Re: RFC: A generic pointer protocol

Keith Rohrer (
Fri, 15 Nov 1996 15:23:28 -0600

Alexandre Maret wrote:
> I followed the discussion about this "generic" protocol.
> It seems there is a lot of talk about non-generic choices
> (cf. pressure). Does the packet need to have a fixed length ?
> I don't think so. We could have a config struct that can
> describe a pointing device capabilities. For example,
> a pressurized-pen tablet (!) :
> The config :
> name,min value,max value
> {
> {"x",0,6000},
> {"y",0,4000},
> {"pressure",0,15}
> }
> When the application (which has to be enhanced a bit) start
> up, it just look if there is a "pressure" field in the config.
> If yes, then the *application* will know that the 3rd field is
> the pressure field, and the the value can be between 0 and 15.
The application needs to know which parts of the controller map to which
field anyway, right? So the protocol should define a standard for what
goes where; certain physical inputs may be represented in multiple
fields. Presumably for device-independence at the application level,
all ranged inputs would be scaled to the same thing.

So, for example, if all the inputs were 32-bit unsigned integers (big,
but not too nasty for alphas), you'd have button-down be -1 (i.e.
0xffffffff) and button-up be 0. Then apps checking for clicks could
just test for zero, while things which wanted pressure/velocity could
test the actual value.

You know, this is all starting to sound like a cross between a mouse
protocol and MIDI...


The priests and the friars/Behold me in dread
Because I still love you,/My love, and you're dead.
    ---Dead Can Dance, "I Am Stretched On Your Grave", based on King/S.
	O'Connor's rewrite of "The Unquiet Grave", trad. Irish folk.