Merge parallel horizontal edges in ImagingDrawPolygon #5347
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Resolves #5235. Alternative to #5240
The issue reports missing pixels if a polygon is drawn with multiple horizontal lines in sequence, decreasing in x. This problem arises because, well,
draw_horizontal_linesfrom #5183 loops through edges in order, working from left to right.This PR adds a solution in
ImagingDrawPolygon- is the next edge to be added a horizontal line in the same direction as the last edge? If so, don't bother adding another edge, just extend the last one.Only the 'decreasing in x' case is necessary to fix the problem. However, since we're there, let's merge 'increasing in x' lines as well, to save a bit of memory.