1460480 - tweetdeck shows poor retained-dl behaviour

Status: NEW

(Core :: Web Painting, enhancement, P3)

Description

[Matt Woodrow (:mattwoodrow)]

Enable layout.display-list.show-rebuild-area=true, and mouse-over various things on tweetdeck.twitter.com (logged in).

Quite often we see the whole screen flash in blue, which suggests that we're building display items for an area much larger than what actually changed (hopefully just the icon under the mouse).

It would be good to investigate this and see if we can build less.

Enabling the PrintDisplayList calls in RetainedDisplayListBuilder::AttemptPartialUpdate will show the partial list we build, and enabling CRR_DEBUG will log which frames were modified and the rebuild area we computed from that.

Identifying the paint where we built a large area, and then figuring out which frame contributed the area would be a good start.

Dumping the frame tree (nsIFrame::DumpFrameTree) is useful, as is rr (to rewind back to the callstack that modified the offending frame - nsIFrame::MarkNeedsDisplayItemRebuild).