bouncewm-kacper.c

#include <X11/Xlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>

// change this to your terminal emulator of choice
#define TERM_PATH "/usr/bin/termite"
#define TERM "termite"

// catch BadWindow errors that occur in the main loop
// when a window exits and ignore them
// you may consider this a hack, I don't :^)
int dummy_error_handler(Display *dpy, XErrorEvent *ev) {
	return 0;
}

int main() {
	Display *dpy;
	Window root, *children = NULL, tmp_root, tmp_parent;
	XWindowAttributes attr;
	XEvent ev;
	unsigned int nchildren = 0;
	int root_width, root_height;

	if(!(dpy = XOpenDisplay(0)))
		return 1;

	root = DefaultRootWindow(dpy);

	XGetWindowAttributes(dpy, root, &attr);
	root_width = attr.width;
	root_height = attr.height;

	pid_t term_pid = fork();
	if (!term_pid) {
		execl(TERM_PATH, TERM, NULL);
	}
	assert(term_pid != -1);

	sleep(1); // give the terminal some time to spawn a window

	int *move_x = NULL,
		*move_y = NULL;

	XSetErrorHandler(dummy_error_handler);

	while(1) {
		for (unsigned int i = 0; i < nchildren; i++) {
			if (children[i]) {
				if (XGetWindowAttributes(dpy, children[i], &attr) == BadWindow)
					continue;

				int new_x = attr.x + move_x[i],
					new_y = attr.y + move_y[i];

				XMoveWindow(dpy, children[i], new_x, new_y);

				if (new_x <= 0 || (new_x + attr.width) >= root_width)
					move_x[i] = -move_x[i];

				if (new_y <= 0 || (new_y + attr.height) >= root_height)
					move_y[i] = -move_y[i];
			}
		}

		if (children)
			XFree(children);

		unsigned int new_nchildren;
		// Xorg doesn't like us giving it NULLs for root_return and parent_return
		// (IMO it should, instead it segfaults in the library), even though we don't need them
		XQueryTree(dpy, root, &tmp_root, &tmp_parent, &children, &new_nchildren);

		if (new_nchildren > nchildren) {
			move_x = realloc(move_x, new_nchildren * sizeof(int));
			move_y = realloc(move_y, new_nchildren * sizeof(int));

			for (unsigned int i = nchildren; i < new_nchildren; i++) {
				move_x[i] = 1; // right
				move_y[i] = 1; // down
			}
		}

		nchildren = new_nchildren;

		int wstatus;
		if(waitpid(term_pid, &wstatus, WNOHANG))
			return wstatus; // terminal has exitted, pass on it's return status

		usleep(16000);
	}
}