From: lasner@watsun.cc.columbia.edu (Charles Lasner)
Subject: Re: QUESTION: What was the 1st computer game?
Reply-To: lasner@watsun.cc.columbia.edu (Charles Lasner)
Organization: Columbia University
Date: Wed, 18 Nov 1992 12:31:54 GMT

In article <13959@pogo.wv.tek.com> kevind@pogo.wv.tek.com (Kevin Draz) writes:
>In article <1992Nov14.002401.10531@news.columbia.edu> lasner@watsun.cc.columbia.edu (Charles Lasner) writes:
>>>
>>>The Tektronix 405x series desktop micros (6800 based?) had a nice
>>>spacewar type game (I've never seen the real spacewar so the similarity
>>>is based on my interpretation of other people's description - several
>>>levels of indirection there).  You didn't need to turn off the
>>>persistence to make a usable game since the initial drawing was so much
>>>brighter than the stored image.  The ships were just redrawn
>>>continuously, making a bright image, and the stored afterimages left a
>>>trail behind each ship.  The screen got a little cluttered after while,
>>>but it wasn't distracting or anything. 
>>>
>>>Sam
>>A crude approximation.
>>
>>Many people have discussed the shortcomings of video adaptations of games
>>trivially written for D-A and scopes.  The tradeoffs are large, and
>>all subtleties are destroyed.
>>
>>Video games move objects by display lists which have objects deleted, or
>>possibly you use XOR logic to display planes to erase the object and then
>>redraw a similar one at another position.  Any approach like this is crude
>>compared to the truly random access X-Y coordinate system of an analog
>>scope.
>
>
>Charles, the 4050 computers essentialy used storage scopes as displays, and
>were addressed through DA converters.  In fact, Tektronix developed DVST
>(direct-view storage tubes) for 'scopes, and later used them as displays for
>computers, because they could (and did) offer resolution up to 12 bits X & Y
>without the need for the attendant refresh RAM. 
>
>Vectors, ovals, etc. were drawn from point-to-point (directed beam, not
>rastered), and using low-pass filters, were truly analog in appearance,
>especially considering there were only 11" diagonally on which to map all
>these bits of resolution.
>
>In fact, you could recreate any image that a 'scope could display on a DVST
>computer (though not necessarily in realtime, due to CPU limits those days).
>But for a game with limited graphics requirements, as compared to real time
>scope waveforms, the machine could do it.
>
>I never saw the original spacewar, so I can't refute your label of this
>implementation as a "crude approximation", but if so, it certainly isn't for
>the reason of display capabilities.
>
>KD

Sorry to burst your bubble, but it is precisely for reason of display
capabilities that it doesn't work.  Not for the same reason as the video
hardware inadequacy, I agree there are no "jaggies" here (the two methods do
share the idea of outputting more resolution than can be seen, so no human
observer could ever claim a curve was anything other than a curve), but
because of the storage hardware, and the "overkill" of the device talking
to it.

The reason spaceware (the actual game) does what it does is because the
tube is *not* a storage tube.

It is necessary that the D-A interfaces be direct access to the screen, and
can refresh the screen at a program-controlled (and varying) rate.  The
use of "too much hardware" inhibits this.  The rocket ships have flames, not
"vapor trails" (which you can see if you deliberately use a longer-persistance
'scope tube), but a simulated gaseous flame that sparkles and flits about
even when the ship is not otherwise moving.  It's quite realistic, and
some of the same effect is imparted to the sun display as well.

Thus, were the program to refresh all points at a constant rate, it could
be argued that a vector graphics processor could also do spacewar, but
since this isn't the case, vector graphics versions don't look like spacewar.
Storage tube versions look even less like spacewar due to the distortion
introduced by the storage time which gives it a "flat" look.  There have
been other storage tube interfaces to machines such as the PDP-8; DEC sold
one with a 613 attached, and there were games for it, etc., but they
all lacked the "dynamic" look of spacewar, which was ported to all sorts
of hardware with one common design aspect: direct aspect D-A to the scope
demanding program refresh, and the ability to accomplish it at a program-
controlled rate.

cjl







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