🚀 go-pugleaf

In article <1992Dec19.221442.3741@news2.cis.umn.edu> toddl@county.lmt.mn.org (Todd Lehman) writes:
>In article <1992Dec19.190258.15117@midway.uchicago.edu> greg@dent.uchicago.edu (Greg Kuperberg) writes:
>>Now for some specifics.  The eye and the visual cortex integrates
>>separate images into continuous motion if the images appear at a rate
>>faster than 5 or 10 times per second or so.  15 or more frames per
>>second looks good, and it is a waste of CPU time to have more than 30
>>redraws per second.
>
>No matter how perfectly your page flipping / double buffering works, no
>matter how fast your sprites are painted into video memory, if you move an
>object n pixels every 2 video cycles, there will be a ghost image trailing
>behind by n/2 pixels.  (Don't believe it?  Try it!) 
>
>Has anyone else observed this ghosting effect?  Does anyone know what is
>the cause?  I believe it to be an optical illusion, since the ghosting is
>not there when your eyes remain fixed.

I have noticed it, just yesterday when it started taking more than one tick
to do my pre-draw calculations, and it ended up drawing every other tick
(where a tick is one monitor refresh).  I thought something was wrong with
my drawing routines at first, but then realized that was impossible.  I
believe it's an optical illusion, since I have proved (in my head) that the
old sprite and the new one can not be on the screen at the same time.  I
don't know what you mean by 'your eyes remain fixed' but the ghosting is
always there for me.  I recently took a computer science graduate level
course in vision, not that that means anything, but my somewhat-educated
intuition tells me that it's definitely an optical illusion.

But more importantly, is there any way to reduce or (gasp!) eliminate the
effect?  It sure would be nice to only have to do 30 frames per second....

>It's the same kind of effect you
>see when 24 f.p.s. movies are converted to 30 f.p.s. video cassette format
>by doubling up every 5th frame.  (Ever wonder why movies on TV look kind-of
>jerky, but live video such as talk shows and soaps look smooth?)

I've never noticed this effect.  Are you sure it isn't just you? :)

Later,

Mike.
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Michael A. Kelly                                               Senior Partner
mkelly@cs.uoregon.edu                                      High Risk Ventures
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