Fix T63588: Cycles unnecessarily updates background importance sampling map

Referenced by commit 52cc412e0f, Revert "Fix T63588: Cycles unnecessarily updates background importance sampling map"
Referenced by issue #77273, Cycles crash enabling Portal for area lights
Referenced by issue #63588, Cycles does need recalculate MIP after modifying a material

intern/cycles/render/light.cpp

@@ -181,6 +181,7 @@ bool Light::has_contribution(Scene *scene)
 LightManager::LightManager()
 {
   need_update = true;
+  need_update_background = true;
   use_light_visibility = false;
 }
 
@@ -901,7 +902,7 @@ void LightManager::device_update(Device *device,
 
   VLOG(1) << "Total " << scene->lights.size() << " lights.";
 
-  device_free(device, dscene);
+  device_free(device, dscene, need_update_background);
 
   use_light_visibility = false;
 
@@ -915,9 +916,11 @@ void LightManager::device_update(Device *device,
   if (progress.get_cancel())
     return;
 
-  device_update_background(device, dscene, scene, progress);
-  if (progress.get_cancel())
-    return;
+  if (need_update_background) {
+    device_update_background(device, dscene, scene, progress);
+    if (progress.get_cancel())
+      return;
+  }
 
   device_update_ies(dscene);
   if (progress.get_cancel())
@@ -929,14 +932,17 @@ void LightManager::device_update(Device *device,
   }
 
   need_update = false;
+  need_update_background = false;
 }
 
-void LightManager::device_free(Device *, DeviceScene *dscene)
+void LightManager::device_free(Device *, DeviceScene *dscene, const bool free_background)
 {
   dscene->light_distribution.free();
   dscene->lights.free();
-  dscene->light_background_marginal_cdf.free();
-  dscene->light_background_conditional_cdf.free();
+  if (free_background) {
+    dscene->light_background_marginal_cdf.free();
+    dscene->light_background_conditional_cdf.free();
+  }
   dscene->ies_lights.free();
 }
 
@@ -989,6 +995,7 @@ int LightManager::add_ies(const string &content)
   ies_slots[slot]->hash = hash;
 
   need_update = true;
+  need_update_background = true;
 
   return slot;
 }
@@ -1007,6 +1014,7 @@ void LightManager::remove_ies(int slot)
 
   /* If the slot has no more users, update the device to remove it. */
   need_update |= (ies_slots[slot]->users == 0);
+  need_update_background |= need_update;
 }
 
 void LightManager::device_update_ies(DeviceScene *dscene)

intern/cycles/render/light.h

@@ -88,6 +88,9 @@ class LightManager {
   bool use_light_visibility;
   bool need_update;
 
+  /* Need to update background (including multiple importance map) */
+  bool need_update_background;
+
   LightManager();
   ~LightManager();
 
@@ -97,7 +100,7 @@ class LightManager {
   void remove_ies(int slot);
 
   void device_update(Device *device, DeviceScene *dscene, Scene *scene, Progress &progress);
-  void device_free(Device *device, DeviceScene *dscene);
+  void device_free(Device *device, DeviceScene *dscene, const bool free_background = true);
 
   void tag_update(Scene *scene);
 

intern/cycles/render/shader.cpp

@@ -318,9 +318,11 @@ void Shader::tag_update(Scene *scene)
    * has use_mis set to false. We are quite close to release now, so
    * better to be safe.
    */
-  if (this == scene->background->get_shader(scene) &&
-      scene->light_manager->has_background_light(scene)) {
-    scene->light_manager->need_update = true;
+  if (this == scene->background->get_shader(scene)) {
+    scene->light_manager->need_update_background = true;
+    if (scene->light_manager->has_background_light(scene)) {
+      scene->light_manager->need_update = true;
+    }
   }
 
   /* quick detection of which kind of shaders we have to avoid loading