Negative left side bearing in GPOS (net zero lsb) leads to bounding box overflow |
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Issue descriptionWhat steps will reproduce the problem? (1) Open test-20170320-simple.html with font SidebearingsG1-Regular.ttf in the same folder, which activates the ss05 feature, which moves the left side bearing of the H 90 units to the left, and reduces the advance width by 180 units. The afkdo feature file for the font looks like this when ss05 is active: pos H <-90 0 -180 0>; (2) Observe highlighted bounding box when click in the "Henry..." paragraph (3) Zoom in, magnify left stem of H What is the expected result? Left stem of H should not protrude outside the bounding box. What happens instead? Left stem of H protrudes slightly left outside the bounding box. $ hb-shape --features="ss05=1" SidebearingsG1-Regular.ttf "Henry" [H=0@-90,0+472|e=1+496|n=2+547|r=3+366|y=4+467] Behdad, what's the @-90 in terms of hb_buffer_t info? Would we need to do something like a shifting operation on all the subsequent advance coordinates? Would that be Blink's job in your opinion, or could we set HarfBuzz to a mode where all advance coordinates get normalized to be 0 based?
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Apr 19 2017
HarfBuzz output looks correct. > Behdad, what's the @-90 in terms of hb_buffer_t info? That's x_offset. > Would we need to do something like a shifting operation on all the subsequent advance coordinates? No. That's what the -180 adjustment to x_advance is for. I don't think there's a problem here. The border you see is drawn because of contenteditable, and it has no room, so it draws one/two pixel on each side of the box. No wonder it overlaps with content! Just remove contenteditable and add proper border and you see there's no problem.
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May 22 2017
Dominik, can you check this out again? I think it's a non-issue.
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May 25 2017
The border is because of contenteditable, but the position of the H is not affected if the divs are not contenteditable. See attached HTML and PNG.
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May 25 2017
In other words, contenteditable does not affect positioning of the H. When you say "add proper border" what do you mean?
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May 25 2018
This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue. Sorry for the inconvenience if the bug really should have been left as Available. For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot
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May 29 2018
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May 30 2018
Dominik? |
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Comment 1 by drott@chromium.org
, Mar 21 2017