7 files changed, 80 insertions, 6 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index 5f65fd7506b..094d68e4f53 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -519,6 +519,18 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
                 min=0.0, max=5.0
                 )
 
+        cls.motion_blur_position = EnumProperty(
+            name="Motion Blur Position",
+            default='CENTER',
+            description="Specifies an offset for the shutter’s time interval "
+                        "which allows to change the motion blur trails",
+            items=(
+                ('START', "Start on Frame", "The shutter opens at the current frame"),
+                ('CENTER', "Center on Frame", "The shutter is open during the current frame"),
+                ('END', "End on Frame", "The shutter closes at the current frame"),
+                ),
+            )
+
     @classmethod
     def unregister(cls):
         del bpy.types.Scene.cycles
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index ecd98551747..3700da3263e 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -259,11 +259,14 @@ class CyclesRender_PT_motion_blur(CyclesButtonsPanel, Panel):
     def draw(self, context):
         layout = self.layout
 
-        rd = context.scene.render
+        scene = context.scene
+        cscene = scene.cycles
+        rd = scene.render
         layout.active = rd.use_motion_blur
 
-        row = layout.row()
-        row.prop(rd, "motion_blur_shutter")
+        col = layout.column()
+        col.prop(cscene, "motion_blur_position", text="Position")
+        col.prop(rd, "motion_blur_shutter")
 
 
 class CyclesRender_PT_film(CyclesButtonsPanel, Panel):
diff --git a/intern/cycles/blender/blender_camera.cpp b/intern/cycles/blender/blender_camera.cpp
index 1cc601ce148..04926f94c62 100644
--- a/intern/cycles/blender/blender_camera.cpp
+++ b/intern/cycles/blender/blender_camera.cpp
@@ -36,6 +36,7 @@ struct BlenderCamera {
 
 	float lens;
 	float shuttertime;
+	Camera::MotionPosition motion_position;
 
 	float aperturesize;
 	uint apertureblades;
@@ -83,6 +84,7 @@ static void blender_camera_init(BlenderCamera *bcam, BL::RenderSettings b_render
 	bcam->sensor_height = 18.0f;
 	bcam->sensor_fit = BlenderCamera::AUTO;
 	bcam->shuttertime = 1.0f;
+	bcam->motion_position = Camera::MOTION_POSITION_CENTER;
 	bcam->border.right = 1.0f;
 	bcam->border.top = 1.0f;
 	bcam->pano_viewplane.right = 1.0f;
@@ -409,6 +411,7 @@ static void blender_camera_sync(Camera *cam, BlenderCamera *bcam, int width, int
 	cam->shuttertime = bcam->shuttertime;
 	cam->fov_pre = cam->fov;
 	cam->fov_post = cam->fov;
+	cam->motion_position = bcam->motion_position;
 
 	/* border */
 	cam->border = bcam->border;
@@ -431,6 +434,22 @@ void BlenderSync::sync_camera(BL::RenderSettings b_render, BL::Object b_override
 	bcam.pixelaspect.y = b_render.pixel_aspect_y();
 	bcam.shuttertime = b_render.motion_blur_shutter();
 
+	PointerRNA cscene = RNA_pointer_get(&b_scene.ptr, "cycles");
+	switch(RNA_enum_get(&cscene, "motion_blur_position")) {
+		case 0:
+			bcam.motion_position = Camera::MOTION_POSITION_START;
+			break;
+		case 1:
+			bcam.motion_position = Camera::MOTION_POSITION_CENTER;
+			break;
+		case 2:
+			bcam.motion_position = Camera::MOTION_POSITION_END;
+			break;
+		default:
+			bcam.motion_position = Camera::MOTION_POSITION_CENTER;
+			break;
+	}
+
 	/* border */
 	if(b_render.use_border()) {
 		bcam.border.left = b_render.border_min_x();
diff --git a/intern/cycles/blender/blender_object.cpp b/intern/cycles/blender/blender_object.cpp
index 7dc57c33ed3..11593807a00 100644
--- a/intern/cycles/blender/blender_object.cpp
+++ b/intern/cycles/blender/blender_object.cpp
@@ -685,6 +685,28 @@ void BlenderSync::sync_motion(BL::RenderSettings b_render,
 	Camera prevcam = *(scene->camera);
 
 	int frame_center = b_scene.frame_current();
+	float frame_center_delta = 0.0f;
+
+	if(scene->need_motion() != Scene::MOTION_PASS &&
+	   scene->camera->motion_position != Camera::MOTION_POSITION_CENTER)
+	{
+		float shuttertime = scene->camera->shuttertime;
+		if(scene->camera->motion_position == Camera::MOTION_POSITION_END) {
+			frame_center_delta = -shuttertime * 0.5f;
+		}
+		else {
+			assert(scene->camera->motion_position == Camera::MOTION_POSITION_START);
+			frame_center_delta = shuttertime * 0.5f;
+		}
+		float time = frame_center + frame_center_delta;
+		int frame = (int)floorf(time);
+		float subframe = time - frame;
+		python_thread_state_restore(python_thread_state);
+		b_engine.frame_set(frame, subframe);
+		python_thread_state_save(python_thread_state);
+		sync_camera_motion(b_render, b_cam, width, height, 0.0f);
+		sync_objects(b_v3d, 0.0f);
+	}
 
 	/* always sample these times for camera motion */
 	motion_times.insert(-1.0f);
@@ -704,7 +726,7 @@ void BlenderSync::sync_motion(BL::RenderSettings b_render,
 			shuttertime = scene->camera->shuttertime;
 
 		/* compute frame and subframe time */
-		float time = frame_center + relative_time * shuttertime * 0.5f;
+		float time = frame_center + frame_center_delta + relative_time * shuttertime * 0.5f;
 		int frame = (int)floorf(time);
 		float subframe = time - frame;
 
diff --git a/intern/cycles/blender/blender_sync.cpp b/intern/cycles/blender/blender_sync.cpp
index aed1b6de138..986e90c59f7 100644
--- a/intern/cycles/blender/blender_sync.cpp
+++ b/intern/cycles/blender/blender_sync.cpp
@@ -161,7 +161,12 @@ void BlenderSync::sync_data(BL::RenderSettings b_render,
 
 	mesh_synced.clear(); /* use for objects and motion sync */
 
-	sync_objects(b_v3d);
+	if(scene->need_motion() == Scene::MOTION_PASS ||
+	   scene->need_motion() == Scene::MOTION_NONE ||
+	   scene->camera->motion_position == Camera::MOTION_POSITION_CENTER)
+	{
+		sync_objects(b_v3d);
+	}
 	sync_motion(b_render,
 	            b_v3d,
 	            b_override,
diff --git a/intern/cycles/render/camera.cpp b/intern/cycles/render/camera.cpp
index 127d116e556..88ff7fbb70a 100644
--- a/intern/cycles/render/camera.cpp
+++ b/intern/cycles/render/camera.cpp
@@ -29,6 +29,7 @@ CCL_NAMESPACE_BEGIN
 Camera::Camera()
 {
 	shuttertime = 1.0f;
+	motion_position = MOTION_POSITION_CENTER;
 
 	aperturesize = 0.0f;
 	focaldistance = 10.0f;
diff --git a/intern/cycles/render/camera.h b/intern/cycles/render/camera.h
index 1bedb051112..53bd4f0bc14 100644
--- a/intern/cycles/render/camera.h
+++ b/intern/cycles/render/camera.h
@@ -32,12 +32,24 @@ class Scene;
 /* Camera
  *
  * The camera parameters are quite standard, tested to be both compatible with
- * Renderman, and Blender after remapping. */
+ * Renderman, and Blender after remapping.
+ */
 
 class Camera {
 public:
+	/* Specifies an offset for the shutter's time interval. */
+	enum MotionPosition {
+		/* Shutter opens at the current frame. */
+		MOTION_POSITION_START,
+		/* Shutter is fully open at the current frame. */
+		MOTION_POSITION_CENTER,
+		/* Shutter closes at the current frame. */
+		MOTION_POSITION_END,
+	};
+
 	/* motion blur */
 	float shuttertime;
+	MotionPosition motion_position;
 
 	/* depth of field */
 	float focaldistance;