WM: prevent drag events being continually tested

Click-drag events that weren't handled would continually be tested
for each mouse-motion event.

As well as being redundant, this added the overhead of querying
gizmos twice per motion event.

Now click-drag is only tested once when the drag threshold is reached.

This mitigates T87511, although the single drag test still causes
the snap gizmo to flicker.

3 files changed, 18 insertions, 1 deletions

diff --git a/source/blender/makesdna/DNA_windowmanager_types.h b/source/blender/makesdna/DNA_windowmanager_types.h
index 130b308f224..59091fec4b8 100644
--- a/source/blender/makesdna/DNA_windowmanager_types.h
+++ b/source/blender/makesdna/DNA_windowmanager_types.h
@@ -278,8 +278,14 @@ typedef struct wmWindow {
   char event_queue_check_click;
   /** Enable when #KM_PRESS events are not handled (keyboard/mouse-buttons only). */
   char event_queue_check_drag;
+  /**
+   * Enable when the drag was handled,
+   * to avoid mouse-motion continually triggering drag events which are not handled
+   * but add overhead to gizmo handling (for example), see T87511.
+   */
+  char event_queue_check_drag_handled;
 
-  char _pad0[2];
+  char _pad0[1];
 
   /** Internal, lock pie creation from this event until released. */
   short pie_event_type_lock;
diff --git a/source/blender/windowmanager/intern/wm.c b/source/blender/windowmanager/intern/wm.c
index ae5b6c468f7..46e47ae95c4 100644
--- a/source/blender/windowmanager/intern/wm.c
+++ b/source/blender/windowmanager/intern/wm.c
@@ -186,6 +186,7 @@ static void window_manager_blend_read_data(BlendDataReader *reader, ID *id)
     win->addmousemove = true;
     win->event_queue_check_click = 0;
     win->event_queue_check_drag = 0;
+    win->event_queue_check_drag_handled = 0;
     BLO_read_data_address(reader, &win->stereo3d_format);
 
     /* Multi-view always fallback to anaglyph at file opening
diff --git a/source/blender/windowmanager/intern/wm_event_system.c b/source/blender/windowmanager/intern/wm_event_system.c
index 627ec1d5722..cb4aa3b6549 100644
--- a/source/blender/windowmanager/intern/wm_event_system.c
+++ b/source/blender/windowmanager/intern/wm_event_system.c
@@ -2941,6 +2941,8 @@ static int wm_handlers_do(bContext *C, wmEvent *event, ListBase *handlers)
     if (wm_action_not_handled(action)) {
       if (win->event_queue_check_drag) {
         if (WM_event_drag_test(event, &event->prevclickx)) {
+          win->event_queue_check_drag_handled = true;
+
           int x = event->x;
           int y = event->y;
           short val = event->val;
@@ -2984,6 +2986,7 @@ static int wm_handlers_do(bContext *C, wmEvent *event, ListBase *handlers)
         if (event->is_repeat == false) {
           win->event_queue_check_click = true;
           win->event_queue_check_drag = true;
+          win->event_queue_check_drag_handled = false;
         }
       }
       else if (event->val == KM_RELEASE) {
@@ -3470,6 +3473,13 @@ void wm_event_do_handlers(bContext *C)
         win->event_queue_check_click = false;
       }
 
+      /* If the drag even was handled, don't attempt to keep re-handing the same
+       * drag event on every cursor motion, see: T87511. */
+      if (win->event_queue_check_drag_handled) {
+        win->event_queue_check_drag = false;
+        win->event_queue_check_drag_handled = false;
+      }
+
       /* Update previous mouse position for following events to use. */
       win->eventstate->prevx = event->x;
       win->eventstate->prevy = event->y;