Advertisement
ATARI Light Pen Operator's Manual
added to it. Try to draw on the screen in this mode. If you lift the
pen and press it to the screen elsewhere/ a line is drawn from the
last point occupied by the pen to the new position. If you wish to
prevent this interconnect line from being drawn/ press the pen to the
DRAW mode block before you press it into the drawing area again.
USER Mode
The top block in the drawing mode selector is the USER mode module.
Space in the program has been allocated for you to define your own
function. In the demonstration program/ it is defined at lines
6000-6900. Currently/ it retrieves the X and Y values of the pen and
does nothing with them. You may choose to add anything you wish to
this module/ such as plotting X and Y in a specific color.
If you have a disk drive/ you could have the user module display
a certain color in its menu block. When the pen is pressed there/
you could rotate the displayed color through the four available
colors. A certain color in this block would then specify one
of four disk files that can be used to load and save pictures.
Another possibility for the user module is using it to change the
hues and luminances of the picture. It can rotate through all
possible combinations/ or any one of many schemes you could invent.
With a little imagination/ you can find endless possibilities for
this module.
To use the user module/ the first change required to the program would
be a modification to line 1030/ which currently plots only a solid red
block in the user module space. (See Figure 6 for the program
listing. ) You may elect to plot any letter/ number/ or other figure in
this same space. The coordinates are: X between 144 and 159 inclusive/
and Y between 1 and 6 inclusive. Then in lines 6030-6900 you could do
something with the X and Y values received from <3ETP0S (maybe plot X/
Y).
The last line of the user module (line 6900) is GOTO 6020
(creating an infinite loop> because while you are in any one of the
DRAW modes/
you should stay there indefinitely until the DRAW mode is
changed. Don't worry about the tracking of the modes/ the moving of
the mode bars/ range checking/ or menu selection because they have
been handled by the rest of the program (study the other modes).
ATARI Light Pen Demonstration Program Cassette - 15
Advertisement
