forward);
 
             axis = normalize(light_forward);
-            omega_n = PI; // normals in all directions (triangle lights are double-sided)
+            omega_n = l.doublesided ? PI : 0.0f;
             omega_e = PI / 2.0f;
         } break;
         case LIGHT_TYPE_ENV: {