STR: 1. Load https://upload.wikimedia.org/wikipedia/commons/f/f8/Whisky_distilleries_and_regions_in_Scotland.svg 2. Scroll around the document. (It's probably larger than your viewport.) ACTUAL RESULTS: Scrolling is janky. For comparison: in Chrome 46, it's pretty smooth. I'm using Firefox Nightly 43.0a1 (2015-08-23)
(In reply to Daniel Holbert [:dholbert] (vacation 8/27-9/13) from comment #0) > 2. Scroll around the document. (It's probably larger than your viewport.) Specifically: Click & drag the scrollbar up & down rapidly. There's a noticeable repaint lag in Firefox, vs. not in Chrome. (I'm using Firefox with e10s enabled, on Linux, BTW. Turning on layers acceleration doesn't seem to help (via layers.acceleration.force-enabled))
Daniel, you previously said that paint flashing wasn't showing over-invalidation for you, but when I scroll (using taps of the arrow keys) every third or so change in scroll position results in an invalidation of almost the entire window (when that doesn't happen, scrolling doesn't seem to take too long compared to Chrome). This is on OS X. (I also did a quick profile and most time is being spent under DrawTargetCG::Stroke. Not much point digging into that further though until any over-invalidation is sorted out.)
Created attachment 8651818 [details] screenshot w/ paint flashing after scrolling down slowly with mousewheel Hmm, I think you're right. Most of my careful scrolling (with mousewheel) results in small strips of painting, but occasionally a large portion of the screen gets repainted all at once. Here's a screenshot showing that -- small strips (good), plus one large squarish recent paint. I think you're right that the jank all seems to come when we do these large paint operations.
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