Not always using subpixel rendering / LCD font smoothing on OS X
Reported by
t...@close.io,
May 10 2016
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Issue descriptionUserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/601.5.17 (KHTML, like Gecko) Version/9.1 Safari/601.5.17 Steps to reproduce the problem: 1. Make sure "Use LCD font smoothing when available" is checked in System Preferences > General. 2. Open any website containing text on a OS X Retina screen. 3. If you zoom in / take a screenshot, you'll notice that subpixel anti-aliasing is not applied, i.e. the font smoothing is greyscale. 4. Also, if you open a website on a non-Retina screen, font smoothing is fine until it is moved to a Retina screen, where it disappears. Moving that same window back to the non-Retina screen doesn't restore subpixel smoothing, and fonts appear blurry. What is the expected behavior? Subpixel font rendering / LCD font smoothing should always be used if the OS X system setting is checked, just like in Safari. What went wrong? Subpixel font smoothing is disabled on Retina screens (it shouldn't). Did this work before? No Chrome version: 51.0.2704.36 Channel: n/a OS Version: OS X 10.11.4 Flash Version:
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May 13 2016
The first screenshot shows Google Chrome running on a Retina MacBook Pro with LCD font smoothing enabled. The second screenshot shows the URL bar zoomed in (from the first screenshot), where subpixel font smoothing is working properly (you can see this by the colorful anti-aliasing). The third screenshot shows content zoomed in (from the first screenshot), where subpixel font smoothing is not working (it's using greyscale anti-aliasing). This happens not just on the About page, but on all websites. I can record a screencast later in case you can't reproduce 4), but the attached screenshots should already demonstrate that there is an issue.
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May 14 2016
Thank you for providing more feedback. Adding requester "spqchan@chromium.org" for another review and adding "Needs-Review" label for tracking. For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot
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May 17 2016
I noticed this too, but on linux. A test page is: http://www.ilfattoquotidiano.it
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May 17 2016
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Jun 15 2016
[mac triage] chrome://help/ has layers (e.g., similar to chrome://settings/, scrolling causes the content to go underneath fixed-position stuff at the top of the page). I think we deliberately disable subpixel AA for some situations on retina devices only, since it gets computationally expensive to preserve it when layers get involved. assigning to someone who may know more. Possibly related to Issue 381840
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Jun 15 2016
On high-DPI screens, like retina, we deliberately disable sub-pixel font rendering in favor of improved scrolling performance. Specifically, the "--enable-prefer-compositing-to-lcd-text" flag is always true. On linux there are probably cases where we disable lcd text but I am not expert on this. Assigning to someone who knows even more and is currently working on related issues. There may be a bug here if we do not revert back to sub-pixel text when the monitor changes and we have information that would let us do so.
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Nov 22 2016
Yes, that is correct. This issue has been reported for linux previously as issue 583273 and we have talked about what the threshold should be on issue 242643 . See https://cs.chromium.org/chromium/src/content/renderer/render_view_impl.cc?dr=CSs&q=DeviceScaleEnsuresTextQuality&sq=package:chromium&l=334 for whether we are willing to promote elements into composited layers even if they will lose LCD text and https://cs.chromium.org/chromium/src/content/renderer/render_view_impl.cc?dr=CSs&q=DeviceScaleEnsuresTextQuality&sq=package:chromium&l=334 for whether LCD text rendering is enabled. You might be able to enable LCD Text antialiasing in chrome://flags/#lcd-text-aa to force this to prefer anti-aliasing to compositing but keep in mind this will result in less responsive scrolling due to needing to repaint. |
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Comment 1 by spqc...@chromium.org
, May 13 2016Labels: Needs-Feedback