1 files changed, 40 insertions, 1 deletions

diff --git a/intern/cycles/scene/film.cpp b/intern/cycles/scene/film.cpp
index e17c839d60b..c3b126544c4 100644
--- a/intern/cycles/scene/film.cpp
+++ b/intern/cycles/scene/film.cpp
@@ -175,6 +175,7 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
   kfilm->pass_volume_direct = PASS_UNUSED;
   kfilm->pass_volume_indirect = PASS_UNUSED;
   kfilm->pass_shadow = PASS_UNUSED;
+  kfilm->pass_lightgroup = PASS_UNUSED;
 
   /* Mark passes as unused so that the kernel knows the pass is inaccessible. */
   kfilm->pass_denoising_normal = PASS_UNUSED;
@@ -189,6 +190,7 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
   bool have_cryptomatte = false;
   bool have_aov_color = false;
   bool have_aov_value = false;
+  bool have_lightgroup = false;
 
   for (size_t i = 0; i < scene->passes.size(); i++) {
     const Pass *pass = scene->passes[i];
@@ -223,6 +225,15 @@ void Film::device_update(Device *device, DeviceScene *dscene, Scene *scene)
       assert(pass->get_type() <= PASS_CATEGORY_BAKE_END);
     }
 
+    if (pass->get_lightgroup() != ustring()) {
+      if (!have_lightgroup) {
+        kfilm->pass_lightgroup = kfilm->pass_stride;
+        have_lightgroup = true;
+      }
+      kfilm->pass_stride += pass->get_info().num_components;
+      continue;
+    }
+
     switch (pass->get_type()) {
       case PASS_COMBINED:
         kfilm->pass_combined = kfilm->pass_stride;
@@ -414,6 +425,26 @@ int Film::get_aov_offset(Scene *scene, string name, bool &is_color)
   return -1;
 }
 
+bool Film::update_lightgroups(Scene *scene)
+{
+  map<ustring, int> lightgroups;
+  int i = 0;
+  foreach (const Pass *pass, scene->passes) {
+    ustring lightgroup = pass->get_lightgroup();
+    if (!lightgroup.empty()) {
+      if (!lightgroups.count(lightgroup)) {
+        lightgroups[lightgroup] = i++;
+      }
+    }
+  }
+  if (scene->lightgroups != lightgroups) {
+    scene->lightgroups = lightgroups;
+    return true;
+  }
+
+  return false;
+}
+
 void Film::update_passes(Scene *scene, bool add_sample_count_pass)
 {
   const Background *background = scene->background;
@@ -580,11 +611,19 @@ void Film::remove_auto_passes(Scene *scene)
 
 static bool compare_pass_order(const Pass *a, const Pass *b)
 {
+  /* On the highest level, sort by number of components.
+   * Within passes of the same component count, sort so that all non-lightgroup passes come first.
+   * Within that group, sort by type. */
   const int num_components_a = a->get_info().num_components;
   const int num_components_b = b->get_info().num_components;
 
   if (num_components_a == num_components_b) {
-    return (a->get_type() < b->get_type());
+    const int is_lightgroup_a = !a->get_lightgroup().empty();
+    const int is_lightgroup_b = !b->get_lightgroup().empty();
+    if (is_lightgroup_a == is_lightgroup_b) {
+      return (a->get_type() < b->get_type());
+    }
+    return is_lightgroup_b;
   }
 
   return num_components_a > num_components_b;