/**
* @see <a href="gluLookAt.html">gluLookAt</a>
*/
public void look_at(double eyex, double eyey, double eyez,
double centerx, double centery, double centerz,
double upx, double upy, double upz)
{
Matrix4d matrix = new Matrix4d();
Vector4d eye = new Vector4d(eyex, eyey, eyez, 1.0);
Vector4d center = new Vector4d(centerx, centery, centerz, 1.0);
Vector4d up = new Vector4d(upx, upy, upz, 1.0);
Vector4d forward = new Vector4d();
Vector4d side = new Vector4d();
//-- make rotation matrix
// forward = center - eye
forward.minus(center, eye).normalize();
// side = (forward x up), then normalized
side.cross(forward, up).normalize();
// up = side x forward
up.cross(side, forward);
/* [side_x up_x -forward_x 0]
* [side_y up_y -forward_y 0]
* [side_z up_z -forward_z 0]
* [ 0 0 0 1]
*/
matrix.set_column(side, up, forward.negate(), Vector4d.ZERO);
matrix.set_row(3, 0.0, 0.0, 0.0, 1.0);
gl.mult_matrixd(matrix.m);
//-- translate eye to origin
gl.translated(-eyex, -eyey, -eyez);
}