Adding number of cubes in three.js

问题

I am trying to add a number of spheres in the following example. Initially it had only three cubes, but I need to add some 10 spheres that would be equidistant from each other and would be rotating in different speeds.

My Try

var parent, renderer, scene, camera, controls;

init();
animate();

function init()
{
    // renderer
    renderer = new THREE.WebGLRenderer();
    renderer.setSize(window.innerWidth, window.innerHeight);
    document.body.appendChild(renderer.domElement);

    // scene
    scene = new THREE.Scene();

    // camera
    camera = new THREE.PerspectiveCamera(40, window.innerWidth / window.innerHeight, 1, 100);
    camera.position.set(20, 20, 20);

    // controls
    controls = new THREE.OrbitControls(camera);
    controls.minDistance = 10;
    controls.maxDistance = 50;

    // axes
    scene.add(new THREE.AxisHelper(20));

    // geometry
    var geometry = new THREE.SphereGeometry(0.3, 50, 50, 0, Math.PI * 2, 0, Math.PI * 2)
    // material
    var material = new THREE.MeshBasicMaterial({
        color: 0xffffff,
        wireframe: true
    });

    // parent
    parent = new THREE.Object3D();
    scene.add(parent);

    // pivots
    var pivot1 = new THREE.Object3D();
    var pivot2 = new THREE.Object3D();
    var pivot3 = new THREE.Object3D();
    var pivot4 = new THREE.Object3D();
    pivot1.rotation.z = 0;
    pivot2.rotation.z = 2 * Math.PI / 3;
    pivot3.rotation.z = 4 * Math.PI / 3;
    pivot4.rotation.z = 6 * Math.PI / 3;
    parent.add(pivot1);
    parent.add(pivot2);
    parent.add(pivot3);
    parent.add(pivot4);

    // mesh
    var mesh1 = new THREE.Mesh(geometry, material);
    var mesh2 = new THREE.Mesh(geometry, material);
    var mesh3 = new THREE.Mesh(geometry, material);
    var mesh4 = new THREE.Mesh(geometry, material);
    mesh1.position.y = 5;
    mesh2.position.y = 5;
    mesh3.position.y = 5;
    mesh4.position.y = 5;
    pivot1.add(mesh1);
    pivot2.add(mesh2);
    pivot3.add(mesh3);
    pivot4.add(mesh4);

}

function animate()
{
    requestAnimationFrame(animate);

    parent.rotation.z += 0.01;

    controls.update();

    renderer.render(scene, camera);
}

Why am I not able to add more than 3 spheres into the scene? I tried to add the fourth sphere but it did not work. How can speed be accounted for here? That is: can I specify different speeds for some spheres?

回答1:

Missing 4th Sphere

You specify:

pivot1.rotation.z = 0;
pivot2.rotation.z = 2 * Math.PI / 3;
pivot3.rotation.z = 4 * Math.PI / 3;
pivot4.rotation.z = 6 * Math.PI / 3;

6 * Math.PI / 3 = 2 * Math.PI

Note, three.js uses radians, therefore 2 * PI is 0 (a full revolution is the same place as no rotation.

So pivot1 and pivot4 have the same effective rotation and your 2 sphere end up in the same place in space.

Speed

You currently handle speed by mutating the z rotation on every frame.

parent.rotation.z += 0.01;

This obviously works just fine for a demo. You can speed it up by moving more per frame (or getting more frames, ie better machine or other upgrades)

parent.rotation.z += 0.04;

Now it rotates at 4 times the speed!

More Spheres

Once you get past working with counts larger than your number of fingers on a hand, I recommend getting generic with arrays. Instead of listing out pivot1, pivot2, pivot3, . . . pivot0451, generate this with a loop. (Functionally you could use ranges if you prefer).

First, we declare how many spheres to make. Then divide up the circle (2 * Math.PI radians to go around). Then for ever sphere, make a pivot. Then, for every pivot, add a mesh. And you're done.

var numberOfSpheres = 10;
var radiansPerSphere = 2 * Math.PI / numberOfSpheres;
// pivots
var pivots = [];
for (var i = 0; i < numberOfSpheres; i++) {
  var pivot = new THREE.Object3D();
  pivot.rotation.z = i * radiansPerSphere;
  parent.add(pivot);
  pivots.push(pivot);
}

var meshes = pivots.map((pivot) => {
  var mesh = new THREE.Mesh(geometry, material);
  mesh.position.y = 5;
  pivot.add(mesh)
  return mesh;
});

I implemented this at this codepen.io

Happy coding.

来源：https://stackoverflow.com/questions/36947341/adding-number-of-cubes-in-three-js

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three.js