tdf#113714 vcl menu bar window: avoid flicker

Regression from commit 458a827e96523ac52d021f1fd3653b5a734940c0 (further
refactor Menu to use RenderContext, 2015-05-15), if we do full paint
instead of incremental paint, then need to ensure that an intermediate
state is not painted.

Paint happens at idle time by default on Windows (OpenGL) and also on
Linux (gtk3), but some other backends like Windows GDI had flicker, this
fixes the problem.

(cherry picked from commit e8d5b8beb5958147235ff955ed38c47b51d860ff)

Change-Id: I530166cea93513aec4648dd0a385359f4b998b6f
Reviewed-on: https://gerrit.libreoffice.org/72673
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>

1 files changed, 22 insertions, 14 deletions

diff --git a/vcl/source/window/menubarwindow.cxx b/vcl/source/window/menubarwindow.cxx
index 25ab264bc9d9..66444c082153 100644
--- a/vcl/source/window/menubarwindow.cxx
+++ b/vcl/source/window/menubarwindow.cxx
@@ -24,6 +24,7 @@
 #include <vcl/dockingarea.hxx>
 #include <vcl/settings.hxx>
 #include <vcl/taskpanelist.hxx>
+#include <vcl/virdev.hxx>
 #include <sal/log.hxx>
 
 #include <salframe.hxx>
@@ -916,47 +917,54 @@ void MenuBarWindow::Paint(vcl::RenderContext& rRenderContext, const tools::Recta
         return;
     }
 
+    // Make sure that all actual rendering happens in one go to avoid flicker.
+    ScopedVclPtrInstance<VirtualDevice> pBuffer;
+    pBuffer->SetOutputSizePixel(aOutputSize, false);
+
     if (rRenderContext.IsNativeControlSupported(ControlType::Menubar, ControlPart::Entire))
     {
         MenubarValue aMenubarValue;
         aMenubarValue.maTopDockingAreaHeight = ImplGetTopDockingAreaHeight(this);
 
         if (!rStyleSettings.GetPersonaHeader().IsEmpty())
-            Erase(rRenderContext);
+            Erase(*pBuffer);
         else
         {
             tools::Rectangle aCtrlRegion( Point(), aOutputSize );
 
-            rRenderContext.DrawNativeControl(ControlType::Menubar, ControlPart::Entire, aCtrlRegion,
-                                             ControlState::ENABLED, aMenubarValue, OUString());
+            pBuffer->DrawNativeControl(ControlType::Menubar, ControlPart::Entire, aCtrlRegion,
+                                       ControlState::ENABLED, aMenubarValue, OUString());
         }
 
-        ImplAddNWFSeparator(rRenderContext, aOutputSize, aMenubarValue);
+        ImplAddNWFSeparator(*pBuffer, aOutputSize, aMenubarValue);
     }
 
     // shrink the area of the buttons
     aOutputSize.AdjustWidth( -(aCloseBtn->GetSizePixel().Width()) );
 
-    rRenderContext.SetFillColor(rStyleSettings.GetMenuColor());
-    pMenu->ImplPaint(rRenderContext, aOutputSize, 0);
+    pBuffer->SetFillColor(rStyleSettings.GetMenuColor());
+    pMenu->ImplPaint(*pBuffer, aOutputSize, 0);
 
     if (nHighlightedItem != ITEMPOS_INVALID && pMenu && !pMenu->GetItemList()->GetDataFromPos(nHighlightedItem)->bHiddenOnGUI)
-        HighlightItem(rRenderContext, nHighlightedItem);
+        HighlightItem(*pBuffer, nHighlightedItem);
     else if (ImplGetSVData()->maNWFData.mbRolloverMenubar && nRolloveredItem != ITEMPOS_INVALID)
-        HighlightItem(rRenderContext, nRolloveredItem);
+        HighlightItem(*pBuffer, nRolloveredItem);
 
     // in high contrast mode draw a separating line on the lower edge
     if (!rRenderContext.IsNativeControlSupported( ControlType::Menubar, ControlPart::Entire) &&
         rStyleSettings.GetHighContrastMode())
     {
-        rRenderContext.Push(PushFlags::LINECOLOR | PushFlags::MAPMODE);
-        rRenderContext.SetLineColor(COL_WHITE);
-        rRenderContext.SetMapMode(MapMode(MapUnit::MapPixel));
+        pBuffer->Push(PushFlags::LINECOLOR | PushFlags::MAPMODE);
+        pBuffer->SetLineColor(COL_WHITE);
+        pBuffer->SetMapMode(MapMode(MapUnit::MapPixel));
         Size aSize = GetSizePixel();
-        rRenderContext.DrawLine(Point(0, aSize.Height() - 1),
-                                Point(aSize.Width() - 1, aSize.Height() - 1));
-        rRenderContext.Pop();
+        pBuffer->DrawLine(Point(0, aSize.Height() - 1),
+                          Point(aSize.Width() - 1, aSize.Height() - 1));
+        pBuffer->Pop();
     }
+
+    rRenderContext.DrawOutDev(Point(0, 0), GetOutputSizePixel(), Point(0, 0), GetOutputSizePixel(),
+                              *pBuffer);
 }
 
 void MenuBarWindow::Resize()