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<tr><th colspan="3" align="center">Drawing Text</th></tr>
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<th width="60%" align="center">Chapter 18. The DrawingArea Widget</th>
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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-drawing-text"></a>Drawing Text</h2></div></div></div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="drawing-text-pango"></a>Drawing Text with Pango</h3></div></div></div>
<p>
Text is drawn via Pango Layouts. The easiest way to create a
<code class="classname">Pango::Layout</code> is to use
<code class="methodname">Gtk::Widget::create_pango_layout()</code>.
Once created, the layout can be manipulated in various ways,
including changing the text, font, etc. Finally, the layout can
be rendered using the
<code class="methodname">Pango::Layout::show_in_cairo_context()</code> method.
</p>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="pango-text-example"></a>Example</h3></div></div></div>
<p>
Here is an example of a program that draws some text, some of it
upside-down. The Printing chapter contains another
<a class="link" href="sec-printing-examples.html" title="Examples">example</a> of drawing text.
</p>
<div class="figure">
<a name="figure-drawingarea-pango-text"></a><p class="title"><b>Figure 18.6. Drawing Area - Text</b></p>
<div class="figure-contents">
<div class="screenshot">
<div class="mediaobject"><img src="figures/drawingarea_pango_text.png" alt="Drawing Area - Text"></div>
</div>
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<br class="figure-break">
<p><a class="ulink" href="https://gitlab.gnome.org/GNOME/gtkmm-documentation/tree/master/examples/book/drawingarea/pango_text" target="_top">Source Code</a></p>
<p>File: <code class="filename">myarea.h</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#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
</code></pre>
<p>File: <code class="filename">main.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#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);
}
</code></pre>
<p>File: <code class="filename">myarea.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#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);
}
</code></pre>
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