Cycles: enable improved closure sampling, this should give less noise for mix, add

and glass shaders. How well this will work on non-fermi GPU's is unclear still, it's
a bit heavy on register usage.

intern/cycles/device/device.cpp

@@ -157,6 +157,8 @@ Device *Device::create(DeviceType type, bool background, int threads)
 			return NULL;
 	}
 
+	device->device_type = type;
+
 	return device;
 }
 

intern/cycles/device/device.h

@@ -75,12 +75,14 @@ class Device {
 protected:
 	Device() {}
 
-	DeviceType type;
+	DeviceType device_type;
 	bool background;
 
 public:
 	virtual ~Device() {}
 
+	DeviceType type() { return device_type; }
+
 	/* info */
 	virtual string description() = 0;
 

intern/cycles/kernel/kernel_types.h

@@ -44,7 +44,7 @@ CCL_NAMESPACE_BEGIN
 #define __EMISSION__
 #define __TEXTURES__
 #define __HOLDOUT__
-//#define __MULTI_CLOSURE__
+#define __MULTI_CLOSURE__
 //#define __TRANSPARENT_SHADOWS__
 //#define __MULTI_LIGHT__
 #endif

intern/cycles/render/scene.h

@@ -109,7 +109,7 @@ public:
 	SceneParams()
 	{
 		shadingsystem = SVM;
-		use_multi_closure = false;
+		use_multi_closure = true;
 		bvh_type = BVH_DYNAMIC;
 		use_bvh_cache = false;
 		use_bvh_spatial_split = false;

intern/cycles/render/svm.cpp

@@ -58,6 +58,7 @@ void SVMShaderManager::device_update(Device *device, DeviceScene *dscene, Scene
 	}
 	
 	bool sunsky_done = false;
+	bool use_multi_closure = (scene->params.use_multi_closure && device->type() != DEVICE_OPENCL);
 
 	for(i = 0; i < scene->shaders.size(); i++) {
 		Shader *shader = scene->shaders[i];
@@ -70,7 +71,7 @@ void SVMShaderManager::device_update(Device *device, DeviceScene *dscene, Scene
 			scene->light_manager->need_update = true;
 
 		SVMCompiler compiler(scene->shader_manager, scene->image_manager,
-			scene->params.use_multi_closure);
+			use_multi_closure);
 		compiler.sunsky = (sunsky_done)? NULL: &dscene->data.sunsky;
 		compiler.background = ((int)i == scene->default_background);
 		compiler.compile(shader, svm_nodes, i);