Fix Cycles not correctly using Background.shader if specified

Based on patch by Alex Fuller.

Differential Revision: https://developer.blender.org/D6627

intern/cycles/render/background.cpp

@@ -64,14 +64,7 @@ void Background::device_update(Device *device, DeviceScene *dscene, Scene *scene
 
   device_free(device, dscene);
 
-  Shader *bg_shader = shader;
-
-  if (use_shader) {
-    if (!bg_shader)
-      bg_shader = scene->default_background;
-  }
-  else
-    bg_shader = scene->default_empty;
+  Shader *bg_shader = get_shader(scene);
 
   /* set shader index and transparent option */
   KernelBackground *kbackground = &dscene->data.background;
@@ -134,4 +127,9 @@ void Background::tag_update(Scene *scene)
   need_update = true;
 }
 
+Shader *Background::get_shader(const Scene *scene)
+{
+  return (use_shader) ? ((shader) ? shader : scene->default_background) : scene->default_empty;
+}
+
 CCL_NAMESPACE_END

intern/cycles/render/background.h

@@ -55,6 +55,8 @@ class Background : public Node {
 
   bool modified(const Background &background);
   void tag_update(Scene *scene);
+
+  Shader *get_shader(const Scene *scene);
 };
 
 CCL_NAMESPACE_END

intern/cycles/render/light.cpp

@@ -219,8 +219,7 @@ void LightManager::disable_ineffective_light(Scene *scene)
      * - If unsupported on a device
      * - If we don't need it (no HDRs etc.)
      */
-    Shader *shader = (scene->background->shader) ? scene->background->shader :
-                                                   scene->default_background;
+    Shader *shader = scene->background->get_shader(scene);
     const bool disable_mis = !(has_portal || shader->has_surface_spatial_varying);
     VLOG_IF(1, disable_mis) << "Background MIS has been disabled.\n";
     foreach (Light *light, scene->lights) {
@@ -569,8 +568,7 @@ void LightManager::device_update_background(Device *device,
   int2 res = make_int2(background_light->map_resolution, background_light->map_resolution / 2);
   /* If the resolution isn't set manually, try to find an environment texture. */
   if (res.x == 0) {
-    Shader *shader = (scene->background->shader) ? scene->background->shader :
-                                                   scene->default_background;
+    Shader *shader = scene->background->get_shader(scene);
     foreach (ShaderNode *node, shader->graph->nodes) {
       if (node->type == EnvironmentTextureNode::node_type) {
         EnvironmentTextureNode *env = (EnvironmentTextureNode *)node;

intern/cycles/render/osl.cpp

@@ -16,6 +16,7 @@
 
 #include "device/device.h"
 
+#include "render/background.h"
 #include "render/colorspace.h"
 #include "render/graph.h"
 #include "render/light.h"
@@ -106,6 +107,7 @@ void OSLShaderManager::device_update(Device *device,
 
   /* create shaders */
   OSLGlobals *og = (OSLGlobals *)device->osl_memory();
+  Shader *background_shader = scene->background->get_shader(scene);
 
   foreach (Shader *shader, scene->shaders) {
     assert(shader->graph);
@@ -119,7 +121,7 @@ void OSLShaderManager::device_update(Device *device,
     thread_scoped_lock lock(ss_mutex);
 
     OSLCompiler compiler(this, services, ss, scene);
-    compiler.background = (shader == scene->default_background);
+    compiler.background = (shader == background_shader);
     compiler.compile(og, shader);
 
     if (shader->use_mis && shader->has_surface_emission)
@@ -131,7 +133,7 @@ void OSLShaderManager::device_update(Device *device,
   og->ts = ts;
   og->services = services;
 
-  int background_id = scene->shader_manager->get_shader_id(scene->default_background);
+  int background_id = scene->shader_manager->get_shader_id(background_shader);
   og->background_state = og->surface_state[background_id & SHADER_MASK];
   og->use = true;
 

intern/cycles/render/shader.cpp

@@ -317,7 +317,7 @@ 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->default_background && scene->light_manager->has_background_light(scene)) {
+  if (this == scene->background->get_shader(scene) && scene->light_manager->has_background_light(scene)) {
     scene->light_manager->need_update = true;
   }
 

intern/cycles/render/svm.cpp

@@ -15,6 +15,8 @@
  */
 
 #include "device/device.h"
+
+#include "render/background.h"
 #include "render/graph.h"
 #include "render/light.h"
 #include "render/mesh.h"
@@ -58,7 +60,7 @@ void SVMShaderManager::device_update_shader(Scene *scene,
 
   SVMCompiler::Summary summary;
   SVMCompiler compiler(scene);
-  compiler.background = (shader == scene->default_background);
+  compiler.background = (shader == scene->background->get_shader(scene));
   compiler.compile(shader, *svm_nodes, 0, &summary);
 
   VLOG(2) << "Compilation summary:\n"