Eliminate transition effects from thumbnail loader #6026
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During A/B testing we found a significant preference (increased engagement time, reduced downloads of original PDF for local viewing) for the version that doesn't animate loading thumbnails. Profiling shows that the transition effects hit at a pessimal time when the compositor is busy rendering the main PDF page view, and rendering thumbnail previews, causing the main scroll view to stutter. With the transition removed scrolling is perceptibly smoother in Chrome and Firefox. We also hypothesize that the transition effects added to a perception of slowness but presumably the aforementioned stutter is the primary issue here.
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Do you have a PDF where the effect is clearly visible according to you? I also don't see the use of the transition effects, but having them removed I don't notice any change in scrolling behavior either. Perhaps it's not clearly visible with the Tracemonkey paper. |
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I tend to agree with the change, scrolling documents goes down below 30 fps often, which means that this transition usually is active for only 2-3 frames. which is hard different from turn on and off. so there is unnecessary work for the browser to render which you won't see. |
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The UI stutter happens when scrolling through more complex PDFs (containing scaled graphics etc.) so won't be exhibited by the Tracemonkey document. I can dig up an example when I'm back in the office Monday but scrolling fast through any graphics-heavy PDF should highlight the issue. We initially thought the slowdown was due to our Retina patch from #6025 (where the stutter is more pronounced) but it turned out the culprit was the thumbnail transition. |
Eliminate transition effects from thumbnail loader
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thanks @mcorb |
During A/B testing we found a significant preference (increased engagement
time, reduced downloads of original PDF for local viewing) for the version that
doesn't animate loading thumbnails.
Profiling shows that the transition effects hit at a pessimal time when the
compositor is busy rendering the main PDF page view, and rendering thumbnail
previews, causing the main scroll view to stutter. With the transition removed
scrolling is perceptibly smoother in Chrome and Firefox. We also hypothesize
that the transition effects added to a perception of slowness but presumably
the aforementioned stutter is the primary issue here.