Gnome2::Canvas(3pm) User Contributed Perl Documentation Gnome2::Canvas(3pm)NAMEGnome2::Canvas - A structured graphics canvas
SYNOPSIS
use strict;
use Gtk2 -init;
use Gnome2::Canvas;
my $window = Gtk2::Window->new;
my $scroller = Gtk2::ScrolledWindow->new;
my $canvas = Gnome2::Canvas->new;
$scroller->add ($canvas);
$window->add ($scroller);
$window->set_default_size (150, 150);
$canvas->set_scroll_region (0, 0, 200, 200);
$window->show_all;
my $root = $canvas->root;
Gnome2::Canvas::Item->new ($root, 'Gnome2::Canvas::Text',
x => 20,
y => 15,
fill_color => 'black',
font => 'Sans 14',
anchor => 'GTK_ANCHOR_NW',
text => 'Hello, World!');
my $box = Gnome2::Canvas::Item->new ($root, 'Gnome2::Canvas::Rect',
x1 => 10, y1 => 5,
x2 => 150, y2 => 135,
fill_color => 'red',
outline_color => 'black');
$box->lower_to_bottom;
$box->signal_connect (event => sub {
my ($item, $event) = @_;
warn "event ".$event->type."\n";
});
Gtk2->main;
DESCRIPTION
The Gnome Canvas is an engine for structured graphics that offers a
rich imaging model, high-performance rendering, and a powerful, high
level API. It offers a choice of two rendering back-ends, one based on
GDK for extremely fast display, and another based on Libart, a
sophisticated, antialiased, alpha-compositing engine. This widget can
be used for flexible display of graphics and for creating interactive
user interface elements.
To create a new Gnome2::Canvas widget call "Gnome2::Canvas->new" or
"Gnome2::Canvas->new_aa" for an anti-aliased mode canvas.
A Gnome2::Canvas contains one or more Gnome2::CanvasItem objects. Items
consist of graphing elements like lines, ellipses, polygons, images,
text, and curves. These items are organized using Gnome2::CanvasGroup
objects, which are themselves derived from Gnome2::CanvasItem. Since a
group is an item it can be contained within other groups, forming a
tree of canvas items. Certain operations, like translating and
scaling, can be performed on all items in a group.
There is a special root group created by a Gnome2::Canvas. This is the
top level group under which all items in a canvas are contained. The
root group is available as "$canvas->root".
There are several different coordinate systems used by Gnome2::Canvas
widgets. The primary system is a logical, abstract coordinate space
called world coordinates. World coordinates are expressed as unbounded
double floating point numbers. When it comes to rendering to a screen
the canvas pixel coordinate system (also referred to as just canvas
coordinates) is used. This system uses integers to specify screen
pixel positions. A user defined scaling factor and offset are used to
convert between world coordinates and canvas coordinates. Each item in
a canvas has its own coordinate system called item coordinates. This
system is specified in world coordinates but they are relative to an
item (0.0, 0.0 would be the top left corner of the item). The final
coordinate system of interest is window coordinates. These are like
canvas coordinates but are offsets from within a window a canvas is
displayed in. This last system is rarely used, but is useful when
manually handling GDK events (such as drag and drop) which are
specified in window coordinates (the events processed by the canvas are
already converted for you).
Along with different coordinate systems come methods to convert between
them. "$canvas->w2c" converts world to canvas pixel coordinates and
"canvas->c2w" converts from canvas to world. To get the affine
transform matrix for converting from world coordinates to canvas
coordinates call "$canvas->w2c_affine". "$canvas->window_to_world"
converts from window to world coordinates and
"$canvas->world_to_window" converts in the other direction. There are
no methods for converting between canvas and window coordinates, since
this is just a matter of subtracting the canvas scrolling offset. To
convert to/from item coordinates use the methods defined for
Gnome2::CanvasItem objects.
To set the canvas zoom factor (canvas pixels per world unit, the
scaling factor) call "$canvas->set_pixels_per_unit"; setting this to
1.0 will cause the two coordinate systems to correspond (e.g., [5, 6]
in pixel units would be [5.0, 6.0] in world units).
Defining the scrollable area of a canvas widget is done by calling
"$canvas->set_scroll_region" and to get the current region
"$canvas->get_scroll_region" can be used. If the window is larger than
the canvas scrolling region it can optionally be centered in the
window. Use "$canvas->set_center_scroll_region" to enable or disable
this behavior. To scroll to a particular canvas pixel coordinate use
"$canvas->scroll_to" (typically not used since scrollbars are usually
set up to handle the scrolling), and to get the current canvas pixel
scroll offset call "$canvas->get_scroll_offsets".
HIERARCHY
Glib::Object
+----Glib::InitiallyUnowned
+----Gtk2::Object
+----Gtk2::Widget
+----Gtk2::Container
+----Gtk2::Layout
+----Gnome2::Canvas
INTERFACES
Glib::Object::_Unregistered::AtkImplementorIface
Gtk2::Buildable
METHODS
widget = Gnome2::Canvas->new
Create a new empty canvas in non-antialiased mode.
widget = Gnome2::Canvas->new_aa
Create a new empty canvas in antialiased mode.
boolean = $canvas->aa
Returns true if $canvas was created in anti-aliased mode.
($bx1, $by1, $bx2, $by2) = Gnome2::Canvas->get_butt_points ($x1, $y1, $x2,
$y2, $width, $project)
· $x1 (double)
· $y1 (double)
· $x2 (double)
· $y2 (double)
· $width (double)
· $project (integer)
(wx, wy) = $canvas->c2w ($cx, $cy)
· $cx (integer)
· $cy (integer)
boolean = $canvas->get_center_scroll_region
$canvas->set_center_scroll_region ($center_scroll_region)
· $center_scroll_region (boolean)
list = $canvas->get_color ($spec)
· $spec (string)
Returns an integer indicating the success of the color allocation
and a GdkColor.
unsigned = $canvas->get_color_pixel ($rgba)
· $rgba (integer)
rgbdither = $canvas->get_dither
$canvas->set_dither ($dither)
· $dither (Gtk2::Gdk::RgbDither)
item = $canvas->get_item_at ($x, $y)
· $x (double)
· $y (double)
($mx1, $my1, $mx2, $my2) = Gnome2::Canvas->get_miter_points ($x1, $y1, $x2,
$y2, $x3, $y3, $width)
· $x1 (double)
· $y1 (double)
· $x2 (double)
· $y2 (double)
· $x3 (double)
· $y3 (double)
· $width (double)
double = $canvas->get_pixels_per_unit
Fetch $canvas' scale factor.
$canvas->set_pixels_per_unit ($n)
· $n (double)
Set the zooming factor of $canvas by specifying the number of
screen pixels that correspond to one canvas unit.
double = Gnome2::Canvas->polygon_to_point ($poly_ref, $x, $y)
· $poly_ref (arrayref) coordinate pairs that make up the polygon
· $x (double)
· $y (double)
Return the distance from the point $x,$y to the polygon described
by the vertices in $poly_ref, or zero if the point is inside the
polygon.
$canvas->request_redraw ($x1, $y1, $x2, $y2)
· $x1 (integer)
· $y1 (integer)
· $x2 (integer)
· $y2 (integer)
group = $canvas->root
(cx, cy) = $canvas->get_scroll_offsets
(x1, y1, x2, y2) = $canvas->get_scroll_region
$canvas->set_scroll_region ($x1, $y1, $x2, $y2)
· $x1 (double)
· $y1 (double)
· $x2 (double)
· $y2 (double)
$canvas->scroll_to ($cx, $cy)
· $cx (integer)
· $cy (integer)
$canvas->set_stipple_origin ($gc)
· $gc (Gtk2::Gdk::GC)
$canvas->update_now
(cx, cy) = $canvas->w2c ($wx, $wy)
· $wx (double)
· $wy (double)
$affine = $canvas->w2c_affine
Fetch the affine transform that converts from world coordinates to
canvas pixel coordinates.
Note: This method was completely broken for all
$Gnome2::Canvas::VERSION < 1.002.
(cx, cy) = $canvas->w2c_d ($wx, $wy)
· $wx (double)
· $wy (double)
(worldx, worldy) = $canvas->window_to_world ($winx, $winy)
· $winx (double)
· $winy (double)
(winx, winy) = $canvas->world_to_window ($worldx, $worldy)
· $worldx (double)
· $worldy (double)
PROPERTIES
'aa' (boolean : readable / writable / construct-only)
The antialiasing mode of the canvas.
'focused-item' (Gnome2::Canvas::Item : readable / writable)
SIGNALS
draw-background (Gnome2::Canvas, Gtk2::Gdk::Drawable, integer, integer,
integer, integer)
render-background (Gnome2::Canvas, gpointer)
ENUMS AND FLAGS
enum Gtk2::Gdk::RgbDither
· 'none' / 'GDK_RGB_DITHER_NONE'
· 'normal' / 'GDK_RGB_DITHER_NORMAL'
· 'max' / 'GDK_RGB_DITHER_MAX'
SEE ALSOGnome2::Canvas::index(3pm) lists the generated Perl API reference PODs.
Frederico Mena Quintero's whitepaper on the GNOME Canvas:
http://developer.gnome.org/doc/whitepapers/canvas/canvas.html
The real GnomeCanvas is implemented in a C library; the Gnome2::Canvas
module allows a Perl developer to use the canvas like a normal
gtk2-perl object. Like the Gtk2 module on which it depends,
Gnome2::Canvas follows the C API of libgnomecanvas-2.0 as closely as
possible while still being perlish. Thus, the C API reference remains
the canonical documentation; the Perl reference documentation lists
call signatures and argument types, and is meant to be used in
conjunction with the C API reference.
GNOME Canvas Library Reference Manual
http://developer.gnome.org/doc/API/2.0/libgnomecanvas/index.html
perl(1), Glib(3pm), Gtk2(3pm).
To discuss gtk2-perl, ask questions and flame/praise the authors, join
gtk-perl-list@gnome.org at lists.gnome.org.
AUTHOR
muppet <scott at asofyet dot org>, with patches from Torsten Schoenfeld
<kaffetisch at web dot de>.
The DESCRIPTION section of this page is adapted from the documentation
of libgnomecanvas.
COPYRIGHT AND LICENSE
Copyright 2003-2004 by the gtk2-perl team.
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Library General Public License as published
by the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307
USA.
perl v5.10.0 2009-02-02 Gnome2::Canvas(3pm)