tdf#95648: Erase the OpenGLCompatibleDC to white before drawing text into it

For some reason this is needed in the case of GraphiteWinLayout and
OpenGL. Otherwise when a space glyph is "drawn" into a space that is
wider than the nominal width of the space glyph, we get two black
rectangles surrounding the white space "glyph".

Change-Id: Ifb4ea00d9e5f078518ac97d7dd18694088aa1cdf

vcl/win/gdi/winlayout.cxx

@@ -566,7 +566,7 @@ void WinLayout::DrawText(SalGraphics& rGraphics) const
     if (!mbUseOpenGL)
     {
         // no OpenGL, just classic rendering
-        DrawTextImpl(hDC);
+        DrawTextImpl(hDC, NULL);
     }
     else if (CacheGlyphs(rGraphics) &&
              DrawCachedGlyphs(rGraphics))
@@ -623,7 +623,7 @@ void WinLayout::DrawText(SalGraphics& rGraphics) const
         SetTextAlign(aDC.getCompatibleHDC(), nTextAlign);
 
         // the actual drawing
-        DrawTextImpl(aDC.getCompatibleHDC());
+        DrawTextImpl(aDC.getCompatibleHDC(), &aRect);
 
         COLORREF color = GetTextColor(hDC);
         SalColor salColor = MAKE_SALCOLOR(GetRValue(color), GetGValue(color), GetBValue(color));
@@ -1764,7 +1764,7 @@ void UniscribeLayout::Simplify( bool /*bIsBase*/ )
     }
 }
 
-void UniscribeLayout::DrawTextImpl(HDC hDC) const
+void UniscribeLayout::DrawTextImpl(HDC hDC, const Rectangle* /* pRectToErase */) const
 {
     HFONT hOrigFont = DisableFontScaling();
 
@@ -2801,8 +2801,14 @@ void  GraphiteWinLayout::AdjustLayout(ImplLayoutArgs& rArgs)
     maImpl.AdjustLayout(rArgs);
 }
 
-void GraphiteWinLayout::DrawTextImpl(HDC hDC) const
+void GraphiteWinLayout::DrawTextImpl(HDC hDC, const Rectangle* pRectToErase) const
 {
+    if (pRectToErase)
+    {
+        RECT aRect = { pRectToErase->Left(), pRectToErase->Top(), pRectToErase->Left()+pRectToErase->GetWidth(), pRectToErase->Top()+pRectToErase->GetHeight() };
+        FillRect(hDC, &aRect, static_cast<HBRUSH>(GetStockObject(WHITE_BRUSH)));
+    }
+
     HFONT hOrigFont = DisableFontScaling();
     maImpl.DrawBase() = WinLayout::maDrawBase;
     maImpl.DrawOffset() = WinLayout::maDrawOffset;

vcl/win/gdi/winlayout.hxx

@@ -53,7 +53,7 @@ public:
     virtual void        DrawText(SalGraphics&) const override;
 
     /// Draw to the provided HDC.
-    virtual void        DrawTextImpl(HDC hDC) const = 0;
+    virtual void        DrawTextImpl(HDC hDC, const Rectangle* pRectToErase) const = 0;
 
     virtual bool        CacheGlyphs(SalGraphics& rGraphics) const = 0;
     virtual bool        DrawCachedGlyphs(SalGraphics& rGraphics) const = 0;
@@ -75,7 +75,7 @@ public:
 
     virtual bool    LayoutText( ImplLayoutArgs& ) override;
     virtual void    AdjustLayout( ImplLayoutArgs& ) override;
-    virtual void    DrawTextImpl(HDC hDC) const override;
+    virtual void    DrawTextImpl(HDC hDC, const Rectangle* pRectToErase) const override;
     virtual bool    CacheGlyphs(SalGraphics& rGraphics) const override;
     virtual bool    DrawCachedGlyphs(SalGraphics& rGraphics) const override;
     virtual int     GetNextGlyphs( int nLen, sal_GlyphId* pGlyphs, Point& rPos, int&,
@@ -168,7 +168,7 @@ public:
     // used by upper layers
     virtual bool  LayoutText( ImplLayoutArgs& ) override;    // first step of layout
     virtual void  AdjustLayout( ImplLayoutArgs& ) override;  // adjusting after fallback etc.
-    virtual void  DrawTextImpl(HDC hDC) const override;
+    virtual void  DrawTextImpl(HDC hDC, const Rectangle* pRectToErase) const override;
     virtual bool  CacheGlyphs(SalGraphics& rGraphics) const override;
     virtual bool  DrawCachedGlyphs(SalGraphics& rGraphics) const override;