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#!/usr/bin/perl -w use strict; use Gtk2 '-init'; use Cairo; my $supports_alpha; sub expose { my($widget, $event) = @_; my($width, $height, $radius); my $cr = Gtk2::Gdk::Cairo::Context->create($widget->window()); if($supports_alpha) { $cr->set_source_rgba(1.0, 1.0, 1.0, 0.0); } else { $cr->set_source_rgb(1.0, 1.0, 1.0); } $cr->set_operator('source'); $cr->paint(); $cr->set_source_rgba(1.0, 0.2, 0.2, 0.6); ($width, $height) = $widget->get_size(); if($width < $height) { $radius = $width/2 - 0.8; } else { $radius = $height/2 - 0.8; } $cr->arc($width/2, $height/2, $radius, 0, 2.0*3.14); $cr->fill(); $cr->stroke(); } sub screen_changed { my ($widget, $old_screen) = @_; my $screen = $widget->get_screen(); my $colormap = $screen->get_rgba_colormap(); if(!$colormap){ print "Your screen doesn't support alpha channels!\n"; $colormap = $screen->get_rgb_colormap(); } else { $supports_alpha = 1; print "Your screen does support alpha channels!\n"; } $widget->set_colormap($colormap); } sub main { my $window = Gtk2::Window->new(); $window->set_title("Alpha Demo"); $window->set_app_paintable('TRUE'); $window->signal_connect('delete_event', \&quit); $window->signal_connect('expose_event', \&expose, $window); $window->signal_connect('screen_changed', \&screen_changed, $window); screen_changed($window); $window->show_all(); Gtk2->main; } sub quit { exit; } main();

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