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Remove spikes when drawing thin pieslices #5460

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merged 2 commits into from May 14, 2021
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xtsm
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@xtsm xtsm commented May 2, 2021

Fixes #5432 .

@radarhere radarhere changed the title Remove spikes when drawing thin pies Remove spikes when drawing acute pieslices May 5, 2021
@radarhere radarhere changed the title Remove spikes when drawing acute pieslices Remove spikes when drawing thin pieslices May 5, 2021
Comment on lines +1362 to +1363
spike_clipper->a = (xl + xr) / 2.0;
spike_clipper->b = (yl + yr) / 2.0;
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Here's my explanation of what is happening here.
This is taking the average of the two points on the outside of the circle. Going through the center of the circle as well, that gives us a line down the middle of the pieslice.
Then by swapping x and y (normally y would be with a), and multiplying one of them by -1, it gives us a perpendicular line. Because the line also goes through the center of the circle, that cuts off the spike.

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yeah, that's one way to put it
line equation Ax+By+C=0 can be also written as rn + C = 0, r(x, y), n(A, B) - i.e. n(A, B) is a normal vector for line

@radarhere radarhere merged commit 78406ed into python-pillow:master May 14, 2021
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pieslice draws very thin sectors incorrectly
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