The Coolest Trick: Frame of Reference
Just after we create the moon, we create the moon’s orbit, which is just an empty 3D object—similar to what we did back in Chapter 3, Project: Making an Avatar. Then we add the orbit to Earth:
| | var moon_orbit = new THREE.Object3D(); |
| | earth.add(moon_orbit); |
Adding the moon_orbit to Earth like that means that it’s centered on Earth. And, no matter where Earth goes, this moon_orbit object stays with Earth.
It probably doesn’t seem like it, but this is a crazily important trick in 3D programming. So important, in fact, that it gets a fancy name: frame of reference. Our moon_orbit is a new frame of reference. To see the power of frame-of-reference thinking, we add the moon to the moon_orbit and move it ...
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