UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36

Steps to reproduce the problem:
1. Load test case (attached, but also available at http://bl.ocks.org/lbud/raw/42e74264e3ef6c92cd677ea565445050/ )
2. Toggle both buttons on to set canvas border-radius > 0px & overflow = hidden

What is the expected behavior?
Smooth animation

What went wrong?
The animation stutters, as if occasionally swapping frames with previous frames (creating the appearance in this case of the rotation occasionally stuttering backward).

Setting the WebGL canvas's border-radius to > 0px and/or setting overflow to hidden greatly exacerbate the effect (presumably due to compositing?), but the stutter can also be reproduced without either property.

I'm attaching a screen capture of what I see — if I do some unburdening of my CPU the effect is lessened but still easily reproduced.

I'm on a 2016 13" MacBook Pro with Intel Iris Graphics 550 1536 MB.
My colleagues with 15" Macbook Pros with AMD Radeon Pro 450 chips are able to just barely reproduce this, much more subtly. 

This was originally reported in the Mapbox GL project — https://github.com/mapbox/mapbox-gl-js/issues/5333 provides some context behind the investigation of properties that exacerbate this. Here's a reduced map test case that demonstrates the fact, as mentioned in that ticket, that the stutter is severely exacerbated when the canvas is unfocused: https://bl.ocks.org/lbud/raw/632c6afc8f51c5907f3857893bf3062b/ . Note that I believe there's a second (maybe related? — will file separately) bug wherein Chrome isn't correctly detecting the end of the frame — once the map has loaded, click on the map to finish the first load, then zoom in and out quickly with the map focused and it should look mostly fine. Then click outside of the map to unfocus but zoom in and out with the trackpad to see severe flickering. I'm attaching a second video demonstrating this in a map (initially with the map focused, then unfocused).

Did this work before? Yes Chrome 60

Does this work in other browsers? Yes

Chrome version: 61.0.3163.100  Channel: stable
OS Version: OS X 10.12.6
Flash Version:
 

Deleted: stutter.html 5.6 KB

stutter.html 5.6 KB View Download

Deleted: 20171010_webgl_stutter.mov 855 KB

20171010_webgl_stutter.mov 855 KB Download

Deleted: 20171010_webgl_stutter_map.mov 26.5 MB

20171010_webgl_stutter_map.mov 26.5 MB Download