Custom Widgets

#ifndef GTKMM_CUSTOM_WIDGET_MYWIDGET_H
#define GTKMM_CUSTOM_WIDGET_MYWIDGET_H

#include <gtkmm/widget.h>
#include <gtkmm/cssprovider.h>
#include <gtkmm/styleproperty.h>

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

protected:

  //Overrides:
  Gtk::SizeRequestMode get_request_mode_vfunc() const override;
  void get_preferred_width_vfunc(int& minimum_width, int& natural_width) const override;
  void get_preferred_height_for_width_vfunc(int width, int& minimum_height, int& natural_height) const  override;
  void get_preferred_height_vfunc(int& minimum_height, int& natural_height) const override;
  void get_preferred_width_for_height_vfunc(int height, int& minimum_width, int& natural_width) const override;
  void on_size_allocate(Gtk::Allocation& allocation) override;
  void on_map() override;
  void on_unmap() override;
  void on_realize() override;
  void on_unrealize() override;
  bool on_draw(const Cairo::RefPtr<Cairo::Context>& cr) override;

  //Signal handler:
  void on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section, const Glib::Error& error);

  Gtk::StyleProperty<int> m_scale_prop;
  Glib::RefPtr<Gdk::Window> m_refGdkWindow;
  Glib::RefPtr<Gtk::CssProvider> m_refCssProvider;

  int m_scale;
};

#endif //GTKMM_CUSTOM_WIDGET_MYWIDGET_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::Box m_VBox;
  MyWidget m_MyWidget;
  Gtk::ButtonBox m_ButtonBox;
  Gtk::Button m_Button_Quit;
};

#endif //GTKMM_EXAMPLEWINDOW_H

#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();
}

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

int main(int argc, char *argv[])
{
  auto app = Gtk::Application::create(argc, argv, "org.gtkmm.example");

  ExampleWindow window;

  //Shows the window and returns when it is closed.
  return app->run(window);
}

#include "mywidget.h"
#include <gdkmm/general.h>  // for cairo helper functions
#include <iostream>
//#include <gtk/gtkwidget.h> //For GTK_IS_WIDGET()
#include <cstring>

// The MyWidget class uses API which was added in gtkmm 3.15.3 (Gtk::CssProviderError,
// Gtk::CssProvider::signal_parsing_error() and Gtk::CssSection) and in gtkmm 3.15.2
// (Gtk::StyleProperty).

MyWidget::MyWidget() :
  //The GType name will actually be gtkmm__CustomObject_mywidget
  Glib::ObjectBase("mywidget"),
  Gtk::Widget(),
  //Install a style property so that an aspect of this widget may be themed
  //via a CSS style sheet file:
  m_scale_prop(*this, "example_scale", 500),
  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;

  m_refCssProvider = Gtk::CssProvider::create();
  auto refStyleContext = get_style_context();
  refStyleContext->add_provider(m_refCssProvider,
    GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
  m_refCssProvider->signal_parsing_error().connect(
    sigc::mem_fun(*this, &MyWidget::on_parsing_error));
    
  try
  {
    m_refCssProvider->load_from_path("custom_gtk.css");
  }
  catch(const Gtk::CssProviderError& ex)
  {
    std::cerr << "CssProviderError, Gtk::CssProvider::load_from_path() failed: "
              << ex.what() << std::endl;
  }
  catch(const Glib::Error& ex)
  {
    std::cerr << "Error, 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:
  m_scale = m_scale_prop.get_value();
  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);

    //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 Gtk::Allocation allocation = get_allocation();
  const double scale_x = (double)allocation.get_width() / m_scale;
  const double scale_y = (double)allocation.get_height() / m_scale;

  // paint the background
  get_style_context()->render_background(cr,
    allocation.get_x(), allocation.get_y(),
    allocation.get_width(), allocation.get_height());

  // 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;
}

void MyWidget::on_parsing_error(const Glib::RefPtr<const Gtk::CssSection>& section, const Glib::Error& error)
{
  std::cerr << "on_parsing_error(): " << error.what() << std::endl;
  if (section)
  {
    std::cerr << "  URI = " << section->get_file()->get_uri() << std::endl;
    std::cerr << "  start_line = " << section->get_start_line()+1
              << ", end_line = " << section->get_end_line()+1 << std::endl;
    std::cerr << "  start_position = " << section->get_start_position()
              << ", end_position = " << section->get_end_position() << std::endl;
  }
}

/* Example of a CSS style sheet with a custom style property.
 *
 * The name of the style property must have its canonical form, i.e. characters
 * other than ASCII letters, digits, and hyphens must be replaced by hyphens.
*/

* {
  /* -<widget class name>-<style property canonical name>: <value>; */
  -gtkmm__CustomObject_mywidget-example-scale: 920;
}

gtkmm__CustomObject_mywidget {
  background-color: rgb(255,0,0);
  color:            rgb(0,0,255);
}