VFillImageRectangle - fills a rectangle in the image window.
  VFillImageRectangle(win, xloc, yloc, width, height, value)
  Window win;
  int xloc, yloc;
  int width, height;
  unsigned long value;
  VFillImageRectangle fills a specified rectangle in the image window or one
of its subwindows with the specified pixel value. If the image is partially 
out of the window boundary, VFillImageRectangle clips the image, displays the 
clipped image in the window, and returns an error code.
Return Value
  0 - work successfully.
  6 - invalid window ID.
  240 - image displayed is out of window boundary.
  win - the image window ID or one of its subwindows' ID.
  xloc, yloc - specifies x and y coordinates of the upper left corner of the
        rectangle, relative to the origin of the specified window.
  value - specifies the pixel value to fill the image window.
Side Effects
Entry Conditions
  If the value xloc, yloc, width, height, or  value is not valid, or
VCreateColormap is not called earlier, or the rectangle to be filled is 
totally out of the specified window boundary, VFillImageRectangle prints an 
error message to the standard error stream, produces a core dump file and 
exits from the current process.
Related Functions
VFillOverlayRectangle, VClearWindow, VGetFreeColorcells.