Get pixel's color in C++, Linux

Question

Hello,

I'm looking for a possibility to get the color of a pixel with given screen coordinates (x,y) in c++ / Linux? Maybe something similarly like getPixel() in Windows. I spent the whole day to find sth but without any success.

Thanks, Stefan

Answer 1

See various different techniques posted at http://ubuntuforums.org/showthread.php?t=715256

Answer 2

Assuming you mean using C and GTK the answer can be using:

gdk_get_default_root_window()

And

GdkPixbuf*  gdk_pixbuf_get_from_drawable    (GdkPixbuf *dest,
                                             GdkDrawable *src,
                                             GdkColormap *cmap,
                                             int src_x,
                                             int src_y,
                                             int dest_x,
                                             int dest_y,
                                             int width,
                                             int height);

EDIT: sample c++ code using Gdkmm (note that this is just a sample that assume an RGB color space, you should check the colorspace of the drawable before giving a meaning to the raw bytes).

#include <iostream>
#include <gtkmm.h>
#include <gdkmm.h>

int main(int argc, char* argv[])
{
  Gtk::Main kit(argc, argv);
  if(argc != 3) { std::cerr << argv[0] << " x y" << std::endl; return 1;}
  int x = atoi(argv[1]);
  int y = atoi(argv[2]);
  Glib::RefPtr<Gdk::Screen> screen = Gdk::Screen::get_default();
  Glib::RefPtr<Gdk::Drawable> win = screen->get_root_window();
  Glib::RefPtr<Gdk::Pixbuf> pb = Gdk::Pixbuf::create(win, x, y, 1, 1);
  unsigned char* rgb = pb->get_pixels();
  std::cerr << (int)rgb[0] << ", " << (int)rgb[1] << ", " << (int)rgb[2] << std::endl;
  return 0;
}

Answer 3

How to compile it?