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Gnome2::Canvas(3pm)   User Contributed Perl Documentation  Gnome2::Canvas(3pm)

NAME
       Gnome2::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 ALSO
       Gnome2::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)
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