While working on issue 87689 I noticed that some old parts of GSL code spend a lot of energy to emulate 
common graphics operations, e.g. by using the XOR trick to emulate polygon shaped clipping of gradient 
areas.

That emulation layer was certainly useful for primitive graphics targets, but on a powerful graphics system 
like Quartz it does more harm than good. It should be disabled. In the example of the XOR trick I 
mentioned above that can be perfectly replaced by using Quartz's polygon clipping support.

Unfortunately we'll still need a different kind of emulation to handle legacy documents. E.g. old metafiles 
sometimes need XOR, but Quartz doesn't support this obsolete blend mode.