Line display issues

[LiHRaM]

Summary

xi-win sometimes seems to have trouble displaying more than 12 contiguous lines

1. File save/open
2. Using the mouse to move the cursor
3. Selections

Steps to reproduce

1. Open file with more than 12 lines
2. Hold shift + down arrow keys and watch the fireworks

There seem to be a lot of ways you can make lines disappear. I've noticed that sometimes when I click on a line with the mouse, an arbitrary line elsewhere in the file will go blank.

[raphlinus]

Yes, definitely a problem. After playing with it a bit, I think this is because update_viewport is often not being called when it should, so core has an inaccurate model of the viewport and thus fails to keep visible lines up to date. At the least, a call to EditView::size should update the viewport.

As partial explanation, this probably got broken when the EditView was reimplemented as a widget for xi-win-ui, rather than directly on top of the shell. But I haven't checked the code history; it's possible it never worked correctly, though I do see efforts to update the viewport on, for example, scrolling through mousewheel and ctrl-up/down.

Thanks for looking into it!