Support for getting terminal width & height

[richard-uk1]

Getting the terminal width and height is something you cannot do presently with the Terminal trait. It prevents implementation of something like termbox on top of Terminal trait.

The linux implementation looks something like (from termbox)

    struct winsize sz;
    memset(&sz, 0, sizeof(sz));

    ioctl(inout, TIOCGWINSZ, &sz);

    termw = sz.ws_col;
    termh = sz.ws_row;

whilst in windows the relevant function is kernel32::GetConsoleScreenBufferInfo

[richard-uk1]

I've had a look at implementing this - the main problem as I see it is that currently the unix implementation does everything with terminfo, therefore not needing to make any system calls directly. The best way to get the console dimensions is to issue an ioctl to populate the winsize struct, but that may not be possible with serial consoles for example.

According to https://unix.stackexchange.com/questions/93173/how-does-less-know-the-terminal-resolution the program less takes the approach of using ioctl if available, and then using some tricks to try and figure out the width/height (e.g. environment variables).

So questions:

1. Do you want/mind linking to libc on linux?
2. Do you therefore think that the size function should return an Option, with none if it wasn't possible to calculate the size?

[richard-uk1]

You can see my messings about at https://github.com/derekdreery/term :master

[Stebalien]

1. I'm fine with that.
2. When Error handling overhaul #49 gets merged, we can use a NotSupported error variant.

As for getting this working on unix, given that #49 will be a breaking change anyways I plan on reworking the internals quite a bit (after it lands) so this will probably get much easier.

[richard-uk1]

http://docs.freebsd.org/44doc/usd/13.viref/paper.html#section5f seems like a good strategy?

[Stebalien]

@derekdreery Yes, that looks good. However, I'm probably going to reorder those a bit (use ioctl first, then the environment, then the terminfo database.

[xSke]

Would this be possible in Windows too?

[Stebalien]

Yes but I won't be able to do that myself (I don't use windows).

[richard-uk1]

I put the windows function on the top of this thread - I can implement it - waiting on some constants in libc at the moment

[richard-uk1]

... a long time later

I've submitted PR #77 to implement this.