Cycles: Expose "Max Bounces" for the world light.

When using MIS, the world is treated as regular light and in this case
we can now also limit the maximum amount of bounces, the background light
will contribute to the scene.

This can improve performance in some cases, where it's e.g. sufficient to
only have a contribution on first 1-2 bounces.
Examples can be found in the differential.

Differential revision: https://developer.blender.org/D1399

3 files changed, 8 insertions, 0 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index 16a807b3af5..87c0f7c154a 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -739,6 +739,12 @@ class CyclesWorldSettings(bpy.types.PropertyGroup):
                 min=1, max=10000,
                 default=4,
                 )
+        cls.max_bounces = IntProperty(
+                name="Max Bounces",
+                description="Maximum number of bounces the background light will contribute to the render",
+                min=0, max=1024,
+                default=1024,
+                )
         cls.homogeneous_volume = BoolProperty(
                 name="Homogeneous Volume",
                 description="When using volume rendering, assume volume has the same density everywhere"
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index f6ff86ac30e..f7179e2472b 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -1040,6 +1040,7 @@ class CyclesWorld_PT_settings(CyclesButtonsPanel, Panel):
         sub.prop(cworld, "sample_map_resolution")
         if use_branched_path(context):
             sub.prop(cworld, "samples")
+        sub.prop(cworld, "max_bounces")
 
         col = split.column()
         col.label(text="Volume:")
diff --git a/intern/cycles/blender/blender_object.cpp b/intern/cycles/blender/blender_object.cpp
index 1e17d306fd0..9fa1b35d2ad 100644
--- a/intern/cycles/blender/blender_object.cpp
+++ b/intern/cycles/blender/blender_object.cpp
@@ -215,6 +215,7 @@ void BlenderSync::sync_background_light(bool use_portal)
 				light->map_resolution  = get_int(cworld, "sample_map_resolution");
 				light->shader = scene->default_background;
 				light->use_mis = sample_as_light;
+				light->max_bounces = get_int(cworld, "max_bounces");
 
 				int samples = get_int(cworld, "samples");
 				if(get_boolean(cscene, "use_square_samples"))