Another partial fix for fdo#45219

Make sure transparent polygons really only cover the polygonal area,
not the whole bounding box for sprites.

canvas/source/vcl/canvashelper.cxx

@@ -499,12 +499,11 @@ namespace vclcanvas
             }
 
             if( mp2ndOutDev )
-            {
-                if( !nTransparency || bSourceAlpha )
             {
                 // HACK. Normally, CanvasHelper does not care
                 // about actually what mp2ndOutDev is...
-                    if( bSourceAlpha && nTransparency == 255 )
+                // well, here we do & assume a 1bpp target.
+                if( nTransparency > 127 )
                 {
                     mp2ndOutDev->getOutDev().SetDrawMode( DRAWMODE_WHITELINE | DRAWMODE_WHITEFILL | DRAWMODE_WHITETEXT |
                                                           DRAWMODE_WHITEGRADIENT | DRAWMODE_WHITEBITMAP );
@@ -518,11 +517,6 @@ namespace vclcanvas
                     mp2ndOutDev->getOutDev().DrawPolyPolygon( aPolyPoly );
                 }
             }
-                else
-                {
-                    mp2ndOutDev->getOutDev().DrawTransparent( aPolyPoly, (sal_uInt16)nTransPercent );
-                }
-            }
         }
 
         // TODO(P1): Provide caching here.