Re: Getting the color of a pixel

[Owen Taylor <otaylor redhat com>]

Bryan Brown <bbrown saltmine radix net> writes:

> How does one get the color of a pixel in a drawing area or a pixmap using
> gtk 1.2 on a Linux box?
>
> I'm successfully drawing lines and points in different colors, but I also
> need to be able to get the color of a given point that's already been
> drawn in another routine.

I'd generally try to avoid doing this, it's going to be inefficient
and not very reliable. (Certainly don't do this for a window; the
point might be obscured by another window or offscreen. It's
a little better for a pixmap.)

For GTK+-1.2 it's also not possible to do without dropping down
to Xlib. GTK+-2.0 adds gdk_colormap_query_color() which you can
use like:

====
  image = gdk_drawable_get_image (root_window, x_root, y_root, 1, 1);
  pixel = gdk_image_get_pixel (image, 0, 0);
  g_object_unref (image);

  gdk_colormap_query_color (colormap, pixel, &color);
===

(Code snippet from gtkcolorsel.c's color dropper ... that's about
the only case I would suggest it.)

Regards,
                                        Owen