Path: chuka.playstation.co.uk!scea!peter_alau@playstation.sony.com
From: "dr Z" <gsauve@sie.qc.ca>
Newsgroups: scee.yaroze.beginners
Subject: Re: Plotting 2D Boxes in a 3D World (+ faster code hint!)
Date: 15 May 1998 04:04:48 GMT
Organization: SCEA News Server
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This is a little off topic but now on Pentium and on Power PC processors,
using Y*320 instead of Y<<8 + Y<<6 is faster because of the cost of
stalling the processor and the less cycles used by the multiplication
instruction. And I agree that there is a lot of room for optimisation these
days.

Now, on a more related topic, could it be more faster and memory efficient
to use GsLines instead of sprites or GsBOXFs. A line uses less packets in
the WorkBase and the GPU doesn't have to do a look-up in VRAM. You could
use a GsGLINE with the semi-transparency rate set to 1xback + 1xforward and
a width of 2 to 4 to simulate the blur of a fast moving stars.

something like:

GsGLINE TheLine;
 
TheLine.attribute = (1<<30)+(1<<28);
TheLine.x0 = 0;
TheLine.y0 = random(240);
TheLine.x1 = 4;
TheLine.y1 = TheLine.y0;
TheLine.r0 = TheLine.g0 = TheLine.b0 = 0xFF;
TheLine.r1 = TheLine.g1= TheLine.b1 = 0;

To speed things up a little bit, you could put the GsLINE ( or other
structure ) used many times in the Data-Cache of the CPU so it would be
faster to copy it in the OT.

Ex:

// somewhere in the program

#define MaxStars 500

typedef struct Star{
    short X,Y;
}Star;

Star Stars[MaxStars];

//initialisation of the Star array
register u_long i;
for (i=0;i<MaxStars;i++)
    {
    Stars[i].X = random(MaxXRes );
    Stars[i].Y = random(MaxYRes );
    }


// in the drawing proc
register GsGLINE  *TheLine = (GsGLINE*)0x1F800000; // Map to the logical
memory space of the D-Cache
register u_long i;
register u_short StarsPri = 16383;
register Star *TheStar;
 
TheLine->attribute = (1<<30)+(1<<28);
TheLine->r0 = TheLine->g0 = TheLine->b0 = 0xFF;
TheLine->r1 = TheLine->g1= TheLine->b1 = 0;

// the drawing loop should look like this
for (i=0;i<MaxStars;i++)
    {
    TheStar = &Stars[i];
    if ( (TheStar->X += 4) > MaxXRes )
        {
        TheStar->X = -4;
        TheStar->Y = random(MaxYRes);
        }
    TheLine->x1 = (TheLine->x0 = TheStar->X) + 4;
    TheLine->y1 = TheLine->y0 = TheStar->Y;
    GsSortGLine(TheLine,ActiveOTPtr,StarsPri); 
    }

This way, only setting the X and Y attributes and passing the pointers to
GsSortGLine should be faster in accessing half the main memory than before.
Anyway, I'll take a look at your library sometime soon.

	Germain ( doctor Z ) Sauvé

P.S. Excuse my crappy english.