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From: rcwlobe@cs.vu.nl (Reg Lobee)
Newsgroups: comp.sys.cbm
Subject: Re: Geos Questions
Message-ID: <4598@pinas.cs.vu.nl>
Date: 22 Nov 89 11:42:55 GMT
References: <10576@max.u.washington.edu|
Organization: V.U. Informatica, Amsterdam, the Netherlands
Lines: 33

In article <10576@max.u.washington.edu|, scott@max.u.washington.edu writes:
| In a previous post, some one mentioned that using a lightpen
| with GEOS was kind of useless because the pointer that follows
| the lightpen is very jerky, especially horizontally. Well, the
| cause of this jerkiness might be due to the screen display
| and not due to the computer. A lightpen work by reading the raster
| tracing of the screen as it refreshes the screen every 1/60th of
| a second. When a TV is used as the screen display, since it
| has a tunner, the display is prone to interferance from outside
| sources, thus preventing a clear display signal from the computer,
| which inturn might affect the proper reading of the raster by
| the light pen. So perhaps using a Monitor (an 80 columns monitor
| would be nice) would solve the problem.

An 80 colums monitor doesn't solve the problem (I use one). There is
no difference between a monitor and a tv. The jerkiness is the same.

| And also, cleaning the
| screen window before using the lightpen would also be of help.
| Remember the light pen is reading the necessary information
| from the screen, and a dirty screen clearly will inhibit a
| "clean" reading  :) , besides when was the last time you cleaned
| your screen.
| Oh ya... while you are at it, clean the head of the light pen
| too! It might be semi-blind.

Both are clean. The problem isn't one of the things mentioned above.
The VIC chip in the c64 just isn't capable of giving a steady
x-coordinate. Programs written for use with the lightpen always
average the x-coordinate so it is less jerky.

Reg Lobee,
rcwlobe@cs.vu.nl