Use faster bbox-specialised clipping algorithm #482
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Impressive performance wins! Happy to see that code being useful :) |
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Huge thanks for the original - it's not often that one encounters such a dramatic performance boost! Plus of course we benefit from @kleunen's magical geometry-correction code which neatly removes the edge artefacts from Sutherland-Hodgman. |
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When writing tiles, we spend a lot of time in
boost::geometry::intersection. This is an all-purpose polygon intersection routine. Our needs are more specialised: we just want to clip polygons to a rectangular bounding box.This PR replaces the call to
boost::geometry::intersectionwith a simpler and (hopefully) faster clipping routine - the Sutherland-Hodgman algorithm, ported from https://github.com/mapbox/lineclip.Comparative timings:
File size is similar and as yet I haven't spotted any rendering artefacts.