Fix T63588: Cycles unnecessarily updates background importance sampling map

With modifications by Brecht to solve T77273, crash enabling portal lights.

1 files changed, 5 insertions, 3 deletions

diff --git a/intern/cycles/render/shader.cpp b/intern/cycles/render/shader.cpp
index 8403a636e1c..39ba45a751a 100644
--- a/intern/cycles/render/shader.cpp
+++ b/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