Simple lookat constraint example for Splice/Maya - used to illustrate rather than edjumakate

splice_lookat_constraint.kl

/*
Classic gl LookAt
 aims down the z axis at the lookAt object
*/
 
// create up and lookAt locators
// create a cube at the origin
// add a spliceMayaNode
// add inputs:
//   lookAt Mat44
//   upVec Mat44
// add Output:
//    result Mat44
// add Opererator:
//    LookAtClassicOp
 
// kl for op

require Math;
 
operator LookAtClassicOp(
  in Mat44 lookAt, // locator
  io Mat44 result,
  in Mat44 upVec // locator
) {
 
 
  // working in world coords, assuming the cube
  // is at origin
  Vec3 z;
  z = lookAt.translation();   // p2 - p1 (lookAt - Vec3(0))  
  z.normalize();
 
  Vec3 x;
  x = upVec.translation().cross(z);
  x.normalize();
 
  Vec3 y;
  y =  z.cross(x);
 
  // splice is column-major
  Mat33 rot(x.x, y.x , z.x,
            x.y, y.y, z.y,
            x.z, y.z, z.z);
           
  Vec3 trans(0.0,0.0,0.0);
  Vec3 scale(1.0,1.0,1.0);
 
 
  result.set(trans, rot, scale);
}

// pipe the result of this node into a decomposeMatrix->Rotate[cube]