Clear scrollback buffer when clearing screen on Windows

[makew0rld]

Downstream issue: makew0rld/amfora#183

From some quick browsing of the tcell repo, it appears like clearing the screen on Windows is just done by writing some spaces? Unfortunately this is causing issues as the link describes, where a user can just scroll up and see the old screen.

The user suggests using an ANSI code, I'm not sure how portable that is on Windows. But it would seemingly solve this issue.

It's possible this is actually an issue with cview and not tcell. If you have any insight that would be appreciated.

[gdamore]

I think this is now fixed ... I'd appreciate it if you're able to retest with a recent (e.g. 2.5.1) version of tcell.

[JoeKar]

The effect shown in the video in the linked issue (makew0rld/amfora#183) looks quite similar as the effect complained with zyedidia/micro#3073. Maybe a port of the PR (zyedidia#26) for the tcell fork could help here too.

[gdamore]

I'm confused by the request here.

Do you not want to allow the screen to scroll? You want to kill the scrollback buffer? Why?

The problem with issuing an escape (or using an underlying screen clear) is that it causes flashing on screen updates, which is annoying.

The complaint about mouse scrolling is a separate issue, which relates to whether we capture the scrolling for application use or leave it to the terminal application. And ultimately we are limited by what the terminal will actually honor.

The downstream amphora issue should be related to clearing the screen when the screen is resized (which ideally should also be emitted if changing the font changes the amount of characters visible in the screen.)

We should use a hard clear on such situations. This can be effected by the application using screen.Sync() (which is used to repair e.g.screen damage if a background application scribbles to the screen -- traditionally UNIX applications use Ctrl-L to clear and redraw the screen to recover from "screen damage".) But this should happen automatically if the Terminal informs us that the screen size changed. (On UNIX we rely on a signal -- SIGWINCH -- to detect this. In Windows I believe we look for this as an "event" in the same way we receive mouse events, etc.)

[gdamore]

I believe there is nothing more actionable for me to do. We are now using VT mode by default. This should achieve what is needed.