Drawing lines is more interesting than just points, so here is a complete program:
File: myarea.h
#ifndef GTKMM_EXAMPLE_MYAREA_H #define GTKMM_EXAMPLE_MYAREA_H #include <gtkmm/drawingarea.h> #include <gdkmm/colormap.h> #include <gdkmm/window.h> class MyArea : public Gtk::DrawingArea { public: MyArea(); virtual ~MyArea(); protected: //Overridden default signal handlers: virtual void on_realize(); virtual bool on_expose_event(GdkEventExpose* e); Glib::RefPtr<Gdk::GC> gc_; Gdk::Color blue_, red_; }; #endif // GTKMM_EXAMPLE_MYAREA_H
File: main.cc
#include "myarea.h" #include <gtkmm/main.h> #include <gtkmm/window.h> int main(int argc, char** argv) { Gtk::Main kit(argc, argv); Gtk::Window win; win.set_title("DrawingArea"); MyArea area; win.add(area); area.show(); Gtk::Main::run(win); return 0; }
File: myarea.cc
#include "myarea.h" MyArea::MyArea() { // get_window() would return 0 because the Gdk::Window has not yet been realized // So we can only allocate the colors here - the rest will happen in on_realize(). Glib::RefPtr<Gdk::Colormap> colormap = get_default_colormap (); blue_ = Gdk::Color("blue"); red_ = Gdk::Color("red"); colormap->alloc_color(blue_); colormap->alloc_color(red_); } MyArea::~MyArea() { } void MyArea::on_realize() { // We need to call the base on_realize() Gtk::DrawingArea::on_realize(); // Now we can allocate any additional resources we need Glib::RefPtr<Gdk::Window> window = get_window(); gc_ = Gdk::GC::create(window); window->set_background(red_); window->clear(); gc_->set_foreground(blue_); } bool MyArea::on_expose_event(GdkEventExpose* /* event */) { // This is where we draw on the window Glib::RefPtr<Gdk::Window> window = get_window(); window->clear(); window->draw_line(gc_, 1, 1, 100, 100); return true; }
This program contains two classes. The first is a subclass of Gtk::DrawingArea
and contains an
on_expose_event
member function. This method is called whenever the image in the drawing
area needs to be redrawn.
The four additional arguments to draw_line()
(besides the graphics context as the first) are the
coordinates for the start and end of the line.
The TestWindow
class contains a drawing area. When it is created, it creates a drawing area
of 50 pixels across by 50 pixels tall. If the window is resized, the graphic drawn is kept in the top left corner of the
larger window. The drawing area is created with a default grey background.