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Clip small linewidths in agg#14560
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src/_backend_agg.h Outdated
| // Too small linewidths are clipped because they require a lot of | ||
| // computation and do not make sense even with antialiasing. | ||
| // Compare github #14498. | ||
| linewidth = (linewidth < 0.01) ? 0.01 : mpl_round(linewidth); |
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I guess clipping at 1/256 would make sense because the quantization of the channels is 8bit so linewidths<1/256 (or half that? perhaps...) would be quantized to zero.
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What are channels in this context? I only know color channels but don't see how that could be related to linewidth.
Anyways, 0.01 causes some image comparison failures, trying 0.001 to see if that fixes it.
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I meant color channels.
With antialiasing, linewidths<1 are basically represented by setting the color channels to (linewidthreal_color) (blending with the background), but that's then quantized to 8 bits so linewidths<1/(2256) should result in nothing being drawn.
timhoffm commentedJun 17, 2019 • edited
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Still 44 image comparison failures for a cutoff at 0.001. Needs to be investigated, ... later. |
Possibly clip small linewidths to zero (i.e. don't draw them at all) instead of 0.001? just a random idea... |
Try forcing linewidth < 0.001 to 0. |
timhoffm commentedJul 7, 2019 • edited
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Interestingly, forcing linewidth < 0.001 to 0 causes a lot of image comparison failures with dashed lines having slightly modified widths. |
Anybody can pick this up if wanted. I don't have the time to debug this for now. |
PR Summary
Fixes#14498. See there for a full discussion.
Note: I've noticed that the following code uses a mixture of
gc.linewidth(the original value) andlinewidth(the clipped value). Can somebody with more Agg knowledge please check if that is correct?