Bug 211870 – A portion of the WebGL canvas is not updated at all, after rotating the phone from the portrait mode to the landscape mode and then to the portrait mode again

• Component: WebGL
• Status: NEW

[Kei Kim]

Created attachment 399315 [details]
The screen recording of the bug

Example URL:
https://newvr.s3.ap-northeast-2.amazonaws.com/vrshowroom/csa/csa0/lhdfull/index.html#sp2iexterior

Steps to reproduce the problem:
1. Open the url and wait to load the scene. Click the round button to open the webgl view.
2. Rotate the phone to the landscape mode so that the screen can rotate accordingly
3. Rotate the phone back to the portrait mode and see if the bottom part of the canvas is not updating. Repeat from #2, if this didn’t happen.
4. Now press the tab button of Chrome. Select the tab and see that the entire canvas is updating correctly.

What is the expected behavior?
The entire WebGL canvas should be updated no matter if a user has rotated the screen multiple times

What went wrong?
After quickly rotating a couple of times, some portion of the WebGL canvas is not updating at all. When I checked the canvas size, it occupies the entire screen. Also, as soon as I clicked the tab button to minimize the window for a while and came back to the same tab, the screen was updating normally.

Does it occur on multiple sites: Yes

Does this work in other browsers? Yes

Which browsers are affected? Safari 13 (iOS), Chrome 81.0.4044.124 (iOS)

OS Version: iOS 13.4.1

Another website with the same problem:
http://kiavr2017.s3-website.ap-northeast-2.amazonaws.com/handson/cn/cn1/#bdcexterior

[Radar WebKit Bug Importer]

<rdar://problem/63208984>

[Kei Kim]

To workaround this issue, I needed to change the canvas size a couple of time when the canvas size is changed.

For the link,
https://newvr.s3.ap-northeast-2.amazonaws.com/vrshowroom/csa/csa0/lhdfull/index.html#sp2iexterior

this patch is applied. When the canvas's size is changed, that grey undrawn area is correctly updated again.

For another link,
http://kiavr2017.s3-website.ap-northeast-2.amazonaws.com/handson/cn/cn1/#bdcexterior

the patch is not applied.
You can test with the latter link. Just rotate the screen a couple of time from the portrait mode to the landscape mode and vice versa.

Thanks.