libvterm/pangoterm and Tickit

Lately I've written a bit about my terminal emulator library, libvterm, and briefly mentioned Tickit, my terminal UI module for Perl. I'll write about each in more detail soon, but I thought since I hit an important milestone recently, I'd write a little something more about libvterm and pangoterm.

libvterm is a purely abstract C99 library that implements the bulk of the logic of being a terminal emulator. Bytes from the PTY master are fed into it by the containing program, and it maintains the abstract state of the terminal; the position of the cursor, the state of the pen, what charcters are where with what attributes, and so on. It calls callback functions registered by the containing program, to inform it of damaged screen regions that need repainting. Two of the main selling points of the library are

• It is purely abstract C99, doesn't rely on POSIX or any particular rendering/UI system


• During normal operation of just feeding it bytes and processing events, it does not use the malloc system.

These properties make it ideal for a number of situations, ranging from desktop applications, to small embedded systems or operating system kernels.

pangoterm is a GTK/Pango-driven embedding of this libary, in a simple single-.c-file application, mostly for me to develop and test it. It is currently maintained in the libvterm source tree.

For a while now this combination has been complete enough to drive vim sufficient to edit its own source code - pangoterm and libvterm are now self-hosting. A couple of weeks ago I finally managed to fix the last of a number of small issues making it not quite perfect. Last week I also managed to get pangoterm to completely correctly render a Tickit-based program; the final missing piece being some of the mouse tracking modes.

I now have a bit of extra configuration in my .vimrc to take advantage of a few of pangoterm's abilities, such as support for italics.


As well as italics, it also supports strikethrough and alternative fonts, although so far I've only managed to find one alternative font that actually looks at all decent alongside DejaVu Sans Mono. These are all shown off quite well by Tickit's demo-pen.pl example script here.


And finally here, a demo of the xterm-like 256 colour handling.


These screenshots briefly show Tickit working nicely with pangoterm. Sometime soon I shall get around to writing about Tickit in more detail, and also explaining some of my further plans for the whole Tickit+libtermkey vs libvterm combination.

Perl - Sentinel - version 0.02

I have just uploaded the first (non-development) release of Sentinel; version 0.02.

It provides a little helper function that creates lvalues, suitable for lvalue typed accessors that want to run real code on assignment (such as for type checking or coercion, or update triggers), rather than just update a scalar.

use Sentinel;
 
sub foo :lvalue
{
   my $self = shift;
   sentinel get => sub { return $self->get_foo },
            set => sub { $self->set_foo( $_[0] ) };
}

It makes the following two lines equivalent

my $obj = Some::Object->new;

$obj->set_foo( 100 );
$obj->foo = 100;

This is rare among my modules, more or less the first thing I've written mostly as a result of ranting about it on #perl, rather than because I actually wanted it. My argument kept being that if anyone does want an lvalue accessor, it's trivially easy to write one given some function sentinel as in this example, and that actually implementing the sentinel function itself isn't hard; it's a small piece of obvious XS magic.

So here it is.

It has to cheat somewhat on versions of Perl before 5.14, because of the way lvalue context isn't properly as powerful as it now is. Long story short - there may be unit-test failures on some older versions of Perl; but I can't tell yet because the CPAN Testers web frontend is still down, so I can't see the smokers. If anyone sees any version-related failures, please do let me know.

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Edit 2011/11/29: By the power of crowdsourced smoke testing, it appears this does work stably across many Perl versions - thanks all who've informed me.