Path: chuka.playstation.co.uk!news
From: James Russell <James_Russell@scee.sony.co.uk>
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: 2d sprites in a 3d world
Date: Mon, 23 Nov 1998 21:37:53 +0000
Organization: Sony Computer Entertainment Europe
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"Harvey.C" wrote:
> 
> I'm currently writing a 3d racing game (being my first attempt at 3d),
> and I was wondering how you go about treating 2d sprites as 3d objects.
> For example, games like duke nukem 3d or vrally (with its track side
> detail).

To put a sprite in a 3D world, you must have figured out its world coordinates. Once you've got
these, you transform them using the standard 3D transformation equations to get the X and Y screen
coordinates, and the OT priority.

Assuming you've set your World->Screen Matrix up (as you do when you call GsSetRefView2), then you
need to do the following:

H is your projection distance that you set with GsSetProjectionDistance();

extern MATRIX GsMATRIX;

VECTOR spritePosition,transformedPosition;

spritePosition.vx = sprite's X position in world coords
spritePosition.vy = sprite's Y position in world coords
spritePosition.vz = sprite's Z position in world coords

ApplyMatrixLV(&GsMATRIX,&spritePosition, &transformedPosition);

if(transformedPosition.vz >= 0) {	// If less than 0, then it's behind the camera
	sprite.x = transformedPosition.vx * H / transformedPosition.vz;
	sprite.y = transformedPosition.vy * H / transformedPosition.vz;
	priority = transformedPosition.vz >> (14 - OTLENGTH);
		// Where OTLENGTH is from 1 to 14, remember
	GsSortSprite(&sprite,&myOT[GsActiveBuff()], priority);
}


Erm.. That's all off the top of my head though - let me know if it works!

Cheers,

James

-- 
== James_Russell@scee.sony.co.uk                +44 (171) 447-1626
== Developer Support Engineer - Sony Computer Entertainment Europe

C++ programmers do it with private members and public objects.