import ctypes as c
from PIL import Image

def capture(display_name,dest,window=None):
 x=c.CDLL('libX11.so.6')
 x.XOpenDisplay.argtypes=[c.c_char_p];x.XOpenDisplay.restype=c.c_void_p
 x.XDefaultRootWindow.argtypes=[c.c_void_p];x.XDefaultRootWindow.restype=c.c_ulong
 x.XGetGeometry.argtypes=[c.c_void_p,c.c_ulong,c.POINTER(c.c_ulong),c.POINTER(c.c_int),c.POINTER(c.c_int),c.POINTER(c.c_uint),c.POINTER(c.c_uint),c.POINTER(c.c_uint),c.POINTER(c.c_uint)]
 class XI(c.Structure):
  _fields_=[('width',c.c_int),('height',c.c_int),('xoffset',c.c_int),('format',c.c_int),('data',c.c_void_p),('byte_order',c.c_int),('bitmap_unit',c.c_int),('bitmap_bit_order',c.c_int),('bitmap_pad',c.c_int),('depth',c.c_int),('bytes_per_line',c.c_int),('bits_per_pixel',c.c_int),('red_mask',c.c_ulong),('green_mask',c.c_ulong),('blue_mask',c.c_ulong)]
 x.XGetImage.argtypes=[c.c_void_p,c.c_ulong,c.c_int,c.c_int,c.c_uint,c.c_uint,c.c_ulong,c.c_int];x.XGetImage.restype=c.POINTER(XI)
 x.XDestroyImage.argtypes=[c.POINTER(XI)];x.XCloseDisplay.argtypes=[c.c_void_p]
 d=x.XOpenDisplay(display_name.encode())
 if not d:raise RuntimeError('Cannot open verified private display')
 root=window or x.XDefaultRootWindow(d);r=c.c_ulong();xx=c.c_int();yy=c.c_int();w=c.c_uint();h=c.c_uint();bw=c.c_uint();depth=c.c_uint()
 if not x.XGetGeometry(d,root,c.byref(r),c.byref(xx),c.byref(yy),c.byref(w),c.byref(h),c.byref(bw),c.byref(depth)):raise RuntimeError('No root geometry')
 im=x.XGetImage(d,root,0,0,w.value,h.value,c.c_ulong(-1).value,2)
 if not im:raise RuntimeError('No private screenshot')
 v=im.contents
 assert v.bits_per_pixel==32 and v.byte_order==0 and (v.red_mask,v.green_mask,v.blue_mask)==(0xff0000,0xff00,0xff)
 Image.frombytes('RGB',(w.value,h.value),c.string_at(v.data,v.bytes_per_line*h.value),'raw','BGRX',v.bytes_per_line).save(dest)
 x.XDestroyImage(im);x.XCloseDisplay(d)