[Webkit-unassigned] [Bug 82646] New: Idle painting is not sufficient to pre-paint animated layers and delay animation start time

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=82646

           Summary: Idle painting is not sufficient to pre-paint animated
                    layers and delay animation start time
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: epenner at chromium.org
                CC: enne at google.com, nduca at chromium.org,
                    danakj at chromium.org, vollick at chromium.org


I wanted to see if it was possible to completely pre-paint animated layers, to avoid hiccups due to painting mid-animation. I found that even if I instructed idle-painting to pre-paint all animated layers entirely (basically making https://bugs.webkit.org/show_bug.cgi?id=82117 hyper aggressive), this painting would not occur on the first webkit commit of the animation (which is crucial because it delays animation start times).  However, if I did the painting in the main pass, it would indeed get painted on the first frame and never wait for unpainted tiles.

Maybe there is a way to solve this in the short term to make page transition animations smooth. My first thought is if we had the unclipped visible rect, we could expand it for animated layers until we hit some memory limit (eg. one viewport worth of tiles in addition to the visible part of the layer) and paint it in the main pass rather than the idle pass... Lots of other solutions are possible, like doing two paints in one commit maybe, but I'm less familiar with what we would need for that.

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