scrolling twitchy on iOS with line wrapping

[rapnuss]

Describe the issue

When you activate line wrapping and nothing else and paste a large amount of text with long lines,
you end up at the bottom of the text.
If you now scroll up it jumps up and down.

It only happens on iOS.

Browser and platform

iOS Safari with and without keyboard

Reproduction link

https://codesandbox.io/p/sandbox/tender-violet-mxz9tl

[marijnh]

I've finally dug into this. What is happening is that, though CodeMirror has its own logic to 'stabilize' the visible content when the (estimated or real) height of content above the visible text changes, Safari does a thing where, during a scroll drag, it will move the scroll position absolutely, based on the position where the drag started, rather than relatively to the current scroll position. The effect of this is that the library's scroll adjustment is immediately overwritten again by the browser, as it continues to scroll, causing the visible jumps you're seeing.

It would theoretically be possible to work around this by, instead of adjusting the scroll position, adjusting the positioning of the visible content. But that would require scary complicated changes in the way the editor's position management works, which is already gnarly as it is. So, though I agree this behavior is annoying, I'm going to say it is a browser issue that isn't disruptive enough to incur the cost of a workaround.