There is a method for drawing from a
Gdk::Pixbuf
to a
Cairo::Context
.
A
Gdk::Pixbuf
buffer is a useful wrapper
around a collection of pixels, which can be read from files, and
manipulated in various ways.
Probably the most common way of creating
Gdk::Pixbuf
s is to use
Gdk::Pixbuf::create_from_file()
or
Gdk::Pixbuf::create_from_resource()
,
which can read an image file, such as a png file into a pixbuf
ready for rendering.
The
Gdk::Pixbuf
can be rendered by setting
it as the source pattern of the Cairo context with
Gdk::Cairo::set_source_pixbuf()
.
Then draw the image with either
Cairo::Context::paint()
(to draw the whole image), or
Cairo::Context::rectangle()
and
Cairo::Context::fill()
(to fill the
specified rectangle).
set_source_pixbuf()
is not a member of
Cairo::Context
. It takes
a
Cairo::Context
as its first parameter.
Here is a small bit of code to tie it all together: (Note that
usually you wouldn't load the image every time in the draw
signal handler! It's just shown here to keep it all together.)
void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
auto image = Gdk::Pixbuf::create_from_file("myimage.png");
// Draw the image at 110, 90, except for the outermost 10 pixels.
Gdk::Cairo::set_source_pixbuf(cr, image, 100, 80);
cr->rectangle(110, 90, image->get_width()-20, image->get_height()-20);
cr->fill();
Example
Here is an example of a simple program that draws an image.
The program loads the image from a resource file. See the Gio::Resource and glib-compile-resources
section. Use glib-compile-resources to compile
the resources into a C source file that can be compiled and
linked with the C++ code. E.g.
$ glib-compile-resources --target=resources.c --generate-source image.gresource.xml
Figure 18.7. Drawing Area - Image
File: myarea.h (For use with gtkmm 4)
#ifndef GTKMM_EXAMPLE_MYAREA_H
#define GTKMM_EXAMPLE_MYAREA_H
#include <gtkmm/drawingarea.h>
#include <gdkmm/pixbuf.h>
class MyArea : public Gtk::DrawingArea
public:
MyArea();
virtual ~MyArea();
protected:
void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
Glib::RefPtr<Gdk::Pixbuf> m_image;
#endif // GTKMM_EXAMPLE_MYAREA_H
File: main.cc (For use with gtkmm 4)
#include "myarea.h"
#include <gtkmm/application.h>
#include <gtkmm/window.h>
class ExampleWindow : public Gtk::Window
public:
ExampleWindow();
protected:
MyArea m_area;
ExampleWindow::ExampleWindow()
set_title("DrawingArea");
set_default_size(300, 200);
set_child(m_area);
int main(int argc, char** argv)
auto app = Gtk::Application::create("org.gtkmm.example");
return app->make_window_and_run<ExampleWindow>(argc, argv);
File: myarea.cc (For use with gtkmm 4)
#include "myarea.h"
#include <cairomm/context.h>
#include <giomm/resource.h>
#include <gdkmm/general.h> // set_source_pixbuf()
#include <glibmm/fileutils.h>
#include <iostream>
MyArea::MyArea()
// The fractal image has been created by the XaoS program.
// http://xaos.sourceforge.net
m_image = Gdk::Pixbuf::create_from_resource("/image/fractal_image.png");
catch(const Gio::ResourceError& ex)
std::cerr << "ResourceError: " << ex.what() << std::endl;
catch(const Gdk::PixbufError& ex)
std::cerr << "PixbufError: " << ex.what() << std::endl;
// Show at least a quarter of the image.
if (m_image)
set_content_width(m_image->get_width()/2);
set_content_height(m_image->get_height()/2);
// Set the draw function.
set_draw_func(sigc::mem_fun(*this, &MyArea::on_draw));
MyArea::~MyArea()
void MyArea::on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height)
if (!m_image)
return;
// Draw the image in the middle of the drawing area, or (if the image is
// larger than the drawing area) draw the middle part of the image.
Gdk::Cairo::set_source_pixbuf(cr, m_image,
(width - m_image->get_width())/2, (height - m_image->get_height())/2);
cr->paint();
File: image.gresource.xml (For use with gtkmm 4)
<?xml version="1.0" encoding="UTF-8"?>
<gresources>
<gresource prefix="/image">
<file>fractal_image.png</file>
</gresource>
</gresources>
