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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [GTK][Threaded Compositor] Several flaky tests due to differences in scrollbars"
href="https://bugs.webkit.org/show_bug.cgi?id=160450">160450</a>
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<th>Summary</th>
<td>[GTK][Threaded Compositor] Several flaky tests due to differences in scrollbars
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<th>Classification</th>
<td>Unclassified
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<th>Product</th>
<td>WebKit
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<th>Version</th>
<td>WebKit Local Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
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<th>Status</th>
<td>NEW
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<th>Keywords</th>
<td>Gtk, LayoutTestFailure
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>WebKit Gtk
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>cgarcia@igalia.com
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<th>CC</th>
<td>bugs-noreply@webkitgtk.org, yoon@igalia.com, zan@falconsigh.net
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<pre>We still have a lot of flaky tests since we switched to the threaded compositor. I can't reproduce them though. I've seen several reftests failing because there's a part of the vertical scrollbar that is not rendered. It turns out that the part not rendered is the second tile of the scrollbar layer, that for some reason it seems to be rendered later. So, my guess is that we force a repaint that when finishes hasn't actually painted all the tiles. Then the UI process takes the screenshot too early, before the second tile of the scrollbar layer is actually painted. I took advantage of the DRI3 bug, to see how things happen when everything is slow, and that's exactly what happens, everything is rendered in one pass and then the second tile of the scrollbar layer. See:
<a href="http://people.igalia.com/cgarcia/webkitgtk-scrollbar-layer.mp4">http://people.igalia.com/cgarcia/webkitgtk-scrollbar-layer.mp4</a>
I'm not sure how to fix it, because I don't know why that happens and I can't really reproduce the flakiness, but we could try to wait for more damage events in the UI process before taking the screenshot.</pre>
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