Performance: Draw play head as an overlay

When playing back animations a playhead is updated in all the animation editors.
The drawing of the playhead is part of the drawing of the main region
`RGN_TYPE_WINDOW` that redraws the whole region.

This change will draw the play head and window scrollers when updating the
screen. This affects the Action editor, Timeline, Graph editor, NLA editor and
Sequence editor. There is noticeable speedup when using complex animation files.

Spring 02_020_A.anim.blend fps went from 11.8 to 12.5 when showing a timeline
and a action editor on a Ryzen 1700.

* When playing back animation the markers don't jump up/down when near the
  frame. This could be added back.

Reviewed By: Brecht van Lommel

Differential Revision: https://developer.blender.org/D8066

1 files changed, 42 insertions, 13 deletions

diff --git a/source/blender/windowmanager/intern/wm_draw.c b/source/blender/windowmanager/intern/wm_draw.c
index fa12d6cf974..c0a9d0ac453 100644
--- a/source/blender/windowmanager/intern/wm_draw.c
+++ b/source/blender/windowmanager/intern/wm_draw.c
@@ -69,6 +69,8 @@
 #include "wm_surface.h"
 #include "wm_window.h"
 
+#include "UI_resources.h"
+
 #ifdef WITH_OPENSUBDIV
 #  include "BKE_subsurf.h"
 #endif
@@ -128,6 +130,28 @@ static void wm_paintcursor_draw(bContext *C, ScrArea *area, ARegion *region)
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name Post Draw Region on display handlers
+ * \{ */
+
+static void wm_region_draw_overlay(bContext *C, ScrArea *area, ARegion *region)
+{
+  wmWindowManager *wm = CTX_wm_manager(C);
+  wmWindow *win = CTX_wm_window(C);
+
+  /* Don't draw overlay with locked interface. Drawing could access scene data that another thread
+   * may be modifying. */
+  if (wm->is_interface_locked) {
+    return;
+  }
+
+  wmViewport(&region->winrct);
+  UI_SetTheme(area->spacetype, region->regiontype);
+  region->type->draw_overlay(C, region);
+  wmWindowViewport(win);
+}
+
+/** \} */
+/* -------------------------------------------------------------------- */
 /** \name Internal Utilities
  * \{ */
 
@@ -749,25 +773,30 @@ static void wm_draw_window_onscreen(bContext *C, wmWindow *win, int view)
     }
   }
 
-  /* Draw paint cursors. */
-  if (wm->paintcursors.first) {
-    ED_screen_areas_iter (win, screen, area) {
-      LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
-        if (region->visible && region == screen->active_region) {
-          CTX_wm_area_set(C, area);
-          CTX_wm_region_set(C, region);
+  /* Draw overlays and paint cursors. */
+  ED_screen_areas_iter (win, screen, area) {
+    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
+      if (region->visible) {
+        const bool do_paint_cursor = (wm->paintcursors.first && region == screen->active_region);
+        const bool do_draw_overlay = (region->type && region->type->draw_overlay);
+        if (!(do_paint_cursor || do_draw_overlay)) {
+          continue;
+        }
 
-          /* make region ready for draw, scissor, pixelspace */
+        CTX_wm_area_set(C, area);
+        CTX_wm_region_set(C, region);
+        if (do_draw_overlay) {
+          wm_region_draw_overlay(C, area, region);
+        }
+        if (do_paint_cursor) {
           wm_paintcursor_draw(C, area, region);
-
-          CTX_wm_region_set(C, NULL);
-          CTX_wm_area_set(C, NULL);
         }
+        CTX_wm_region_set(C, NULL);
+        CTX_wm_area_set(C, NULL);
       }
     }
-
-    wmWindowViewport(win);
   }
+  wmWindowViewport(win);
 
   /* Blend in overlapping area regions */
   ED_screen_areas_iter (win, screen, area) {