Path: utzoo!attcan!uunet!munnari.oz.au!uhccux!virtue!math1205
From: math1205@waikato.ac.nz
Newsgroups: comp.graphics
Subject: Animation Speed
Message-ID: <675.266fc62b@waikato.ac.nz>
Date: 8 Jun 90 03:37:15 GMT
Organization: University of Waikato, Hamilton, New Zealand
Lines: 30

I have been experimenting with sprite animation recently and came up
with an unexpected result which I can not explain.
I'm using an Atari ST with a 50Hz colour monitor to animate a sprite 
moving back and forth across the screen. The program was a simple loop 
which did the following:

Drawsprite(x,y)  VerticalSync()  Undrawsprite() Update_Pos(x)

The sprite used was a small 8x8 pixel ball and the x-increment used is
16 pixels. This version worked nicely and gave a very smoothly moving ball 
displayed at a refresh rate of 50Hz.

The next version should also display a smoothly moving ball which is refreshed
at the slower rate of 25Hz via:

Drawsprite(x,y) VerticalSync() VerticalSync() Undrawsprite() Update_Pos(x)

I seemed to recall from computer graphics literature that a refresh rate of
20 Hz should be sufficient to give the impression of animation.
What I actually saw was two very faint balls adjacent to each other 
travelling across the screen.
Even when the x-increment is reduced to 1 pixel the same effect is 
noticeable as a blurring of the image.

Is the reason for this ghosting effect a too slow refresh rate? And if so, 
what is the minimum refresh rate to produce smooth animation?
Replies please !

Wayne Schou
MATH1205@waikato.ac.nz