Lightpen Functions for C02 Programs

This module contains a constant and function for reading lightpens on 
systems that support them.

The constants and assembly code vary by system, so when invoking the 
cross-compilers, the command line option -s must be used to ensure that
the correct header files are included.

At the beginning of the program use the directives

  #include <lgtpen.h02>

The following constants are defined:

  #LGTPNS       Light pen status. If loght pen support is available,
                this will be 255 (true), otherwise, it will be 0 (false).

The following function is defined:

  h,v,t = lgtpen();     Returns the state of the lightpen ot lightgun.

                        This function returns three values: the first
                        is the horizontal position on the screen, the 
                        second is the vertical position on screen, and
                        the third is the state of the button or trigger
                        (255 if pressed, otherwise 0).
                        
                        Note: The position returned by this function is
                        based on the position of the raster beam and does
                        not directly correspond to pixel coordinates. 
                        Therefore, some sort of calibration and conversion
                        will be necessary when using a light pen.

Note: This library has no external dependencies.
