Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!overload!dillon
From: dillon@overload.Berkeley.CA.US (Matthew Dillon)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 3D stuff & quick line drawing
Message-ID: <dillon.6817@overload.Berkeley.CA.US>
Date: 22 Apr 91 03:23:28 GMT
References: <1991Apr21.081925.4722@lynx.CS.ORST.EDU>
Organization: Not an Organization
Lines: 46

In article <1991Apr21.081925.4722@lynx.CS.ORST.EDU> divineg@prism.CS.ORST.EDU writes:
>
>	Here's my situation:
>
>I've coded and coded and coded and finally found a way to crudely rotate
>3 dimensional objects ... now all of you wizards out there, what's the
>quickest way to draw a line?  I'd like to do it with the Blitter (I can
>use the processer to calculate while I draw lines) or is it better to use
>the 68'?  By the way, I'm using C & asm (pretty original, huh?).
>	Please post your responses, I'm interested in what kind of
>discussion follows.....
>
>Yenivid Edalg 8^)
>(E-Mail me at divineg@prism.cs.orst.edu)

    Hmm.  Well, 3D is actually easy if you use standard matrix theory,
    any good graphics book will have it.  It is all extremely general
    and you can do practically *anything* with it (4x4 matrices).  Once
    you get it working in the general sense you can optimize the *ell out
    of the code, remove whole chunks of calculations that do not apply.

    Word to the wise on 3D:  stick with vectors instead of polar
    coordinates if you want to easily code arbitrary view points &
    movement.  You also avoid arctan completely with vectors and sin/cos
    are not only relegated to table lookups, you can precalculate most of
    what you need once per frame instead of for each object.  The problem
    with polar coordinates is that they are not uniform -- for example, the
    direction represented by phi=+/-90 degrees causes theta to go wild
    (theta can become anything without effecting the direction).

    Back to line drawing:  It has been shown that the processor can
    draw short lines much faster than the blitter can due to blitter
    setup overhead.  I believe the breakoff point is somewhere around
    150 pixels.  I'd stick with standard Move/Draw in a modular routine
    until you get to the point where you really need to optimize, unless
    you have already written optimized line drawing routines, in which
    case you just use those.

					-Matt

--

    Matthew Dillon	    dillon@Overload.Berkeley.CA.US
    891 Regal Rd.	    uunet.uu.net!overload!dillon
    Berkeley, Ca. 94708
    USA