Investigate scrolling perf vs. ClearType at DSF>1 when chrome://flags#enable-use-zoom-for-dsf is on |
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Issue descriptionAt the moment, with chrome://flags#enable-use-zoom-for-dsf OFF we use greyscale AA, and with it on, we use ClearType AA (in the content area). It looks nicer for 1 <= DSF < 2, but it might not be worth the battery/scroll perf. I think we had to disable ClearType at DSF>1 for scrolling perf (otherwise it causes a lot more painting).
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Jun 30 2016
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Jul 13 2016
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Jul 18 2016
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Jul 18 2016
We disable sub-pixel text and instead composite scrolling layers for DSF > 1, the check of which is probably broken now that zoom is used. So now we're no longer compositing when we could and scrolling performance will suffer. We should see performance test breakage. I feel pretty strongly that in the short term we should replicate the current behavior. For clarification, is this bug only referring to the 1 <= DSF < 2 range, or is the DSF = 2 case also changed?
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Jul 18 2016
I'm not very familiar with the code you're referring to but anything that's directly asking for the device scaling factor is probably unchanged. This is turned on by default on Canary right now and I haven't seen any performance test failures yet.
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Jul 18 2016
I got some more context on the problem and it shouldn't be too hard to just re-enable the code path that selects greyscale AA at higher DSFs, so I'll do that.
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Jul 18 2016
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Jul 19 2016
Unless I'm mistaken the code in question is DeviceScaleEnsuresTextQuality in render_view_impl.cc. This is unchanged and still working just fine. The OP made it sound like it's broken with use-zoom-for-dsf on, but that flag mostly touches Blink so it seems unlikely to me. I did debug into it just in case and it's still receiving the correct scale factor. It's possible we should enable this for 1.25 DSF too, but that's a separate problem. |
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Comment 1 by scottmg@chromium.org
, Jun 23 2016