XSetClipOrigin(dpy, buffer_gc, x,y);
XCopyArea(dpy, pm, buffer, buffer_gc, x, y, s, s, x, y);
/* copy buffer to screen (window) */
XSetClipOrigin(dpy, buffer_gc, x,y);
XCopyArea(dpy, pm, buffer, buffer_gc, x, y, s, s, x, y);
/* copy buffer to screen (window) */