Custom Widgets
By deriving directly from Gtk::Widget you can do all the drawing for your widget directly, instead of just arranging child widgets. For instance, a Gtk::Label draws the text of the label, but does not do this by using other widgets.
When deriving from Gtk::Widget, you should override the following virtual methods. The methods marked (optional) need not be overridden in all custom widgets. The base class's methods may be appropriate.
- get_request_mode_vfunc(): (optional) Return what Gtk::SizeRequestMode is preferred by the widget.
- get_preferred_width_vfunc(): Calculate the minimum and natural width of the widget.
- get_preferred_height_vfunc(): Calculate the minimum and natural height of the widget.
- get_preferred_width_for_height_vfunc(): Calculate the minimum and natural width of the widget, if it would be given the specified height.
- get_preferred_height_for_width_vfunc(): Calculate the minimum and natural height of the widget, if it would be given the specified width.
- on_size_allocate(): Position the widget, given the height and width that it has actually been given.
- on_realize(): Associate a Gdk::Window with the widget.
- on_unrealize(): (optional) Break the association with the Gdk::Window.
- on_map(): (optional)
- on_unmap(): (optional)
- on_draw(): Draw on the supplied Cairo::Context.
The first 6 methods in the previous table are also overridden in custom containers. They are briefly described in the Custom Containers section.
Most custom widgets need their own Gdk::Window to draw on. Then you can call Gtk::Widget::set_has_window(true) in your constructor. (This is the default value.) If you do not call set_has_window(false), you must override on_realize() and call Gtk::Widget::set_realized() and Gtk::Widget::set_window() from there.
- 28.2.1. Example
28.2.1. Example
This example implements a widget which draws a Penrose triangle.
File: mywidget.h (For use with gtkmm 3, not gtkmm 2)
#ifndef GTKMM_CUSTOM_WIDGET_MYWIDGET_H
#define GTKMM_CUSTOM_WIDGET_MYWIDGET_H
#include <gtkmm/widget.h>
#include <gtkmm/cssprovider.h>
class MyWidget : public Gtk::Widget
{
public:
MyWidget();
virtual ~MyWidget();
protected:
//Overrides:
virtual Gtk::SizeRequestMode get_request_mode_vfunc() const;
virtual void get_preferred_width_vfunc(int& minimum_width, int& natural_width) const;
virtual void get_preferred_height_for_width_vfunc(int width, int& minimum_height, int& natural_height) const;
virtual void get_preferred_height_vfunc(int& minimum_height, int& natural_height) const;
virtual void get_preferred_width_for_height_vfunc(int height, int& minimum_width, int& natural_width) const;
virtual void on_size_allocate(Gtk::Allocation& allocation);
virtual void on_map();
virtual void on_unmap();
virtual void on_realize();
virtual void on_unrealize();
virtual bool on_draw(const Cairo::RefPtr<Cairo::Context>& cr);
Glib::RefPtr<Gdk::Window> m_refGdkWindow;
Glib::RefPtr<Gtk::CssProvider> m_refStyleProvider;
int m_scale;
};
#endif //GTKMM_CUSTOM_WIDGET_MYWIDGET_H
File: examplewindow.h (For use with gtkmm 3, not gtkmm 2)
#ifndef GTKMM_EXAMPLEWINDOW_H
#define GTKMM_EXAMPLEWINDOW_H
#include <gtkmm.h>
#include "mywidget.h"
class ExampleWindow : public Gtk::Window
{
public:
ExampleWindow();
virtual ~ExampleWindow();
protected:
//Signal handlers:
void on_button_quit();
//Child widgets:
Gtk::Box m_VBox;
MyWidget m_MyWidget;
Gtk::ButtonBox m_ButtonBox;
Gtk::Button m_Button_Quit;
};
#endif //GTKMM_EXAMPLEWINDOW_H
File: examplewindow.cc (For use with gtkmm 3, not gtkmm 2)
#include "examplewindow.h"
ExampleWindow::ExampleWindow()
: m_VBox(Gtk::ORIENTATION_VERTICAL),
m_Button_Quit("Quit")
{
set_title("Custom Widget example");
set_border_width(6);
set_default_size(400, 200);
add(m_VBox);
m_VBox.pack_start(m_MyWidget, Gtk::PACK_EXPAND_WIDGET);
m_MyWidget.show();
m_VBox.pack_start(m_ButtonBox, Gtk::PACK_SHRINK);
m_ButtonBox.pack_start(m_Button_Quit, Gtk::PACK_SHRINK);
m_ButtonBox.set_border_width(6);
m_ButtonBox.set_layout(Gtk::BUTTONBOX_END);
m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this, &ExampleWindow::on_button_quit) );
show_all_children();
}
ExampleWindow::~ExampleWindow()
{
}
void ExampleWindow::on_button_quit()
{
hide();
}
File: main.cc (For use with gtkmm 3, not gtkmm 2)
#include "examplewindow.h"
#include <gtkmm/application.h>
int main(int argc, char *argv[])
{
Glib::RefPtr<Gtk::Application> app = Gtk::Application::create(argc, argv, "org.gtkmm.example");
ExampleWindow window;
//Shows the window and returns when it is closed.
return app->run(window);
}
File: mywidget.cc (For use with gtkmm 3, not gtkmm 2)
#include "mywidget.h"
#include <gdkmm/general.h> // for cairo helper functions
#include <iostream>
//#include <gtk/gtkwidget.h> //For GTK_IS_WIDGET()
#include <cstring>
MyWidget::MyWidget() :
//The GType name will actually be gtkmm__CustomObject_mywidget
Glib::ObjectBase("mywidget"),
Gtk::Widget(),
m_scale(1000)
{
set_has_window(true);
//This shows the GType name, which must be used in the CSS file.
std::cout << "GType name: " << G_OBJECT_TYPE_NAME(gobj()) << std::endl;
//This shows that the GType still derives from GtkWidget:
//std::cout << "Gtype is a GtkWidget?:" << GTK_IS_WIDGET(gobj()) << std::endl;
//Install a style so that an aspect of this widget may be themed via a CSS
//style sheet file:
gtk_widget_class_install_style_property(GTK_WIDGET_CLASS(
G_OBJECT_GET_CLASS(gobj())),
g_param_spec_int("example_scale",
"Scale of Example Drawing",
"The scale to use when drawing. This is just a silly example.",
G_MININT,
G_MAXINT,
500,
G_PARAM_READABLE) );
m_refStyleProvider = Gtk::CssProvider::create();
Glib::RefPtr<Gtk::StyleContext> refStyleContext = get_style_context();
refStyleContext->add_provider(m_refStyleProvider,
GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
try
{
m_refStyleProvider->load_from_path("custom_gtk.css");
}
catch(const Glib::Error& ex)
{
std::cerr << "Gtk::CssProvider::load_from_path() failed: " << ex.what() << std::endl;
}
}
MyWidget::~MyWidget()
{
}
Gtk::SizeRequestMode MyWidget::get_request_mode_vfunc() const
{
//Accept the default value supplied by the base class.
return Gtk::Widget::get_request_mode_vfunc();
}
//Discover the total amount of minimum space and natural space needed by
//this widget.
//Let's make this simple example widget always need minimum 60 by 50 and
//natural 100 by 70.
void MyWidget::get_preferred_width_vfunc(int& minimum_width, int& natural_width) const
{
minimum_width = 60;
natural_width = 100;
}
void MyWidget::get_preferred_height_for_width_vfunc(int /* width */,
int& minimum_height, int& natural_height) const
{
minimum_height = 50;
natural_height = 70;
}
void MyWidget::get_preferred_height_vfunc(int& minimum_height, int& natural_height) const
{
minimum_height = 50;
natural_height = 70;
}
void MyWidget::get_preferred_width_for_height_vfunc(int /* height */,
int& minimum_width, int& natural_width) const
{
minimum_width = 60;
natural_width = 100;
}
void MyWidget::on_size_allocate(Gtk::Allocation& allocation)
{
//Do something with the space that we have actually been given:
//(We will not be given heights or widths less than we have requested, though
//we might get more)
//Use the offered allocation for this container:
set_allocation(allocation);
if(m_refGdkWindow)
{
m_refGdkWindow->move_resize( allocation.get_x(), allocation.get_y(),
allocation.get_width(), allocation.get_height() );
}
}
void MyWidget::on_map()
{
//Call base class:
Gtk::Widget::on_map();
}
void MyWidget::on_unmap()
{
//Call base class:
Gtk::Widget::on_unmap();
}
void MyWidget::on_realize()
{
//Do not call base class Gtk::Widget::on_realize().
//It's intended only for widgets that set_has_window(false).
set_realized();
//Get the themed style from the CSS file:
get_style_property("example_scale", m_scale);
std::cout << "m_scale (example_scale from the theme/css-file) is: "
<< m_scale << std::endl;
if(!m_refGdkWindow)
{
//Create the GdkWindow:
GdkWindowAttr attributes;
memset(&attributes, 0, sizeof(attributes));
Gtk::Allocation allocation = get_allocation();
//Set initial position and size of the Gdk::Window:
attributes.x = allocation.get_x();
attributes.y = allocation.get_y();
attributes.width = allocation.get_width();
attributes.height = allocation.get_height();
attributes.event_mask = get_events () | Gdk::EXPOSURE_MASK;
attributes.window_type = GDK_WINDOW_CHILD;
attributes.wclass = GDK_INPUT_OUTPUT;
m_refGdkWindow = Gdk::Window::create(get_parent_window(), &attributes,
GDK_WA_X | GDK_WA_Y);
set_window(m_refGdkWindow);
//set colors
override_background_color(Gdk::RGBA("red"));
override_color(Gdk::RGBA("blue"));
//make the widget receive expose events
m_refGdkWindow->set_user_data(gobj());
}
}
void MyWidget::on_unrealize()
{
m_refGdkWindow.reset();
//Call base class:
Gtk::Widget::on_unrealize();
}
bool MyWidget::on_draw(const Cairo::RefPtr<Cairo::Context>& cr)
{
const double scale_x = (double)get_allocation().get_width() / m_scale;
const double scale_y = (double)get_allocation().get_height() / m_scale;
// paint the background
Gdk::Cairo::set_source_rgba(cr, get_style_context()->get_background_color());
cr->paint();
// draw the foreground
Gdk::Cairo::set_source_rgba(cr, get_style_context()->get_color());
cr->move_to(155.*scale_x, 165.*scale_y);
cr->line_to(155.*scale_x, 838.*scale_y);
cr->line_to(265.*scale_x, 900.*scale_y);
cr->line_to(849.*scale_x, 564.*scale_y);
cr->line_to(849.*scale_x, 438.*scale_y);
cr->line_to(265.*scale_x, 100.*scale_y);
cr->line_to(155.*scale_x, 165.*scale_y);
cr->move_to(265.*scale_x, 100.*scale_y);
cr->line_to(265.*scale_x, 652.*scale_y);
cr->line_to(526.*scale_x, 502.*scale_y);
cr->move_to(369.*scale_x, 411.*scale_y);
cr->line_to(633.*scale_x, 564.*scale_y);
cr->move_to(369.*scale_x, 286.*scale_y);
cr->line_to(369.*scale_x, 592.*scale_y);
cr->move_to(369.*scale_x, 286.*scale_y);
cr->line_to(849.*scale_x, 564.*scale_y);
cr->move_to(633.*scale_x, 564.*scale_y);
cr->line_to(155.*scale_x, 838.*scale_y);
cr->stroke();
return true;
}