surface: add timer-based scrolling during selection

[moni-dz]

Adds a timer to continuously scroll during selection when outside the viewport, 15ms per line.

Currently the scrolling behavior requires you to jiggle the mouse to continuously scroll upwards/downwards when selecting text.

Before

before.mp4

After

after.mp4

[mitchellh]

Thanks for taking this on.

I do not like the idea that the renderer thread is controlling the viewport in this way or modifying the terminal at all. The renderer thread should, philosophically, be a read-only consumer of the terminal.

I like that by putting it in a thread with libxev you've made this cross-platform and just work, though.

I wonder if this should perhaps go into the IO thread instead, which spiritually owns the terminal anyways.

[moni-dz]

I do not like the idea that the renderer thread is controlling the viewport in this way or modifying the terminal at all. The renderer thread should, philosophically, be a read-only consumer of the terminal.

I wonder if this should perhaps go into the IO thread instead, which spiritually owns the terminal anyways.

I have moved the logic to the Termio thread, that seems to be the right call as sending mailbox messages became cleaner.

[moni-dz]

Now the selection region keeps up with the scrolling.