Light Pens ...

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Jul 17 11:43:23 2001

I haven't given this matter a moment's thought for over three decades, but now
I'm curious how that CDC system figured out where I was pointing the light pen
when I selected a component from the menu, which was at the right margin of the
screen, and placed it on the screen. Those big tubes were storage types back
then and raster displays just didn't have the bandwidth to display what these
did.

Any thoughts?

Dick
----- Original Message -----
From: "Iggy Drougge" <optimus_at_canit.se>
To: "Sellam Ismail" <classiccmp_at_classiccmp.org>
Sent: Monday, July 16, 2001 6:46 PM
Subject: Re: Light Pens ...


> Sellam Ismail skrev:
>
> >On Mon, 16 Jul 2001, Tony Duell wrote:
>
> >> > So here's a trick question .. what happens when a person holds
> >> > a lightpen to a dark section of the screen. Is the lightpen
> >>
> >> Nothing happens (literally). The light pen never sees any light, so it
> >> can't send a signal to the video card, so the CRT controller can never
> >> report the position.
> >>
> >> > completely blind unless come pixel is lit up?
> >>
> >> Yes.
>
> >Ok, my mind is still blown. How does a light-pen drawing program work
> >then? (Or is a light-pen drawing program not possible?)
>
> The only light pen I've worked with is the Vectrex pen. And while a vector
> screen differs somewhat from a CRT (it's non-linear, which doesn't help
> decoding), the drawing program simply projected a dot on the screen, which was
> moved using the pen. IOW, the dot was registered by the pen, and placing the
> pen in any other spot on the screen didn't result in anything, one would have
> to move the dot around as a pointer, much like drag-and-drop.
> I suppose CRT programs worked the same way.
>
> --
> En ligne avec Thor 2.6a.
>
> I can't understand ANY current MICROS~1 product names!
> Are they now created with a random word generator?
> What is the intent behind the name "Visual Studio" for their compiler suite?
> What is "Interdev"?
> Why is the Virus Transfer Protocol product named "Outlook"?
> Grumpy Ol' Fred
>
>
Received on Tue Jul 17 2001 - 11:43:23 BST