Fix T78688: Crash changing workspace with specific fullscreen setup

When switching workspaces we need to have an unused screen layout that
we can activate. The other window now showed the only available screen
layout in fullscreen though.
Usually when there's no unused screen layout we duplicate an existing
one, but that code didn't respect the fullscreen case properly.

This also tries to clean up the logic a bit, but things are still rather
complicated to follow.

Changes in this code are always risky. Of course things worked fine in
my tests, but I wouldn't be surprised if something breaks.

1 files changed, 14 insertions, 35 deletions

diff --git a/source/blender/editors/screen/screen_edit.c b/source/blender/editors/screen/screen_edit.c
index 81afb06ac27..62720d8ca37 100644
--- a/source/blender/editors/screen/screen_edit.c
+++ b/source/blender/editors/screen/screen_edit.c
@@ -985,39 +985,14 @@ void ED_screen_global_areas_refresh(wmWindow *win)
 /* -------------------------------------------------------------------- */
 /* Screen changing */
 
-static bScreen *screen_fullscreen_find_associated_normal_screen(const Main *bmain, bScreen *screen)
-{
-  for (bScreen *screen_iter = bmain->screens.first; screen_iter;
-       screen_iter = screen_iter->id.next) {
-    if ((screen_iter != screen) && ELEM(screen_iter->state, SCREENMAXIMIZED, SCREENFULL)) {
-      ScrArea *area = screen_iter->areabase.first;
-      if (area && area->full == screen) {
-        return screen_iter;
-      }
-    }
-  }
-
-  return screen;
-}
-
 /**
  * \return the screen to activate.
  * \warning The returned screen may not always equal \a screen_new!
  */
-bScreen *screen_change_prepare(
+void screen_change_prepare(
     bScreen *screen_old, bScreen *screen_new, Main *bmain, bContext *C, wmWindow *win)
 {
-  /* validate screen, it's called with notifier reference */
-  if (BLI_findindex(&bmain->screens, screen_new) == -1) {
-    return NULL;
-  }
-
-  screen_new = screen_fullscreen_find_associated_normal_screen(bmain, screen_new);
-
-  /* check for valid winid */
-  if (!(screen_new->winid == 0 || screen_new->winid == win->winid)) {
-    return NULL;
-  }
+  BLI_assert(BLI_findindex(&bmain->screens, screen_new) != -1);
 
   if (screen_old != screen_new) {
     wmTimer *wt = screen_old->animtimer;
@@ -1038,11 +1013,7 @@ bScreen *screen_change_prepare(
     if (wt) {
       screen_new->animtimer = wt;
     }
-
-    return screen_new;
   }
-
-  return NULL;
 }
 
 void screen_change_update(bContext *C, wmWindow *win, bScreen *screen)
@@ -1075,12 +1046,20 @@ bool ED_screen_change(bContext *C, bScreen *screen)
 {
   Main *bmain = CTX_data_main(C);
   wmWindow *win = CTX_wm_window(C);
+  WorkSpace *workspace = BKE_workspace_active_get(win->workspace_hook);
+  WorkSpaceLayout *layout = BKE_workspace_layout_find(workspace, screen);
   bScreen *screen_old = CTX_wm_screen(C);
-  bScreen *screen_new = screen_change_prepare(screen_old, screen, bmain, C, win);
 
-  if (screen_new) {
-    WorkSpace *workspace = BKE_workspace_active_get(win->workspace_hook);
-    WM_window_set_active_screen(win, workspace, screen);
+  /* Get the actual layout/screen to be activated (guaranteed to be unused, even if that means
+   * having to duplicate an existing one). */
+  WorkSpaceLayout *layout_new = ED_workspace_screen_change_ensure_unused_layout(
+      bmain, workspace, layout, layout, win);
+  bScreen *screen_new = BKE_workspace_layout_screen_get(layout_new);
+
+  screen_change_prepare(screen_old, screen_new, bmain, C, win);
+
+  if (screen_old != screen_new) {
+    WM_window_set_active_screen(win, workspace, screen_new);
     screen_change_update(C, win, screen_new);
 
     return true;