Custom Widgets
| Chapter 26. Custom Widgets |

## 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.

### Example

This example implements a widget which draws a Penrose triangle.

Figure 26.2. Custom Widget

Source Code

File: `mywidget.h`

    #ifndef GTKMM_CUSTOM_WIDGET_MYWIDGET_H
    #define GTKMM_CUSTOM_WIDGET_MYWIDGET_H

    #include <gtkmm/widget.h>

    class MyWidget : public Gtk::Widget
    {
    public:
      MyWidget();
      virtual ~MyWidget();

    protected:

    #ifdef GLIBMM_DEFAULT_SIGNAL_HANDLERS_ENABLED
      //Overrides:
      virtual void on_size_request(Gtk::Requisition* requisition);
      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_expose_event(GdkEventExpose* event);
    #endif /* GLIBMM_DEFAULT_SIGNAL_HANDLERS_ENABLED */

      Glib::RefPtr<Gdk::Window> m_refGdkWindow;

      int m_scale;
    };

    #endif //GTKMM_CUSTOM_WIDGET_MYWIDGET_H

File: `examplewindow.h`

    #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::VBox m_VBox;
      MyWidget m_MyWidget;
      Gtk::HButtonBox m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc`

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : 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`

    #include <gtkmm/main.h>
    #include "examplewindow.h"

    int main(int argc, char *argv[])
    {
      Gtk::Main kit(argc, argv);

      ExampleWindow window;
      //Shows the window and returns when it is closed.
      Gtk::Main::run(window);

      return 0;
    }

File: `mywidget.cc`

    #include "mywidget.h"
    #include <gdkmm/drawable.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(false);

      //This shows the GType name, which must be used in the RC file.
      std::cout << "GType name: " << G_OBJECT_TYPE_NAME(gobj()) << std::endl;

      //This show 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 an RC
      //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,
            0,
            G_PARAM_READABLE) );

      gtk_rc_parse("custom_gtkrc");
    }

    MyWidget::~MyWidget()
    {
    }

    #ifdef GLIBMM_DEFAULT_SIGNAL_HANDLERS_ENABLED
    void MyWidget::on_size_request(Gtk::Requisition* requisition)
    {
      //Initialize the output parameter:
      *requisition = Gtk::Requisition();

      //Discover the total amount of minimum space needed by this widget.

      //Let's make this simple example widget always need 50 by 50:
      requisition->height = 50;
      requisition->width = 50;
    }

    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()
    {
      //Call base class:
      Gtk::Widget::on_realize();

      ensure_style();

      //Get the themed style from the RC file:
      get_style_property("example_scale", m_scale);
      std::cout << "m_scale (example_scale from the theme/rc-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_window() /* parent */, &attributes,
                GDK_WA_X | GDK_WA_Y);
        set_has_window();
        set_window(m_refGdkWindow);

        //set colors
        modify_bg(Gtk::STATE_NORMAL , Gdk::Color("red"));
        modify_fg(Gtk::STATE_NORMAL , Gdk::Color("blue"));

        //make the widget receive expose events
        m_refGdkWindow->set_user_data(gobj());
      }
    }

    void MyWidget::on_unrealize()
    {
      m_refGdkWindow.clear();

      //Call base class:
      Gtk::Widget::on_unrealize();
    }

    bool MyWidget::on_expose_event(GdkEventExpose* event)
    {
      if(m_refGdkWindow)
      {
        double scale_x = (double)get_allocation().get_width() / m_scale;
        double scale_y = (double)get_allocation().get_height() / m_scale;

        Cairo::RefPtr<Cairo::Context> cr = m_refGdkWindow->create_cairo_context();
        if(event)
        {
          // clip to the area that needs to be re-exposed so we don't draw any
          // more than we need to.
          cr->rectangle(event->area.x, event->area.y,
                  event->area.width, event->area.height);
          cr->clip();
        }

        // paint the background
        Gdk::Cairo::set_source_color(cr, get_style()->get_bg(Gtk::STATE_NORMAL));
        cr->paint();

        // draw the foreground
        Gdk::Cairo::set_source_color(cr, get_style()->get_fg(Gtk::STATE_NORMAL));
        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;
    }
    #endif /* GLIBMM_DEFAULT_SIGNAL_HANDLERS_ENABLED */

Chapter 26. Custom Widgets |  | Chapter 27. Recommended Techniques