5 files changed, 28 insertions, 3 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index 62c1db5a16d..b2d982fdabc 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -36,6 +36,9 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
             default=10, min=1, max=2147483647)
         cls.preview_passes = IntProperty(name="Preview Passes", description="Number of passes to render in the viewport, unlimited if 0",
             default=0, min=0, max=2147483647)
+        cls.preview_pause = BoolProperty(name="Pause Preview", description="Pause all viewport preview renders",
+            default=False)
+
         cls.min_bounces = IntProperty(name="Min Bounces", description="Minimum number of bounces",
             default=3, min=0, max=1024)
         cls.max_bounces = IntProperty(name="Max Bounces", description="Maximum number of bounces",
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index 4fe9e25d251..ec753590cce 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -473,6 +473,17 @@ def draw_device(self, context):
         if cscene.device == 'CPU' and engine.with_osl():
             layout.prop(cscene, "shading_system")
 
+def draw_pause(self, context):
+    layout = self.layout
+    scene = context.scene
+
+    if scene.render.engine == "CYCLES":
+        view = context.space_data
+
+        if view.viewport_shade == "RENDERED":
+            cscene = scene.cycles
+            layout.prop(cscene, "preview_pause", icon="PAUSE", text="")
+
 def get_panels():
     return [
         bpy.types.RENDER_PT_render,
@@ -514,12 +525,14 @@ def get_panels():
 
 def register():
     bpy.types.RENDER_PT_render.append(draw_device)
+    bpy.types.VIEW3D_HT_header.append(draw_pause)
 
     for panel in get_panels():
         panel.COMPAT_ENGINES.add('CYCLES')
     
 def unregister():
     bpy.types.RENDER_PT_render.remove(draw_device)
+    bpy.types.VIEW3D_HT_header.remove(draw_pause)
 
     for panel in get_panels():
         panel.COMPAT_ENGINES.remove('CYCLES')
diff --git a/intern/cycles/blender/blender_session.cpp b/intern/cycles/blender/blender_session.cpp
index 7be15ca0e3c..62721b7cf10 100644
--- a/intern/cycles/blender/blender_session.cpp
+++ b/intern/cycles/blender/blender_session.cpp
@@ -93,6 +93,7 @@ void BlenderSession::create_session()
 	session->scene = scene;
 	session->progress.set_update_callback(function_bind(&BlenderSession::tag_redraw, this));
 	session->progress.set_cancel_callback(function_bind(&BlenderSession::test_cancel, this));
+	session->set_pause(BlenderSync::get_session_pause(b_scene, background));
 
 	/* start rendering */
 	session->reset(width, height, session_params.passes);
@@ -159,6 +160,7 @@ void BlenderSession::synchronize()
 
 	/* increase passes, but never decrease */
 	session->set_passes(session_params.passes);
+	session->set_pause(BlenderSync::get_session_pause(b_scene, background));
 
 	/* copy recalc flags, outside of mutex so we can decide to do the real
 	   synchronization at a later time to not block on running updates */
@@ -178,12 +180,12 @@ void BlenderSession::synchronize()
 	else
 		sync->sync_camera(width, height);
 
+	/* unlock */
+	session->scene->mutex.unlock();
+
 	/* reset if needed */
 	if(scene->need_reset())
 		session->reset(width, height, session_params.passes);
-
-	/* unlock */
-	session->scene->mutex.unlock();
 }
 
 bool BlenderSession::draw(int w, int h)
diff --git a/intern/cycles/blender/blender_sync.cpp b/intern/cycles/blender/blender_sync.cpp
index ccfc3bb2bf1..c579253336f 100644
--- a/intern/cycles/blender/blender_sync.cpp
+++ b/intern/cycles/blender/blender_sync.cpp
@@ -185,6 +185,12 @@ SceneParams BlenderSync::get_scene_params(BL::Scene b_scene)
 
 /* Session Parameters */
 
+bool BlenderSync::get_session_pause(BL::Scene b_scene, bool background)
+{
+	PointerRNA cscene = RNA_pointer_get(&b_scene.ptr, "cycles");
+	return (background)? false: get_boolean(cscene, "preview_pause");
+}
+
 SessionParams BlenderSync::get_session_params(BL::Scene b_scene, bool background)
 {
 	SessionParams params;
diff --git a/intern/cycles/blender/blender_sync.h b/intern/cycles/blender/blender_sync.h
index 16ce1998a24..fe60f42bc75 100644
--- a/intern/cycles/blender/blender_sync.h
+++ b/intern/cycles/blender/blender_sync.h
@@ -61,6 +61,7 @@ public:
 	/* get parameters */
 	static SceneParams get_scene_params(BL::Scene b_scene);
 	static SessionParams get_session_params(BL::Scene b_scene, bool background);
+	static bool get_session_pause(BL::Scene b_scene, bool background);
 
 private:
 	/* sync */