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From: jdb@reef.cis.ufl.edu (Brian K. W. Hook)
Newsgroups: rec.games.programmer,comp.os.msdos.programmer
Subject: 3D int/float optimizations stuff
Message-ID: <28002@uflorida.cis.ufl.EDU>
Date: 12 Apr 91 23:14:07 GMT
Sender: news@uflorida.cis.ufl.EDU
Organization: UF CIS Dept.
Lines: 68

Thanks to everyone who helped with the optimizations.  For those
interested, I am posting the results of each optimization followed by the
final source code.

Summary:  WOW!

First pass:    	21.86 seconds
Optimizations: none (this means all doubles/floats)

Second pass:   	21.48 seconds
Optimizations:  converted functions to pass pointers to objects instead of
                copies of objects

Third pass:	13.40 seconds(!)
Optimizations:	converted most of the calculations to fixed point integer
		calculations versus floating point

Fourth pass:	13.35 seconds
Optimizations:	converted "tmp" variable from long to int

Fifth pass:	12.46 seconds
Optimizations:	converted global variable from double to int

Last pass:	12.20 seconds
Optimizations:	converted _yaw, _roll, and _pitch to ints from doubles

I am sure that a couple of optimizations can still be done, most obviously
those bit shifts (although I really doubt they matter much).  I am not sure
how accurate these calculations are, but I do know that they don't distort
when displaying wireframe images which is all I care about.  I chose to
shift by 10 completely arbitrarily.

If you have any suggestions, please post or mail.

This is the actual function.  It is based on pseudo code from Lee Adam's "
Hi Performance Interactive Graphics in C" but is a pretty crappy book
otherwise.

/*

WX, WY, and WY:   World coordinates of object (relative to object's center)
MX, MY, and MZ:	  Distance object is from viewpoint
*DX, *DY:	  Final display coordinates

*/

void Calc3D ( int WX, int WY, int WZ, int MX, int MY, int MZ, int *DX, int
		*DY)
{
int tmp;
long xa, ya, za;   // Temp variables

   WX=-WX;
   xa=(_yawCosFactor*WX-_yawSinFactor*WZ)>>10;
   za=(_yawSinFactor*WX-_yawCosFactor*WZ)>>10;
   WX=(_rollCosFactor*xa+_rollSinFactor*WY)>>10;
   ya=(_rollCosFactor*WY-_rollSinFactor*xa)>>10;
   WZ=(_pitchCosFactor*za-_pitchSinFactor*ya)>>10;
   WY=(_pitchSinFactor*za+_pitchCosFactor*ya)>>10;
   WX+=MX;
   WY+=MY;
   WZ+=MZ;
   if (WZ==0)
      WZ=-1;
   tmp=AngularPerspFactor/WZ;
   *DX=tmp*WX+400;
   *DY=tmp*WY+300;
}