#!/usr/bin/perl

use X11::Protocol;
use IO::Select;

my $x = X11::Protocol->new();

sub res { $x->new_rsrc() };

my $eventmask = $x->pack_event_mask(qw(
	KeyPress Exposure ButtonPress ButtonRelease PointerMotion
));

$x->CreateWindow(
	my $win = res(), $x->root, 'InputOutput', $x->root_depth,
	'CopyFromParent', (0, 0, 600, 400), 1,
	'background_pixel' => $x->white_pixel,
	'event_mask' => $eventmask,
);

$x->ChangeProperty(
	$win, $x->atom("WM_NAME"), $x->atom("STRING"), 8,
	'Replace', 'Perl Paint'
);

$x->MapWindow($win);

$x->event_handler(do {

	my @lastxy;
	my $buttonpressed = 0;

	$x->CreateGC(
		my $black = res(), $win, 'foreground' => $x->black_pixel,
		'graphics_exposures' => 0
	);
	$x->CreateGC(
		my $white = res(), $win, 'foreground' => $x->white_pixel,
		'graphics_exposures' => 0
	);

	sub {
		my %e = @_;

		if ($e{name} eq 'MotionNotify') {
			$x->PolyLine($win, $black, 'Origin', @lastxy, $e{event_x}, $e{event_y})
				if $lastxy[0] and $lastxy[1] and $buttonpressed;

			@lastxy = ($e{event_x}, $e{event_y});
		} elsif ($e{name} eq 'ButtonPress') {
			@lastxy = ($e{event_x}, $e{event_y});
			$buttonpressed = 1;
		} elsif ($e{name} eq 'ButtonRelease') {
			$buttonpressed = 0;
		} elsif ($e{name} eq 'Expose') {
			$x->PolyRectangle(
				$win, $white,
				[($e{'x'}, $e{'y'}), $e{width}, $e{height}]
			);
		}
	};
});

my $sel = IO::Select->new($x->connection->fh);

while (1) {
	for my $fh ($sel->can_read) {
		$x->handle_input if $fh == $x->connection->fh;
	}
}