Bug 132486 – Web Inspector: horizontally scrolling the timelines overview is slower as range selection grows

• Component: Web Inspector
• Status: NEW

[Brian Burg]

It appears that we don't layerize the overview, so the entire normal tile has to be repainted.

[Radar WebKit Bug Importer]

<rdar://problem/16799043>

[Brian Burg]

Created attachment 230691 [details]
tile repaint counts - should show compositing layer

[Brian Burg]

Also noticeably slower when the scrollbar overlay shows up (scroll with window focused) vs not (scroll when window inactive).

I would prefer to ditch the scrollbar and paint our own ticker that shows the entire range and the currently visible subrange, if zoomed beyond 1x/showing everything.

[Simon Fraser (smfr)]

We don't have any kind of accelerated overflow:scroll on OS X.

[Timothy Hatcher]

Some of the slowness could be coming from our handling of scroll events (which are async) to update the rendered area of the overview graphs.

[Blaze Burg]

STEPS TO REPRODUCE:

 * Go to CNN.com
 * Open Inspector
 * Force-reload
 * Wait for auto-recording to stop (20s)
 * Open timelines panel
 * Zoom in on timelines overview (using wheel / trackpad)
 * scroll horizontally with wheel, trackpad, or dragging scrollbar
 * select a small range of the timeline, and scroll horizontally again

EXPECTED:

 * horizontal scrolling speed shouldn't be affected by the size of the selection range.

ACTUAL:

 * as the selection becomes wider, horizontal scrolling has worse performance.


NOTES:
 * Maybe we are doing work we shouldn't be doing- that's O(records in range) - when the view range changes.

[Timothy Hatcher]

It could be the code in TimelineRecordBar.createCombinedBars, which has a comment:

// FIXME: Do a binary search for records that fall inside start and current time.