Animate object along a path in three.js

Question

I am trying to animate a cube along a path in three.js.

CODE

 // Ellipse class, which extends the virtual base class Curve
    var curve = new THREE.EllipseCurve(
        0,  0,            // ax, aY
        16, 21.28,           // xRadius, yRadius
        0,  2 * Math.PI,  // aStartAngle, aEndAngle
        false,            // aClockwise
        0                 // aRotation
    );

    //defines the amount of points the path will have
    var path = new THREE.Path( curve.getPoints( 100 ) );
    var geometrycirc = path.createPointsGeometry( 100 );
    var materialcirc = new THREE.LineBasicMaterial( {
        color : 0xff0000
    } );

    // Create the final object to add to the scene
    var ellipse = new THREE.Line( geometrycirc, materialcirc );
    ellipse.position.set(0,1,0);
    this.scene.add( ellipse );

    // add the box to the scene
    this.scene.add(this.box);

I have being doing some research into how this could be done and came across this fiddle animate on path This method uses a the THREE.SplineCurve3 method to create the points for the box to use.

My question is do I need to convert my path to use the THREE.SplineCurve3 method.

Or can I use the path as it is?

Any help or pointers would be appreciated.

many thanks

Answer 1

Object Animating on path

Code

// GLOBALS - ALLOCATE THESE OUTSIDE OF THE RENDER LOOP - CHANGED
var cubes = [], marker, spline;
var matrix = new THREE.Matrix4();
var up = new THREE.Vector3( 0, 1, 0 );
var axis = new THREE.Vector3( );
var pt, radians, axis, tangent, path;

// the getPoint starting variable - !important - You get me ;)
var t = 0;

//This function generates the cube and chooses a random color for it 
//on initial load.

function getCube(){
// cube mats and cube
var mats = [];
for (var i = 0; i < 6; i ++) {
    mats.push(new 
THREE.MeshBasicMaterial({color:Math.random()*0xffffff}));
}

var cube = new THREE.Mesh(
    new THREE.CubeGeometry(2, 2, 2),
    new THREE.MeshFaceMaterial( mats )
);

return cube
}

// Ellipse class, which extends the virtual base class Curve
function Ellipse( xRadius, yRadius ) {

    THREE.Curve.call( this );

    // add radius as a property
    this.xRadius = xRadius;
    this.yRadius = yRadius;

 }

 Ellipse.prototype = Object.create( THREE.Curve.prototype );
 Ellipse.prototype.constructor = Ellipse;

 // define the getPoint function for the subClass
 Ellipse.prototype.getPoint = function ( t ) {

 var radians = 2 * Math.PI * t;

 return new THREE.Vector3( this.xRadius * Math.cos( radians ),
                          this.yRadius * Math.sin( radians ),
                          0 );

};

//

var mesh, renderer, scene, camera, controls;


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( 45, window.innerWidth / window.innerHeight, 1, 1000 );
camera.position.set( 20, 20, 20 );

// controls
controls = new THREE.OrbitControls( camera, renderer.domElement );
controls.addEventListener( 'change', render ); // use if there is no animation loop
controls.minDistance = 10;
controls.maxDistance = 50;

// light
var light = new THREE.PointLight( 0xffffff, 0.7 );
camera.add( light );
scene.add( camera ); // add to scene only because the camera  has a child

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


////////////////////////////////////////
//      Create the cube               //
////////////////////////////////////////

marker = getCube();
marker.position.set(0,0,0);
scene.add(marker);


////////////////////////////////////////
//      Create an Extruded shape      //
////////////////////////////////////////

// path
path = new Ellipse( 5, 10 );

// params
var pathSegments = 64;
var tubeRadius = 0.5;
var radiusSegments = 16;
var closed = true;

var geometry = new THREE.TubeBufferGeometry( path, pathSegments, tubeRadius, radiusSegments, closed );

// material
var material = new THREE.MeshPhongMaterial( {
    color: 0x0080ff, 
} );

// mesh
mesh = new THREE.Mesh( geometry, material );
scene.add( mesh );

//////////////////////////////////////////////////////////////////////////
//       Create the path which is based on our shape above              //
//////////////////////////////////////////////////////////////////////////

//Please note that this red ellipse was only created has a guide so that I could  be certain that the square is true to the tangent and positioning.

// Ellipse class, which extends the virtual base class Curve
    var curve = new THREE.EllipseCurve(
        0,  0,            // ax, aY
        6, 11,           // xRadius, yRadius
        0,  2 * Math.PI,  // aStartAngle, aEndAngle
        false,            // aClockwise
        0                 // aRotation
    );

    //defines the amount of points the path will have
    var path2 = new THREE.Path( curve.getPoints( 100 ) );
     geometrycirc = path2.createPointsGeometry( 100 );
    var materialcirc = new THREE.LineBasicMaterial( {
        color : 0xff0000
    } );

    // Create the final object to add to the scene
    var ellipse = new THREE.Line( geometrycirc, materialcirc );
    ellipse.position.set(0,0,0);
    scene.add( ellipse );

    }

function animate() {
requestAnimationFrame(animate);

render();
}


function render() {

    // set the marker position
    pt = path.getPoint( t );

    // set the marker position
    marker.position.set( pt.x, pt.y, pt.z );

    // get the tangent to the curve
    tangent = path.getTangent( t ).normalize();

    // calculate the axis to rotate around
    axis.crossVectors( up, tangent ).normalize();

    // calcluate the angle between the up vector and the tangent
    radians = Math.acos( up.dot( tangent ) );

    // set the quaternion
    marker.quaternion.setFromAxisAngle( axis, radians );

    t = (t >= 1) ? 0 : t += 0.002;

    renderer.render( scene, camera );

}

init();
animate();

<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/82/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>

Conclusion

So I was very Fortunate to stumble upon the answer. In my case it was the creation of a subclass to my object which allowed me to use it's data as points so that an object could use it as a guide.

Yes I am aware that you are thinking 'What is this guy talking about' so I have created a fiddle for you to look at and study.

Fiddle: Object Animating on path