UI: ignore events in empty region overlap areas

- Resizable areas use 2D view bounds.
- Header uses the button bounds.
- A margin is added to avoid clicking between buttons.
- Region resize edges clamp to the 2D view bounds.

Resovles T61554

4 files changed, 157 insertions, 1 deletions

diff --git a/source/blender/editors/screen/CMakeLists.txt b/source/blender/editors/screen/CMakeLists.txt
index daa72ac194c..9576920bcd2 100644
--- a/source/blender/editors/screen/CMakeLists.txt
+++ b/source/blender/editors/screen/CMakeLists.txt
@@ -39,6 +39,7 @@ set(INC_SYS
 
 set(SRC
   area.c
+  area_query.c
   area_utils.c
   glutil.c
   screen_context.c
diff --git a/source/blender/editors/screen/area.c b/source/blender/editors/screen/area.c
index 5923d0373d5..ab68b3cfcf8 100644
--- a/source/blender/editors/screen/area.c
+++ b/source/blender/editors/screen/area.c
@@ -901,33 +901,65 @@ static void fullscreen_azone_initialize(ScrArea *sa, ARegion *ar)
 #define AZONEPAD_ICON (0.45f * U.widget_unit)
 static void region_azone_edge(AZone *az, ARegion *ar)
 {
+  int clip_axis = -1;
   switch (az->edge) {
     case AE_TOP_TO_BOTTOMRIGHT:
       az->x1 = ar->winrct.xmin;
       az->y1 = ar->winrct.ymax - AZONEPAD_EDGE;
       az->x2 = ar->winrct.xmax;
       az->y2 = ar->winrct.ymax + AZONEPAD_EDGE;
+      if (ar->overlap) {
+        clip_axis = 0;
+      }
       break;
     case AE_BOTTOM_TO_TOPLEFT:
       az->x1 = ar->winrct.xmin;
       az->y1 = ar->winrct.ymin + AZONEPAD_EDGE;
       az->x2 = ar->winrct.xmax;
       az->y2 = ar->winrct.ymin - AZONEPAD_EDGE;
+      if (ar->overlap) {
+        clip_axis = 0;
+      }
       break;
     case AE_LEFT_TO_TOPRIGHT:
       az->x1 = ar->winrct.xmin - AZONEPAD_EDGE;
       az->y1 = ar->winrct.ymin;
       az->x2 = ar->winrct.xmin + AZONEPAD_EDGE;
       az->y2 = ar->winrct.ymax;
+      if (ar->overlap) {
+        clip_axis = 1;
+      }
       break;
     case AE_RIGHT_TO_TOPLEFT:
       az->x1 = ar->winrct.xmax + AZONEPAD_EDGE;
       az->y1 = ar->winrct.ymin;
       az->x2 = ar->winrct.xmax - AZONEPAD_EDGE;
       az->y2 = ar->winrct.ymax;
+      if (ar->overlap) {
+        clip_axis = 1;
+      }
       break;
   }
 
+  /* Constrain action zones to usable area of region.
+   * Needed so blank areas of the region are interactive and aciton zones don't get in the way. */
+  if (clip_axis == 0) {
+    az->x1 = max_ii(az->x1,
+                    (ar->winrct.xmin + UI_view2d_view_to_region_x(&ar->v2d, ar->v2d.tot.xmin)) -
+                        UI_REGION_OVERLAP_MARGIN);
+    az->x2 = min_ii(az->x2,
+                    (ar->winrct.xmin + UI_view2d_view_to_region_x(&ar->v2d, ar->v2d.tot.xmax)) +
+                        UI_REGION_OVERLAP_MARGIN);
+  }
+  else if (clip_axis == 1) {
+    az->y1 = max_ii(az->y1,
+                    (ar->winrct.ymin + UI_view2d_view_to_region_y(&ar->v2d, ar->v2d.tot.ymin)) -
+                        UI_REGION_OVERLAP_MARGIN);
+    az->y2 = min_ii(az->y2,
+                    (ar->winrct.ymin + UI_view2d_view_to_region_y(&ar->v2d, ar->v2d.tot.ymax)) +
+                        UI_REGION_OVERLAP_MARGIN);
+  }
+
   BLI_rcti_init(&az->rect, az->x1, az->x2, az->y1, az->y2);
 }
 
diff --git a/source/blender/editors/screen/area_query.c b/source/blender/editors/screen/area_query.c
new file mode 100644
index 00000000000..a4bcf622815
--- /dev/null
+++ b/source/blender/editors/screen/area_query.c
@@ -0,0 +1,123 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup edscr
+ *
+ * Query functions for area/region.
+ */
+
+#include "DNA_userdef_types.h"
+
+#include "BLI_blenlib.h"
+#include "BLI_utildefines.h"
+
+#include "RNA_types.h"
+
+#include "WM_api.h"
+
+#include "ED_screen.h"
+
+#include "UI_interface.h"
+#include "UI_view2d.h"
+
+bool ED_region_overlap_isect_x(const ARegion *ar, const int event_x)
+{
+  BLI_assert(ar->overlap);
+  /* No contents, skip it. */
+  if (ar->v2d.mask.xmin == ar->v2d.mask.xmax) {
+    return false;
+  }
+  return BLI_rctf_isect_x(&ar->v2d.tot,
+                          UI_view2d_region_to_view_x(&ar->v2d, event_x - ar->winrct.xmin));
+}
+
+bool ED_region_overlap_isect_y(const ARegion *ar, const int event_y)
+{
+  BLI_assert(ar->overlap);
+  /* No contents, skip it. */
+  if (ar->v2d.mask.ymin == ar->v2d.mask.ymax) {
+    return false;
+  }
+  return BLI_rctf_isect_y(&ar->v2d.tot,
+                          UI_view2d_region_to_view_y(&ar->v2d, event_y - ar->winrct.ymin));
+}
+
+bool ED_region_overlap_isect_xy(const ARegion *ar, const int event_xy[2])
+{
+  return (ED_region_overlap_isect_x(ar, event_xy[0]) &&
+          ED_region_overlap_isect_y(ar, event_xy[1]));
+}
+
+bool ED_region_overlap_isect_x_with_margin(const ARegion *ar, const int event_x, const int margin)
+{
+  BLI_assert(ar->overlap);
+  /* No contents, skip it. */
+  if (ar->v2d.mask.xmin == ar->v2d.mask.xmax) {
+    return false;
+  }
+  int region_x = event_x - ar->winrct.xmin;
+  return ((ar->v2d.tot.xmin <= UI_view2d_region_to_view_x(&ar->v2d, region_x + margin)) &&
+          (ar->v2d.tot.xmax >= UI_view2d_region_to_view_x(&ar->v2d, region_x - margin)));
+}
+
+bool ED_region_overlap_isect_y_with_margin(const ARegion *ar, const int event_y, const int margin)
+{
+  BLI_assert(ar->overlap);
+  /* No contents, skip it. */
+  if (ar->v2d.mask.ymin == ar->v2d.mask.ymax) {
+    return false;
+  }
+  int region_y = event_y - ar->winrct.ymin;
+  return ((ar->v2d.tot.ymin <= UI_view2d_region_to_view_y(&ar->v2d, region_y + margin)) &&
+          (ar->v2d.tot.ymax >= UI_view2d_region_to_view_y(&ar->v2d, region_y - margin)));
+}
+
+bool ED_region_overlap_isect_xy_with_margin(const ARegion *ar,
+                                            const int event_xy[2],
+                                            const int margin)
+{
+  return (ED_region_overlap_isect_x_with_margin(ar, event_xy[0], margin) &&
+          ED_region_overlap_isect_y_with_margin(ar, event_xy[1], margin));
+}
+
+bool ED_region_contains_xy(const ARegion *ar, const int event_xy[2])
+{
+  /* Only use the margin when inside the region. */
+  if (BLI_rcti_isect_pt_v(&ar->winrct, event_xy)) {
+    if (ar->overlap) {
+      const int overlap_margin = UI_REGION_OVERLAP_MARGIN;
+      /* Note the View2D.tot isn't reliable for headers with spacers otherwise
+       * we'd check #ED_region_overlap_isect_xy_with_margin for both bases. */
+      if (ar->v2d.keeptot == V2D_KEEPTOT_STRICT) {
+        /* Header. */
+        rcti rect;
+        BLI_rcti_init_pt_radius(&rect, event_xy, overlap_margin);
+        if (UI_region_but_find_rect_over(ar, &rect) == NULL) {
+          return false;
+        }
+      }
+      else {
+        /* Side-bar & any other kind of overlapping region. */
+        if (!ED_region_overlap_isect_xy_with_margin(ar, event_xy, overlap_margin)) {
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+  return false;
+}
diff --git a/source/blender/editors/screen/screen_edit.c b/source/blender/editors/screen/screen_edit.c
index 95bade1da64..50f0ab9b96b 100644
--- a/source/blender/editors/screen/screen_edit.c
+++ b/source/blender/editors/screen/screen_edit.c
@@ -683,7 +683,7 @@ void ED_screen_set_active_region(bContext *C, wmWindow *win, const int xy[2])
     if (sa) {
       /* make overlap active when mouse over */
       for (ar = sa->regionbase.first; ar; ar = ar->next) {
-        if (BLI_rcti_isect_pt_v(&ar->winrct, xy)) {
+        if (ED_region_contains_xy(ar, xy)) {
           scr->active_region = ar;
           break;
         }