Re: [newbie] How to plot to drawing_area

[Havoc Pennington <hp redhat com>]

On Sat, Feb 01, 2003 at 06:09:48PM -0300, Individual . . wrote: 
> I decided it would be great if I could learn how to plot an image to a 
> window, pixel by pixel. Getting the  image is no problem at all, since 
> I wrote a simple c++ class that uses libpng 
> (<http://pngwriter.sourceforge.net/>).
> The plotting part is what is holding me up.

Well, if you were just trying to get work done instead of trying to
learn, you could do:

 error = NULL;
 pixbuf = gdk_pixbuf_new_from_file ("foo.png", &error);
 if (error != NULL)
   {
     g_printerr ("error loading image: %s\n", error->message);
     g_error_free (error);
     exit (1);
   }
 image = gtk_image_new_from_pixbuf (pixbuf);

Even with a drawing area a pixbuf remains the way to go, but to draw
point by point you would do:

 GdkColor color;
 gc = gdk_gc_new (drawing_area->window);
 gdk_color_parse (&color, "blue"); /* or set color.red/color.blue/color.green */
 gdk_gc_set_rgb_fg_color (gc, &color);
 
 gdk_draw_point (drawing_area->window, gc, x, y);

But this is far too slow for drawing a whole image.

See gtk-demo, it has examples of both of these things or similar to
them, I think.

Havoc