Fixes#2815
This commit changes our autoscroll strategy for cursors significantly.
Originally, we were autoscrolling whenever the cursor's marker changed
positions. This worked well, except we didn't end up autoscrolling when
the user *attempted* to move the cursor to an invalid position, such as
moving down at the end of the buffer, due to the fact that the marker
wouldn't change.
Then, we moved to always requesting an autoscroll whenever a position
change was requested via Cursor::changePosition. This missed out on
moving the cursor when inserting text, so we then also added an explicit
autoscroll call when inserting text.
This had the problem of not autoscrolling due to undo. So finally, this
solution combines explicit autoscroll in ::changePosition to capture
intent, as well as implicit autoscrolling whenever the cursor's marker
position changes due to a textual change in the buffer. This captures
undo/redo correctly.
Fixes#2810
The line corresponding to the longest screen row moves when lines are
inserted or removed above it, so we need to adjust it accordingly or we
won't always realize when a change affects the longest line.
This prevents feedback loops where we handle stale 'scroll' events
for scrolls requested in the model layer. It prevents jitter when
autoscrolling with the cursor.
I previously thought this was okay, but now I'm experiencing jitter when
scrolling with the trackpad when updates are deferred, and the frames
seem jagged. So this commit restores a synchronous approach to display
updates whenever we use animation frames.
Refs #2732
Because we're only checking the length of the input element's selection
in the React editor on textinput events and not also its content, we
were mistaking some IME compositions as accented character menu
insertions. Clearing the content of the input on 'compositionend'
prevents this issue.
