Inquiry routine to determine the current window setting.
The values returned are world coordinates.
Arguments
X1 (output) : the x-coordinate of the bottom left corner
of the window.
X2 (output) : the x-coordinate of the top right corner
of the window.
Y1 (output) : the y-coordinate of the bottom left corner
of the window.
Y2 (output) : the y-coordinate of the top right corner
of the window.