Nav: Added a way for code to cancel Alt for menu toggle (ImGuiNavInput_KeyMenu_). Cancelling out on platform window. close request. (#1542, #787)

imgui.cpp

@@ -5296,6 +5296,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         if (p_open != NULL && window->Viewport->PlatformRequestClose && window->Viewport != GetMainViewport())
         {
             window->Viewport->PlatformRequestClose = false;
+            g.NavWindowingToggleLayer = false; // Assume user mapped PlatformRequestClose on ALT-F4 so we disable ALT for menu toggle. False positive not an issue.
             *p_open = false;
         }
 
@@ -8572,7 +8573,9 @@ static void ImGui::NavUpdateWindowing()
 
     // Keyboard: Press and Release ALT to toggle menu layer
     // FIXME: We lack an explicit IO variable for "is the imgui window focused", so compare mouse validity to detect the common case of back-end clearing releases all keys on ALT-TAB
-    if ((g.ActiveId == 0 || g.ActiveIdAllowOverlap) && IsNavInputPressed(ImGuiNavInput_KeyMenu_, ImGuiInputReadMode_Released))
+    if (IsNavInputPressed(ImGuiNavInput_KeyMenu_, ImGuiInputReadMode_Pressed))
+        g.NavWindowingToggleLayer = true;
+    if ((g.ActiveId == 0 || g.ActiveIdAllowOverlap) && g.NavWindowingToggleLayer && IsNavInputPressed(ImGuiNavInput_KeyMenu_, ImGuiInputReadMode_Released))
         if (IsMousePosValid(&g.IO.MousePos) == IsMousePosValid(&g.IO.MousePosPrev))
             apply_toggle_layer = true;