BeginMainMenuBar(): remove expectation that we don't know menu bar height ahead, allowing up to generalize placement in any direction (will be done in master)

Amend 75de34e281

imgui.cpp

@@ -943,7 +943,6 @@ static void             UpdateViewportsEndFrame();
 static void             UpdateSelectWindowViewport(ImGuiWindow* window);
 static bool             UpdateTryMergeWindowIntoHostViewport(ImGuiWindow* window, ImGuiViewportP* host_viewport);
 static bool             UpdateTryMergeWindowIntoHostViewports(ImGuiWindow* window);
-static void             SetCurrentViewport(ImGuiWindow* window, ImGuiViewportP* viewport);
 static bool             GetWindowAlwaysWantOwnViewport(ImGuiWindow* window);
 static int              FindPlatformMonitorForPos(const ImVec2& pos);
 static int              FindPlatformMonitorForRect(const ImRect& r);

imgui_internal.h

@@ -2462,6 +2462,7 @@ namespace ImGui
     IMGUI_API void                  TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& old_pos, const ImVec2& new_pos);
     IMGUI_API void                  ScaleWindowsInViewport(ImGuiViewportP* viewport, float scale);
     IMGUI_API void                  DestroyPlatformWindow(ImGuiViewportP* viewport);
+    IMGUI_API void                  SetCurrentViewport(ImGuiWindow* window, ImGuiViewportP* viewport);
     const ImGuiPlatformMonitor*     GetViewportPlatformMonitor(ImGuiViewport* viewport);
 
     // Settings

imgui_widgets.cpp

@@ -6625,12 +6625,15 @@ bool ImGui::BeginMainMenuBar()
     if (menu_bar_window == NULL || menu_bar_window->BeginCount == 0)
     {
         // Set window position
-        // We don't attempt to calculate our height ahead, as it depends on the per-viewport font size.
-        // However menu-bar will affect the minimum window size so we'll get the right height.
+        SetCurrentViewport(NULL, viewport);
+        float height = GetFrameHeight();
         ImVec2 menu_bar_pos = viewport->Pos + viewport->CurrWorkOffsetMin;
-        ImVec2 menu_bar_size = ImVec2(viewport->Size.x - viewport->CurrWorkOffsetMin.x + viewport->CurrWorkOffsetMax.x, 1.0f);
+        ImVec2 menu_bar_size = ImVec2(viewport->Size.x - viewport->CurrWorkOffsetMin.x + viewport->CurrWorkOffsetMax.x, height);
         SetNextWindowPos(menu_bar_pos);
         SetNextWindowSize(menu_bar_size);
+
+        // Report our size into work area
+        viewport->CurrWorkOffsetMin.y += height;
     }
 
     // Create window
@@ -6641,11 +6644,6 @@ bool ImGui::BeginMainMenuBar()
     bool is_open = Begin("##MainMenuBar", NULL, window_flags) && BeginMenuBar();
     PopStyleVar(2);
 
-    // Report our size into work area (for next frame) using actual window size
-    menu_bar_window = GetCurrentWindow();
-    if (menu_bar_window->BeginCount == 1)
-        viewport->CurrWorkOffsetMin.y += menu_bar_window->Size.y;
-
     g.NextWindowData.MenuBarOffsetMinVal = ImVec2(0.0f, 0.0f);
     if (!is_open)
     {