Implement GetOptimalSize for scrollbars

Change-Id: I4f0f8fd1e103a2433c38b6c0d9148d34d3df2083

vcl/inc/vcl/scrbar.hxx

@@ -147,6 +147,8 @@ public:
     const Link&     GetScrollHdl() const { return maScrollHdl;    }
     void            SetEndScrollHdl( const Link& rLink ) { maEndScrollHdl = rLink; }
     const Link&     GetEndScrollHdl() const { return maEndScrollHdl; }
+
+    virtual Size    GetOptimalSize(WindowSizeType eType) const;
 };
 
 // ----------------

vcl/source/control/scrbar.cxx

@@ -332,6 +332,8 @@ void ScrollBar::ImplCalc( sal_Bool bUpdate )
     Rectangle& maTrackRect = mpData->maTrackRect;  // TODO: remove when maTrackRect is no longer in mpData
     if ( mbCalcSize )
     {
+        Size aOldSize = GetOptimalSize(WINDOWSIZE_PREFERRED);
+
         const Rectangle aControlRegion( Point(0,0), aSize );
         Rectangle aBtn1Region, aBtn2Region, aTrackRegion, aBoundingRegion;
 
@@ -422,6 +424,12 @@ void ScrollBar::ImplCalc( sal_Bool bUpdate )
             maThumbRect.SetEmpty();
 
         mbCalcSize = sal_False;
+
+        Size aNewSize = GetOptimalSize(WINDOWSIZE_PREFERRED);
+        if (aOldSize != aNewSize)
+        {
+            queue_resize();
+        }
     }
 
     if ( mnThumbPixRange )
@@ -1500,6 +1508,17 @@ void ScrollBar::SetVisibleSize( long nNewSize )
     }
 }
 
+Size ScrollBar::GetOptimalSize(WindowSizeType) const
+{
+    Rectangle aCtrlRegion;
+    aCtrlRegion.Union(maBtn1Rect);
+    aCtrlRegion.Union(maBtn2Rect);
+    aCtrlRegion.Union(maPage1Rect);
+    aCtrlRegion.Union(maPage2Rect);
+    aCtrlRegion.Union(maThumbRect);
+    return aCtrlRegion.GetSize();
+}
+
 // =======================================================================
 
 void ScrollBarBox::ImplInit( Window* pParent, WinBits nStyle )