Text is drawn via Pango Layouts. The easiest way to create a
Pango::Layout
is to use
Gtk::Widget::create_pango_layout()
.
Once created, the layout can be manipulated in various ways,
including changing the text, font, etc. Finally, the layout can
be rendered using the
Pango::Layout::show_in_cairo_context()
method.
Here is an example of a program that draws some text, some of it upside-down. The Printing chapter contains another example of drawing text.
File: myarea.h
(For use with gtkmm 4)
#ifndef GTKMM_EXAMPLE_MYAREA_H
#define GTKMM_EXAMPLE_MYAREA_H
#include <gtkmm/drawingarea.h>
class MyArea : public Gtk::DrawingArea
{
public:
MyArea();
virtual ~MyArea();
protected:
void on_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
private:
void draw_rectangle(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);
void draw_text(const Cairo::RefPtr<Cairo::Context>& cr, int rectangle_width, int rectangle_height);
};
#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("Drawing text example");
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"
MyArea::MyArea()
{
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)
{
const int rectangle_width = width;
const int rectangle_height = height / 2;
// Draw a black rectangle
cr->set_source_rgb(0.0, 0.0, 0.0);
draw_rectangle(cr, rectangle_width, rectangle_height);
// and some white text
cr->set_source_rgb(1.0, 1.0, 1.0);
draw_text(cr, rectangle_width, rectangle_height);
// flip the image vertically
// see http://www.cairographics.org/documentation/cairomm/reference/classCairo_1_1Matrix.html
// the -1 corresponds to the yy part (the flipping part)
// the height part is a translation (we could have just called cr->translate(0, height) instead)
// it's height and not height / 2, since we want this to be on the second part of our drawing
// (otherwise, it would draw over the previous part)
Cairo::Matrix matrix(1.0, 0.0, 0.0, -1.0, 0.0, height);
// apply the matrix
cr->transform(matrix);
// white rectangle
cr->set_source_rgb(1.0, 1.0, 1.0);
draw_rectangle(cr, rectangle_width, rectangle_height);
// black text
cr->set_source_rgb(0.0, 0.0, 0.0);
draw_text(cr, rectangle_width, rectangle_height);
}
void MyArea::draw_rectangle(const Cairo::RefPtr<Cairo::Context>& cr,
int width, int height)
{
cr->rectangle(0, 0, width, height);
cr->fill();
}
void MyArea::draw_text(const Cairo::RefPtr<Cairo::Context>& cr,
int rectangle_width, int rectangle_height)
{
// https://gnome.pages.gitlab.gnome.org/pangomm/classPango_1_1FontDescription.html
Pango::FontDescription font;
font.set_family("Monospace");
font.set_weight(Pango::Weight::BOLD);
// https://gnome.pages.gitlab.gnome.org/pangomm/classPango_1_1Layout.html
auto layout = create_pango_layout("Hi there!");
layout->set_font_description(font);
int text_width;
int text_height;
//get the text dimensions (it updates the variables -- by reference)
layout->get_pixel_size(text_width, text_height);
// Position the text in the middle
cr->move_to((rectangle_width-text_width)/2, (rectangle_height-text_height)/2);
layout->show_in_cairo_context(cr);
}