Detect if polypolygon is a rectangle in DrawGradient

If the polypolygon that we use for DrawGradient is a rectangle, then we
need to 1) expand the gradient rectangle to avoid missing lines on the
right and bottom edge, and 2) we should pass NULL as the clipping
parameter for ImplDrawLinearGradient and ImplDrawComplexGradient.

Change-Id: I8d8289ace069b5c500db59d1a2addfcea8388dfb

vcl/source/gdi/outdev4.cxx

@@ -760,10 +760,22 @@ void OutputDevice::ClipAndDrawGradient ( Gradient &rGradient, const PolyPolygon
                 if ( !rGradient.GetSteps() )
                     rGradient.SetSteps( GRADIENT_DEFAULT_STEPCOUNT );
 
+                if ( rPolyPoly.IsRect() )
+                {
+                    // because we draw with no border line, we have to expand gradient
+                    // rect to avoid missing lines on the right and bottom edge
+                    aRect.Left()--;
+                    aRect.Top()--;
+                    aRect.Right()++;
+                    aRect.Bottom()++;
+                }
+
+                // if the clipping polypolygon is a rectangle, then it's the same size as the bounding of the
+                // polypolygon, so pass in a NULL for the clipping parameter
                 if( rGradient.GetStyle() == GradientStyle_LINEAR || rGradient.GetStyle() == GradientStyle_AXIAL )
-                    ImplDrawLinearGradient( aRect, rGradient, false, &aClipPolyPoly );
+                    ImplDrawLinearGradient( aRect, rGradient, false, aClipPolyPoly.IsRect() ? NULL : &aClipPolyPoly );
                 else
-                    ImplDrawComplexGradient( aRect, rGradient, false, &aClipPolyPoly );
+                    ImplDrawComplexGradient( aRect, rGradient, false, aClipPolyPoly.IsRect() ? NULL : &aClipPolyPoly );
             }
 
             Pop();