Path: chuka.playstation.co.uk!news
From: Jim <jim@micronetics.com>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: 3D Sprite TMDs?
Date: Fri, 13 Feb 1998 13:07:01 +0000
Organization: PlayStation Net Yaroze (SCEE)
Lines: 109
Message-ID: <34E44575.16C01D17@micronetics.com>
References: <01bce267$32a34140$0300010a@mario> <34E2C6E8.2BA8BD0F@micronetics.com> <6bum6p$4703@scea>
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Michael,

I gave it a shot last night and all is well.  Many thanks!
It looks like I was missing the world translation.

Cheers!

/Jim

Michael Hough wrote:

> Jim wrote in message <34E2C6E8.2BA8BD0F@micronetics.com>...
> >3d sprites rears its head again.. oh that old chestnut..
> >
> >Has there been a solution to this problem yet?  I was up until the early
> hours
> >again this morning trying to
> >place a sprite in three dimensions.  I have something reasonable working,
> just
> >a couple of glitches here and there.  My major problem is I have a roving
> >camera style view and the sprite has trouble translating in relation to its
> >[camera] position.
> >
> >Here's some pseudo code from what I can remember, am I doing anything
> unusual?
> >
> >VECTOR v;    // coord system
> >VECTOR p;    // resulting location for sprite
> >MATRIX m;
> >long x,y;
> >
> >v.vx = 0;  v.vy = 0;  v.vz = 0;
> >GsInitCoordinate2 ( WORLD, &local);        // init coord system
> >GsGetLS (&local, &m);                                // combine with
> >GsWSMATRIX for camera
> >ApplyMatrix (&m, &v, &p);                        // project coordinates
> >
> >// perspective calcs and display here...
> >
> >Now this code produces the expected result ( or at least I convinced myself
> >the result was expected).
> >But if I translate that point or coordinate system anywhere else, I get
> nada,
> >or something unexpected and a bit bizarre..
> >
> >I've not shown the perspective calcs because they were a hack.
> >essentially.
> >
> >x = -p.vx;
> >y = p.vz;        // not a typo with vz
> >
> >But this does place the sprite where it should be..
> >
> >Does ApplyMatrix add the translation terms as well?  I wrote my own version
> of
> >applymatrix to compare the
> >results and I got the same as ApplyMatrix only if I neglected to do the
> >translation.
> >
> >I also get the same result if I replace the GsGetLs with
> >ApplyMatrix (&GsWSMATRIX, &v, &p);
> >
> >I guess as an alternative to this I would have to try a bill boarding
> >approach, although not really ideal for the application I have in mind, and
> >quite possibly slower.
> >
> >Can anyone please help me out, as I don't think I could handle many more
> >sleepless nights.
> >
> >
> >Many thanks
> >Regards
> >
> >Jim
>
> Here's the code I hacked together--it owes a lot to the SCEE 'flying' demo:
>
>   setVector(&sprV,x,y,z);
>
>   PushMatrix();
>
>   ApplyMatrixLV(&GsWSMATRIX, &sprV, &tmpV);
>   tmpV.vx += GsWSMATRIX.t[0];
>   tmpV.vy += GsWSMATRIX.t[1];
>   tmpV.vz += GsWSMATRIX.t[2];
>   if (tmpV.vz == 0) tmpV.vz=1;  // div by zero
>                                 // 512 is SCR_Z
>   sprV.vx = tmpV.vx * 512 / tmpV.vz;
>   sprV.vy = tmpV.vy * 512 / tmpV.vz;
>   sprV.vz = tmpV.vz >> 2;
>
>   PopMatrix();
>
>   spr.scalex=spr.scaley=512*4096/(sprV.vz);
>
> It seems a lot like yours; you can probably use the Ls matrix rather than
> the WS matrix (depending on in whose coordinate system x, y, and z are, no
> doubt).  You do need to do the translation yourself.  The problem is
> probably in your perspective transform; multiply by the screen distance (512
> in this case) and then divide by the sprite distance.  That same number is
> also scaling.  The Push- and PopMatrix() calls are voodoo left over from the
> 'flying' demo.
>
> Good luck!
>
> mike