#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include <X11/Xlib.h>


//-------------------------------------------------------------------------------------------------
//  gcc -shared -O3 -Wall -fPIC -Wl,-soname,get_screen -o get_screen.so get_screen.c -lX11
//-------------------------------------------------------------------------------------------------

GC createGC(Display* display, Window win){
  GC gc;
  int screen_num = DefaultScreen(display);
  unsigned long valuemask = 0;

  XGCValues values;

  values.subwindow_mode = IncludeInferiors;
  values.line_width = 2;
  valuemask = GCSubwindowMode | GCLineWidth;

  gc = XCreateGC(display, win, valuemask, &values);
  if (gc < 0) {
    fprintf(stderr, "XCreateGC: \n");
  }

  XSetForeground(display, gc, BlackPixel(display, screen_num));
  XSetBackground(display, gc, WhitePixel(display, screen_num));
  return gc;
}

void get_screen(const int dispNumber, const int xx,const int yy,const int W, const int H, /*out*/ unsigned char * data){
  Display *display;
  if (dispNumber == 1) {
    display = XOpenDisplay(":1.0");
    printf("Screenshoting display :1.0\n");
  }else{
    display = XOpenDisplay(":0.0");
    printf("Screenshoting display :0.0\n");
  }

  Window root = DefaultRootWindow(display);
  XImage *image = XGetImage(display,root, xx,yy, W,H, AllPlanes, ZPixmap);

  unsigned long red_mask   = image->red_mask;
  unsigned long green_mask = image->green_mask;
  unsigned long blue_mask  = image->blue_mask;
  int x, y;
  int ii = 0;
  for (y = 0; y < H; y++) {
    for (x = 0; x < W; x++) {
      unsigned long pixel = XGetPixel(image,x,y);
      unsigned char blue  = (pixel & blue_mask);
      unsigned char green = (pixel & green_mask) >> 8;
      unsigned char red   = (pixel & red_mask) >> 16;

      data[ii + 2] = blue;
      data[ii + 1] = green;
      data[ii + 0] = red;
      ii += 3;
    }
  }
  XDestroyImage(image);
  XDestroyWindow(display, root);
  XCloseDisplay(display);
}