RE: [Plib-devel] Bug with sign of pitch?

[Dave M. <Dav...@dy...>]

rather than translate into an ssg XYZ - HPR coord structure
why not just set the camera matrix?

i hacked this from LookAt in Mesa-3.2/src-glu/glu.c
but i haven't tested it yet

void ssgLookAt( GLdouble eyex, GLdouble eyey, GLdouble eyez,
                GLdouble centerx, GLdouble centery, GLdouble centerz,
                GLdouble upx, GLdouble upy, GLdouble upz )
{
   sgMat4 m;
   GLdouble x[3], y[3], z[3];
   GLdouble mag;

   /* Make rotation matrix */

   /* Z vector */
   z[0] = eyex - centerx;
   z[1] = eyey - centery;
   z[2] = eyez - centerz;
   mag = sqrt( z[0]*z[0] + z[1]*z[1] + z[2]*z[2] );
   if (mag) {  /* mpichler, 19950515 */
      z[0] /= mag;
      z[1] /= mag;
      z[2] /= mag;
   }

   /* Y vector */
   y[0] = upx;
   y[1] = upy;
   y[2] = upz;

   /* X vector = Y cross Z */
   x[0] =  y[1]*z[2] - y[2]*z[1];
   x[1] = -y[0]*z[2] + y[2]*z[0];
   x[2] =  y[0]*z[1] - y[1]*z[0];

   /* Recompute Y = Z cross X */
   y[0] =  z[1]*x[2] - z[2]*x[1];
   y[1] = -z[0]*x[2] + z[2]*x[0];
   y[2] =  z[0]*x[1] - z[1]*x[0];

   /* mpichler, 19950515 */
   /* cross product gives area of parallelogram, which is < 1.0 for
    * non-perpendicular unit-length vectors; so normalize x, y here
    */

   mag = sqrt( x[0]*x[0] + x[1]*x[1] + x[2]*x[2] );
   if (mag) {
      x[0] /= mag;
      x[1] /= mag;
      x[2] /= mag;
   }

   mag = sqrt( y[0]*y[0] + y[1]*y[1] + y[2]*y[2] );
   if (mag) {
      y[0] /= mag;
      y[1] /= mag;
      y[2] /= mag;
   }

#define M(row,col)  m[row][col]
   M(0,0) = x[0];  M(0,1) = x[1];  M(0,2) = x[2];  M(0,3) = 0.0;
   M(1,0) = y[0];  M(1,1) = y[1];  M(1,2) = y[2];  M(1,3) = 0.0;
   M(2,0) = z[0];  M(2,1) = z[1];  M(2,2) = z[2];  M(2,3) = 0.0;
   M(3,0) = -eyex; M(3,1) = -eyey; M(3,2) = -eyez; M(3,3) = 1.0;
#undef M

   ssgSetCamera( m ) ;
}


> Last I looked I didn't see anything like this, but what I would really
> like is some code that would take a directional vector and an up
> vector and translate this into an ssg XYZ - HPR coord structure.
> 
> What I'd like to use this for is given I know my camera position, and
> the position of something I want centered on the screen, I want to
> look directly at it (with control over the up direction.)  For
> example, a chase plane view in a flight sim.
> 
> It's probably a simple thing to impliment, but I just haven't had a
> chance to sit down and think it through ... and if someone has already
> done the work I'd happily use that. :-)
> 
> Regards,
> 
> Curt.