Fix for multiple modifier stack calculations per frame.

Since 2.5x blender has been using CD_MASK_BAREMESH for updating objects since object_handle_update() no longer has access to G.curscreen to calculate the mask from viewports.

The problem with this is after an initial calculation, CD_MASK_MTFACE may be required on draw, so it would recalculate the modifier stack multiple times per frame.
One case which caused this is armature animated mesh with texface in a dupligroup.

Fix this by having customdata_mask member in the scene, this isn't great design but at least fixes the bug and only changes a few files.

source/blender/blenkernel/intern/object.c

@@ -2550,12 +2550,12 @@ void object_handle_update(Scene *scene, Object *ob)
 			case OB_MESH:
 				{
 					EditMesh *em = (ob == scene->obedit)? BKE_mesh_get_editmesh(ob->data): NULL;
-						// here was vieweditdatamask? XXX
+					BKE_assert((scene->customdata_mask & CD_MASK_BAREMESH) == CD_MASK_BAREMESH);
 					if(em) {
-						makeDerivedMesh(scene, ob, em, CD_MASK_BAREMESH);
+						makeDerivedMesh(scene, ob, em,  scene->customdata_mask); /* was CD_MASK_BAREMESH */
 						BKE_mesh_end_editmesh(ob->data, em);
 					} else
-						makeDerivedMesh(scene, ob, NULL, CD_MASK_BAREMESH);
+						makeDerivedMesh(scene, ob, NULL, scene->customdata_mask);
 				}
 				break;
 

source/blender/blenkernel/intern/scene.c

@@ -946,6 +946,7 @@ float BKE_curframe(Scene *scene)
 static void scene_update_tagged_recursive(Main *bmain, Scene *scene, Scene *scene_parent)
 {
 	Base *base;
+	scene->customdata_mask= scene_parent->customdata_mask;
 
 	/* sets first, we allow per definition current scene to have
 	   dependencies on sets, but not the other way around. */

source/blender/editors/include/ED_view3d.h

@@ -170,5 +170,7 @@ struct ImBuf *ED_view3d_draw_offscreen_imbuf_simple(Scene *scene, int width, int
 Base *ED_view3d_give_base_under_cursor(struct bContext *C, short *mval);
 void ED_view3d_quadview_update(struct ScrArea *sa, struct ARegion *ar, short do_clip);
 
+unsigned int ED_viewedit_datamask(struct bScreen *screen);
+
 #endif /* ED_VIEW3D_H */
 

source/blender/editors/space_view3d/view3d_draw.c

@@ -1950,8 +1950,10 @@ static void gpu_update_lamps_shadows(Scene *scene, View3D *v3d)
 /* *********************** customdata **************** */
 
 /* goes over all modes and view3d settings */
-static CustomDataMask get_viewedit_datamask(bScreen *screen, Scene *scene, Object *ob)
+CustomDataMask ED_viewedit_datamask(bScreen *screen)
 {
+	Scene *scene= screen->scene;
+	Object *ob= scene->basact ? scene->basact->object : NULL;
 	CustomDataMask mask = CD_MASK_BAREMESH;
 	ScrArea *sa;
 	
@@ -2301,11 +2303,10 @@ void view3d_main_area_draw(const bContext *C, ARegion *ar)
 	Object *ob;
 	float backcol[3];
 	unsigned int lay_used;
-	Object *obact = OBACT;
 	const char *grid_unit= NULL;
 
 	/* from now on all object derived meshes check this */
-	v3d->customdata_mask= get_viewedit_datamask(CTX_wm_screen(C), scene, obact);
+	v3d->customdata_mask= scene->customdata_mask;
 
 	/* shadow buffers, before we setup matrices */
 	if(draw_glsl_material(scene, NULL, v3d, v3d->drawtype))

source/blender/makesdna/DNA_scene_types.h

@@ -773,7 +773,7 @@ typedef struct Scene {
 	
 	unsigned int lay;			/* bitflags for layer visibility */
 	int layact;		/* active layer */
-	int pad1;
+	unsigned int customdata_mask;	/* XXX. runtime flag for drawing, actually belongs in the window, only used by object_handle_update() */
 	
 	short flag;								/* various settings */
 	

source/blender/windowmanager/intern/wm_event_system.c

@@ -56,6 +56,7 @@
 #include "ED_fileselect.h"
 #include "ED_info.h"
 #include "ED_screen.h"
+#include "ED_view3d.h"
 #include "ED_util.h"
 
 #include "RNA_access.h"
@@ -296,6 +297,10 @@ void wm_event_do_notifiers(bContext *C)
 		/* XXX make lock in future, or separated derivedmesh users in scene */
 		if(!G.rendering)
 			/* depsgraph & animation: update tagged datablocks */
+
+			/* copied to set's in scene_update_tagged_recursive() */
+			win->screen->scene->customdata_mask= ED_viewedit_datamask(win->screen);
+
 			scene_update_tagged(CTX_data_main(C), win->screen->scene);
 	}