fdo#74702 Refactor gradient clipping functions

There are two gradient clipping functions: one uses a normal intersection
to get the symmetric difference to clip the gradient - this is used by
OS X and when printing. The other uses XOR clipping, which is an elegant
trick to implement complex clipping on graphics systems that have minimal
capabilities.
cf. http://www.openoffice.org/marketing/ooocon2008/programme/wednesday_1401.pdf

Change-Id: Iab16258c8e758c41a29337525927ba780329e887
Reviewed-on: https://gerrit.libreoffice.org/8873Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>

include/vcl/outdev.hxx

@@ -844,6 +844,12 @@ protected:
     virtual void                EmulateDrawTransparent( const PolyPolygon& rPolyPoly, sal_uInt16 nTransparencePercent );
     void                        DrawInvisiblePolygon( const PolyPolygon& rPolyPoly );
 
+    virtual void                ClipGradientToBounds( Gradient &rGradient, const PolyPolygon &rPolyPoly );
+    void                        ClipGradient( Gradient &rGradient, const PolyPolygon &rPolyPoly, const Rectangle &rBoundRect );
+    void                        XORClipGradient( Gradient &rGradient, const PolyPolygon &rPolyPoly, const Rectangle &rBoundRect );
+
+    virtual void                ClipGradientMetafile ( const Gradient &rGradient, const PolyPolygon &rPolyPoly, const Rectangle &rBoundRect );
+
 private:
     typedef void ( OutputDevice::* FontUpdateHandler_t )( bool );
 

include/vcl/print.hxx

@@ -274,7 +274,10 @@ public:
 
 protected:
     long                        ImplGetGradientStepCount( long nMinRect ) SAL_OVERRIDE;
+    virtual void                ClipGradientToBounds( Gradient &rGradient, const PolyPolygon &rPolyPoly ) SAL_OVERRIDE;
+    virtual void                ClipGradientMetafile ( const Gradient &rGradient, const PolyPolygon &rPolyPoly, const Rectangle &rBoundRect ) SAL_OVERRIDE;
     virtual bool                UsePolyPolygonForComplexGradient() SAL_OVERRIDE;
+
     void                        ScaleBitmap ( Bitmap&, SalTwoRect& ) SAL_OVERRIDE { };
 
 public:

vcl/source/gdi/print.cxx

@@ -1812,4 +1812,19 @@ bool Printer::UsePolyPolygonForComplexGradient()
     return true;
 }
 
+void Printer::ClipGradientToBounds ( Gradient &rGradient, const PolyPolygon &rPolyPoly )
+{
+    const Rectangle aBoundRect( rPolyPoly.GetBoundRect() );
+
+    ClipGradient ( rGradient, rPolyPoly, aBoundRect );
+}
+
+void Printer::ClipGradientMetafile ( const Gradient &rGradient, const PolyPolygon &rPolyPoly, const Rectangle &rBoundRect )
+{
+    Push( PUSH_CLIPREGION );
+    IntersectClipRegion(Region(rPolyPoly));
+    DrawGradient( rBoundRect, rGradient );
+    Pop();
+}
+
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */