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Issue metadata

Status: WontFix
Owner: ----
Closed: Nov 2016
Cc:
Components:
EstimatedDays: ----
NextAction: ----
OS: Windows
Pri: 2
Type: Bug



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Slow paint on scroll for absolute positioned elements

Reported by insensi...@gmail.com, Nov 10 2016

Issue description

UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.87 Safari/537.36

Steps to reproduce the problem:
1. Visit https://jsfiddle.net/docjom96/
2. Click 'Static' button and wait until button goes to normal state
3. Start timeline recording in Chrome Developer Tools
4. Scroll to top/bottom several times area with rectangles using scroll bar
5. Stop timeline recording
6. Notice average paint time (green rectangles) in timeline
7. Repeat the same for 'Absolute' button
8. Compare paint timings

What is the expected behavior?
Paint timings are the same when scrolling absolute positioned elements

What went wrong?
Using absolute positioning increases paint time when scrolling although exactly the same rectangle with same graphics needs to be painted.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 54.0.2840.87  Channel: n/a
OS Version: 10.0
Flash Version: Shockwave Flash 23.0 r0

I also attached two screenshots made on my machine using above fiddle.
 
static.png
29.8 KB View Download
absolute.png
25.8 KB View Download
Status: WontFix (was: Unconfirmed)
The final painted content is the same, but the techniques used to paint static vs absolute position content will vary. That can easily account for the different paint times you are seeing.

For future reference, starting in M56 you can put a solid background color on that scrolling container and there will be no repainting at all (as is already the case on High DPI devices).
Thank you for your response and help. We will wait for M56 and see if scrolling performance will increased. Just one little question: can you provide a link for M56 feature which could help us with this issue?

Many thanks.
There's no link per-se because this is intended to be a pure performance improvement with no compatibility risk or visual behavior change. The relevant bug is https://bugs.chromium.org/p/chromium/issues/detail?id=381840

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