从多边形中构建“内冲程”效果。

I'm drawing a whole bunch of Polygons onto a canvas, most of which share an edge with at least one other Polygon. I'd like to indicate a Polygon is "special" by outlining it, however due to the overlapping edges the Stroke on a Polygon tends to be partially drawn over by another Polygon causing the Stroke to look thinner than it should in places. Additionally, depending on draw order, a Polygon may have its Stroke almost entirely covered by those around it. Spacing the Polygons out is not a very attractive option, as visible gaps between Polygons are much less preferable to this "thin stroke" problem. onto a ca