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From: pilgrim@daimi.aau.dk (Jakob G}rdsted)
Newsgroups: comp.sys.amiga.hardware
Subject: drawingpad
Summary: drawingpad
Keywords: drawingpad
Message-ID: <1991Jan25.095710.6716@daimi.aau.dk>
Date: 25 Jan 91 09:57:10 GMT
Sender: pilgrim@daimi.aau.dk (Jakob G}rdsted)
Organization: DAIMI: Computer Science Department, Aarhus University, Denmark
Lines: 44

Before you read any further: This is just a silly idea I want to tell the
world about!

   The Amiga has got a nice port in which one plugs the mouse, and most
of the serious programs utilises this to move the pointer about. But
(especially in Painting programs, but also elsewhere) a mouse is only
one type of "userinterface", and it could be nice to use a drawing-
pad (these thingies with a plate and a pencil you move around), but
this would not be compatible with the mouse interface: The mouse works
by sending pulses for vertical and horisontal movement. Using a drawing
pad, you are able to lift the pen from the pad, and put it down elsewere
on it; here your coordinates are absolute. How could the mouse's inter-
face be adequate, to emulate lifting the pencil and putting it down else-
were ?  I always thought this was a bit impossible, but I have come up
with an idea ( which the rest of the world probably have known since 
stone age): It requires the drawing pad to be "intelligent" i.e. have
its own chips and therefore  powering, hopefully from the joystick
port(external powering is such a bad thing). I'm afraid it will be
expensive, but here we go:
   The drawing pad of course keeps track of the pen's absolute coordinates.
Whenever it is lifted, its coordinates are those it had when it left the
surface. In fact the pad should not keep track of where the pen is, but of
where the pad wants to tell the computer the pen is. This is quite like
the "draw continous curve with brush"function in Deluxe Paint - when
you  move the mouse too fast, you see that the computer in fact draw
straight lines between checkpoints. The pad should do the same. It should
sample a checkpoint, then emulate the pulses the mouse would send to
the computer if moving in a straight line to the new "destination", and
when it had updated the computer, sample another checkpoint
 (i.e. read where the pen is), and do another emulation of the mouse,
and so on.(this is why the board would need some chips, as I see it, it
must be able to do quite a lot of arithmetics)

   The solution used right now, I think, is a software interface that 
does the same thing(?) and works with most "wellwritten" programs like
DeluxePaint and such. 
   A  problem with this hardware solution is, that there will be a problem
with the alignment between the screen and the board. This could be solved
by a reset button on the board, allowing one to adjust it any time.
(you hold down the button, and you are free to move the pen around. When
you let go of the button, the cursor has Not moved).


Just a thought