code: public void computePixel(int which, double x, double y, Point2D_F64 output) {
  		SurfaceRect r = scene.get(which);
  
  		Point3D_F64 p3 = new Point3D_F64(-x,-y,0);
  		SePointOps_F64.transform(r.rectToCamera, p3, p3);
  
  		// unit sphere
  		p3.scale(1.0/p3.norm());
  
  		sphereToPixel.compute(p3.x,p3.y,p3.z,output);
  	}
docs: Project a point which lies on the 2D planar polygon's surface onto the rendered image