Nav: Fixed single frame CTRL+Tab from properly enabling the menu layer of target window if it doesn't have other active layers.

docs/CHANGELOG.txt

@@ -55,6 +55,8 @@ Other Changes:
 - Nav, InputText: Fixed accidental menu toggling while typing non-ascii characters using AltGR. [@rokups] (#370)
 - Nav: Fixed using SetItemDefaultFocus() on windows with _NavFlattened flag. (#787)
 - Nav: Fixed Tabbing initial activation from skipping the first item if it is tabbable through. (#787)
+- Nav: Fixed fast CTRL+Tab (where keys are only held for one single frame) from properly enabling the
+  menu layer of target window if it doesn't have other active layers.
 - Tables: Expose TableSetColumnEnabled() in public api. (#3935)
 - Tables: Better preserve widths when columns count changes. (#4046)
 - Tables: Sharing more memory buffers between tables, reducing general memory footprints. (#3740)

imgui.cpp

@@ -9668,8 +9668,13 @@ static void ImGui::NavUpdateWindowing()
             NavInitWindow(apply_focus_window, false);
 
         // If the window has ONLY a menu layer (no main layer), select it directly
-        // FIXME-NAV: This should be done in NavInit.. or in FocusWindow..
+        // Use NavLayersActiveMaskNext since windows didn't have a chance to be Begin()-ed on this frame,
-        if (apply_focus_window->DC.NavLayersActiveMask == (1 << ImGuiNavLayer_Menu))
+        // so CTRL+Tab where the keys are only held for 1 frame will be able to use correct layers mask since
+        // the target window as already been previewed once.
+        // FIXME-NAV: This should be done in NavInit.. or in FocusWindow... However in both of those cases,
+        // we won't have a guarantee that windows has been visible before and therefore NavLayersActiveMask*
+        // won't be valid.
+        if (apply_focus_window->DC.NavLayersActiveMaskNext == (1 << ImGuiNavLayer_Menu))
             g.NavLayer = ImGuiNavLayer_Menu;
     }
     if (apply_focus_window)