Path: chuka.playstation.co.uk!news
From: Steve Hunt <steve@itallnight.u-net.com>
Newsgroups: scee.yaroze.programming.2d_graphics,scee.yaroze.programming.3d_graphics
Subject: 3D coord to 2D screen coord
Date: Sat, 23 May 1998 17:26:32 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Xref: chuka.playstation.co.uk scee.yaroze.programming.2d_graphics:363 scee.yaroze.programming.3d_graphics:582

Hi,

	Someone a bit ago ask how to convert a 3d x,y,z coord into a 2d
	screen x,y coord.

	Well here's some code that does just that....

	Code assumes that the 2d origin is in the center of the screen.

	ProjectionDistance is what ever value you passed to GsSetProjection();

	Call InitTransProj() once to set things up,
	then TransProj to get the screen coord of your 3d object.

	Enjoy,

Steve


CODE........


void InitTransProj(void);
void TransProj(VECTOR *pos, short *x, short *y);

static GsCOORDINATE2 trans;

//
-------------------------------------------------------------------------
//	init trans proj coord
//
-------------------------------------------------------------------------
void InitTransProj()
{
	GsInitCoordinate2(WORLD, &trans);
}

//
-------------------------------------------------------------------------
//	Trans Proj - convert 3d x,y,z to 2d screen x,y
//
-------------------------------------------------------------------------
void TransProj(VECTOR *pos, short *x, short *y)
{
	MATRIX mat;
	VECTOR v;

	trans.coord.t[0] = pos->vx;
	trans.coord.t[1] = pos->vy;
	trans.coord.t[2] = pos->vz;
	trans.flg = 0;

	GsGetLs(&trans, &mat);

	ApplyMatrixLV(&mat, pos, &v);

	if(mat.t[2]) {
		*x = ProjectionDistance * v.vx / mat.t[2];
		*y = ProjectionDistance * v.vy / mat.t[2];
	} else {
		*x = 0;
		*y = 0;
	}
}