## Incremental computation
We would like to avoid redrawing all row(s) when an event occurs.
Currently, we redraw all row(s) except when:
* a character is inserted at the end of input (and there is no hint and no `highlight_char`),
* only the cursor is moved (input is not touched and no `highlight_char`).
Ideally, we would like to redraw only impacted row(s) / cell(s).
### Observable values
Currently, we assume that highlighting does not impact layout / rendered text size.
So only the following observables impact layout:
* prompt (interactive search, [input mode indicator](https://github.com/kkawakam/rustyline/pull/369)),
* [input mode](https://github.com/kkawakam/rustyline/pull/369),
* line(s) buffer,
* cursor position,
* hint / input validation message,
* screen size (line wrapping),
* [prompt continuation](https://github.com/kkawakam/rustyline/pull/372)s,
* row/wrap count.
Some other values may impact layout but they are/should be constant:
* tab stop,
### Line wrapping and highlighting
Currently, there is no word wrapping (only grapheme wrapping).
But we highlight the whole input at once.
So there is no issue: for example, even if a keyword is wrapped, style is preserved.
With [prompt continuation](https://github.com/kkawakam/rustyline/pull/372)s,
we (will) interleave user input with continuations.
So we need to preserve style.
TODO How prompt_toolkit handle this problem ?
Maybe using ANSI sequence directly was a bad idea. If `Highlighter` returns style ranges,
applying style on input slice is easy (and also supporting styles on Windows < 10).
### Impacts
Current granularity:
* PUSH_CHAR at end of input
* BEEP
* MOVE_CURSOR
* REFRESH whole input / rows
* CLEAR_SCREEN (+REFRESH)
Wanted additional granurality:
* PUSH_STRING at end of input
* REFRESH_DIRTY only rows / cells