[Webkit-unassigned] [Bug 202696] WKWebView occasionally fails to render content when scrolling

Wed Feb 19 09:11:51 PST 2020

https://bugs.webkit.org/show_bug.cgi?id=202696

--- Comment #15 from teodor.atroshenko at gmail.com ---
(In reply to lacey from comment #13)
> Is the grey colour the same as the background colour for the body of the
> page?

<body>'s background color is white, but there are other DOM elements, opaque background of WKWebView itself and status bar colors that match exactly the color of the "blank" area that is rendered on the page. I do not have a screen capture recording of this, but the behavior is very similar to your GIF with a couple of differences:

1. When the rendering fails "above" the current content, the toolbar ("position: fixed; top: 0") remains displayed. So the "broken" area of the page does not cover it. However, in the GIF it seems like the content at the top of the page that gets covered is not part of WKWebView, so this point may not be relevant to the issue.

2. We are able to scroll the page (<body>) and in the GIF it seems like undesired scrolling is happening - there is no content overflowing the screen. However, in our case there is always content overflowing, so there is always content "below" to see, so you can always scroll the page in our case.

3. The "broken" area is not affecting the actual content of the page in your GIF. In our case, all content of <body> below or above certain scroll position would fail to render. In your case the content is still being drawn and there is something else covering it.

This may be due to some native scrolling happening somewhere. You can try running Safari Preview on Mac, connecting the iPhone (with Web Inspector enabled in Settings app for Safari), and then mousing-over the WKWebView entry on Mac's Safari in Develop -> "Your iPhone's name" -> WKWebView page URL. When you mouse over, it should highlight the WKWebView on your iPhone and you'll be able to see its bounds. Then try scrolling and see if the bounds remain the same or if they begin to change.

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