Re: [Plib-users] How to compute screen coordinates

[Steve B. <sjb...@ai...>]

> Corto Maltese wrote:

> I want to compute the screen (pixels) coordinates in the viewport of a world 3d point.
> How to do that ?
> I know that gluProject can do that....

  "Use the Source Luke".

The sources for gluProject are available from either the SGI reference implementation
of OpenGL or Mesa.

The Mesa source is:

static void transform_point( GLdouble out[4], const GLdouble m[16],
                             const GLdouble in[4] )
{
#define M(row,col)  m[col*4+row]
   out[0] = M(0,0) * in[0] + M(0,1) * in[1] + M(0,2) * in[2] + M(0,3) * in[3];
   out[1] = M(1,0) * in[0] + M(1,1) * in[1] + M(1,2) * in[2] + M(1,3) * in[3];
   out[2] = M(2,0) * in[0] + M(2,1) * in[1] + M(2,2) * in[2] + M(2,3) * in[3];
   out[3] = M(3,0) * in[0] + M(3,1) * in[1] + M(3,2) * in[2] + M(3,3) * in[3];
#undef M
}


GLint GLAPIENTRY gluProject(GLdouble objx,GLdouble objy,GLdouble objz,
                          const GLdouble model[16],const GLdouble proj[16],
                          const GLint viewport[4],
                          GLdouble *winx,GLdouble *winy,GLdouble *winz)
{
    /* matrice de transformation */
    GLdouble in[4],out[4];
 
    /* initilise la matrice et le vecteur a transformer */
    in[0]=objx; in[1]=objy; in[2]=objz; in[3]=1.0;
    transform_point(out,model,in);
    transform_point(in,proj,out);
 
    /* d'ou le resultat normalise entre -1 et 1*/
    if (in[3]==0.0)
       return GL_FALSE;
 
    in[0]/=in[3]; in[1]/=in[3]; in[2]/=in[3];
 
    /* en coordonnees ecran */
    *winx = viewport[0]+(1+in[0])*viewport[2]/2;
    *winy = viewport[1]+(1+in[1])*viewport[3]/2;
    /* entre 0 et 1 suivant z */
    *winz = (1+in[2])/2;
    return GL_TRUE;
}
  

[Cool!  Comments in French!]
                                                                              
> For Steve Baker : You've done a pretty great job with Plib. Bravo!

Let's hope you still feel that way after we produce 1.3.2 later today.

----------------------------- Steve Baker -------------------------------
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