Comment 7 for bug 1744989

Sorry for the delay in responding. Finally had a chance to check if the issue is still occurring in the nightly build.

For sake of completeness, I tested with all four antialiasing options.

CAIRO_ANTIALIAS_NONE: As you suspected, turning off antialiasing removed these artifacts.

CAIRO_ANTIALIAS_GOOD/CAIRO_ANTIALIAS_BEST: There was no perceptible difference between the artifacts introduced between the Good and Best antialiasing, with both options creating identical images when post-processed to remove transparency and compared via diff tool.

CAIRO_ANTIALIAS_FAST: Fast produced significantly fewer artifacts than GOOD/BEST, which would be expected if antialiasing is the culprit, as fast is presumably doing less antialiasing to produce a faster result.