#include <gtk/gtk.h>
#include <math.h>
#include <cairo.h>
 
#define WIDTH   640
#define HEIGHT  480
 
#define ZOOM_X  100.0
#define ZOOM_Y  100.0
 
 
gfloat f (gfloat x)
{
	return 0.03 * pow (x, 3);
}
 
static gboolean
on_expose_event (GtkWidget *widget, GdkEventExpose *event, gpointer user_data)
{
	cairo_t *cr = gdk_cairo_create (widget->window);
	GdkRectangle da;            /* Dimensions de la GtkDrawingArea */
	gdouble dx = 5.0, dy = 5.0; /* Nombre de pixels entre chaque point calculé */
	gdouble i, clip_x1 = 0.0, clip_y1 = 0.0, clip_x2 = 0.0, clip_y2 = 0.0;
	gint unused = 0;
 
	/* On définit la zone de clipping, cela correspond à la zone à 
	 * raffraîchir. En ne dessinant que le strict nécessaire, on dessinera 
	 * plus rapidement */
	cairo_rectangle (cr, 
			event->area.x, 
			event->area.y, 
			event->area.width, 
			event->area.height);
	cairo_clip (cr);
 
	/* On détermine les dimensions de la GtkDrawingArea */
	gdk_window_get_geometry (widget->window, 
			&da.x, 
			&da.y, 
			&da.width, 
			&da.height, 
			&unused);
 
	/* On dessine un fond noir */
	cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
	cairo_paint (cr);
 
	/* On change la matrice de transformation. C'est comme un changement 
	 * de repère en mathématiques. On centre d'abord l'origine du repère.
	 * Ensuite on change son échelle */
	cairo_translate (cr, da.width / 2, da.height / 2);
	cairo_scale (cr, ZOOM_X, -ZOOM_Y);  
 
	/* On détermine les points à calculer (c'est à dire ceux se trouvant 
	 * dans la zone de clipping) */
	cairo_device_to_user_distance (cr, &dx, &dy);
	cairo_clip_extents (cr, &clip_x1, &clip_y1, &clip_x2, &clip_y2);
	cairo_set_line_width (cr, dx);
 
	/* On dessine les axes */
	cairo_set_source_rgb (cr, 0.0, 1.0, 0.0);
	cairo_move_to (cr, clip_x1, 0.0);
	cairo_line_to (cr, clip_x2, 0.0);
	cairo_move_to (cr, 0.0, clip_y1);
	cairo_line_to (cr, 0.0, clip_y2);
	cairo_stroke (cr);
 
	/* On rajoute les points de la coube en les reliants par une droite */
	for (i = clip_x1; i < clip_x2; i += dx)
		cairo_line_to (cr, i, f (i));
 
	/* On dessine la courbe */
	cairo_set_source_rgba (cr, 1, 0.2, 0.2, 0.6);
	cairo_stroke (cr);
 
	cairo_destroy (cr);
	return FALSE;
}
 
 
int
main (int argc, char **argv)
{
	GtkWidget *window;
	GtkWidget *da;
 
	gtk_init (&argc, &argv);
 
	window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
	gtk_window_set_default_size (GTK_WINDOW (window), WIDTH, HEIGHT);
	gtk_window_set_title (GTK_WINDOW (window), "Affichage de courbe");
	g_signal_connect (G_OBJECT (window), "delete-event", gtk_main_quit, NULL);
 
	da = gtk_drawing_area_new ();
	gtk_container_add (GTK_CONTAINER (window), da);
 
	g_signal_connect (G_OBJECT (da), 
			"expose-event", 
			G_CALLBACK (on_expose_event), 
			NULL);
 
	gtk_widget_show_all (window);
	gtk_main ();
 
	return 0;
}