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From: haitex@pnet01.cts.com (Wade Bickel)
Newsgroups: comp.sys.amiga
Subject: Questions about 3-D glasses.
Message-ID: <2444@crash.cts.com>
Date: 29 Jan 88 12:18:43 GMT
Sender: news@crash.cts.com
Organization: People-Net [pnet01], El Cajon CA
Lines: 110


In a letter crash!eniac.seas.upenn.edu!ranjit (Ranjit Bhatnagar) writes me:

> A couple of questions about your 3d package...
> 
> 	- any estimates on approximate cost of package w/one set of glasses?
> 

	       I'm not really sure what the price will be but they should 
	    be under $100 with software.  How much under will depend partly
            on how U.S. customs classifies them.
	    
> 	- why no intuition or multitasking?  Speed isn't really a factor
> here, because the fastest possible swap between eyes is 30 swaps/second.
> I'm no expert, but I can think of several ways to do this under multitasking
> and intuition that at least seem feasible.  For instance...
> 
		Essentially, speed is the factor.  In order to create reason-
	   able 3-D the highest possible switching rate must be maintained.
	   On most (but not all) Amiga's this is constrained to 60 switches
	   per second.  Since Intuition's screen update options all require
	   re-merging of the copper lists, they are out of the question be-
	   cause they take too long.
	   
	   	I have experimented with finding the ViewPort intuition is
	   using and using it for my LoadView() call to no avail.  It may
	   be possible to get around this, but intuition doesn't have enough
	   to offer to make it worthwhile.  Needed intuition functions are
	   always available by opening a window underneath a graphics screen.

> 	+ install a VBI interrupt, modeled after the one used on interlace
> 	screens, which changes the bitmap location of your stereo screen
> 	at every frame, and also (probably writing straight to hardware,
> 	for speed - I concede this intuition-stopper) sends the "change-eyes"
> 	signal to the glasses.
> 

		Actually, I have a little bit more complicated system sitting
	on the VBlank chain.  I also tried using the copper to generate the
	interrupt with some strange results (though it generally worked).
	Basically you have the right idea.  As noted above, intuition's
	screen re-draw functions are indeed too slow.	

	     Multi-tasking is stopped here because if another task tries to
	take the screen this server (VBlank) will try to take it back.  I
	think I see a work around to this problem.  I sent C= and a few others
	a suggestion that an addition be made to the Task Block structure
	to eliminate this problem but have gotten no response.

> 	+ use a normal interlace screen, and write left-eye pictures on even
> 	lines and right-eye pictures on odd lines.  This has the two dis-
> 	advantages of not being able to use standard line/area calls to
> 	draw into the screen, and when you pull down this screen to expose
> 	the workbench, the workbench will be interlaced too - causing
> 	ugly effects if the user keeps the glasses on.  The first trick
> 	has the nice property that you can pull down the screen and see
> 	the workbench with both eyes (unless it's an interlaced workbench).
> 

	      This is out of the question for a number of reasons (some of
	 which you point out.  In particular, it messes up the vertical 
	 orientation of things just a bit, and of course the drawing functions
	 are non-functional.

> 	+ do whatever the people who make ANIM and MOVIE players do.  They
> 	reach 30 frames/sec easily, and compatibly, while doing horrendous
> 	huge decompression calculations too.
> 

	       What do they do?  I'm always open to suggestions.

> Though I am quite interested in the use of LCD glasses for 3D, I would 
> not buy a package with these limitations, and I suspect that many others
> 
> would feel the same way - preferring to wait for a competitor to do the
> same thing with multi-tasking and intuition compatibility.  Unless it can
> be shown to be impossible, which I doubt.
> 

	There comes a point of diminishing returns for trying to support
these features.  It is my hope that I will be able to perform a work around
for the multi-tasking problem that will be almost transparent, or maybe
someone will offer a solution I've not seen?

	I hope people can live without intuition as it carries too much 
inappropriate overhead to really use.   I've seen a suprising number of
graphics aplications and games which do not use intuition.

> By the way, it would be nice if you could post this to comp.sys.amiga,
> if what I said isn't completely stupid, so I can hear what others think.
> (I can't post from here.)
> 

	OK.  I'm posting it with my responses to avoid redundancy.
	
	
	
						Thanks for your intrest,
						
						
							     Wade W. Bickel
							     Haitex Resources.

						
	


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