#include <stdio.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>

#include <sys/ipc.h>
#include <sys/shm.h>
#include <X11/extensions/XShm.h>

void slop(Window *window, unsigned int *w, unsigned int *h)
{
	FILE *slop;
	char out[256];

	slop = popen("/usr/bin/slop -f '%i,%w,%h'", "r");
	fread(out, sizeof(out), 1, slop);
	pclose(slop);

	sscanf(out, "%lu,%u,%u", window, w, h);
}

int main(int argc, char **argv)
{
	Display *display;
	Window window_in, window_out;
	GC gc;
	XEvent ev;
	XWindowAttributes attrs;
	XShmSegmentInfo shminfo;
	XImage *image;
	unsigned int w,h;

	slop(&window_in, &w, &h);

	display = XOpenDisplay(NULL);
	gc = DefaultGC(display, DefaultScreen(display));

	window_out = XCreateSimpleWindow(display, DefaultRootWindow(display), 0, 0, w, h, 0, 0, 0);
	XSelectInput(display, window_out, StructureNotifyMask | ButtonPressMask);
	XMapWindow(display, window_out);

	XNextEvent(display, &ev); // wait for window to be mapped

	do {
		XGrabServer(display);
		XGetWindowAttributes(display, window_in, &attrs);

		// doesn't have the bug
		//image = XGetImage(display, window_in, 0, 0, attrs.width, attrs.height, 0xffffffff, ZPixmap);

		// has the bug
		image = XShmCreateImage(display, attrs.visual, attrs.depth, ZPixmap, NULL, &shminfo, attrs.width, attrs.height);
		shminfo.shmid = shmget(IPC_PRIVATE, image->bytes_per_line * image->height, IPC_CREAT|0777);
		shminfo.shmaddr = image->data = shmat(shminfo.shmid, 0, 0);
		shminfo.readOnly = False;
		XShmAttach(display, &shminfo);
		XShmGetImage(display, window_in, image, 0, 0, AllPlanes);

		XUngrabServer(display);
		XPutImage(display, window_out, gc, image, 0, 0, 0, 0, attrs.width, attrs.height);

		XShmDetach(display, &shminfo);
		XDestroyImage(image);
		shmdt(shminfo.shmaddr);
		shmctl(shminfo.shmid, IPC_RMID, 0);

		XNextEvent(display, &ev);
	} while (ev.type != ButtonPress);

	return 0;
}