Hi there,
I am looking for a way to animate curved arrows going from point A to B. They can be static as well. But I am not sure where I should start.
Also before I do animation I am also not sure how I can create a curved object that looks like an arrow.
If anyone can point me to right direction, I would really appreciate it.
Thank you.
If you’re using THREE.Curve. (Which I never but this is what I see from the doc)
A simple idea is to use curve.getPoint( t ) while t value is 0-1 (start to end of the curve)
You just need to animate the t value from 0 to 1 from time to time.
And use t value to update your arrow position
arrow.position = curve.getPoint(t);
// Same as above but avoid creating new Vector3 instance.
curve.getPoint(t, arrow.position);
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Perhaps these examples will give you a starting point.
From the Collection of examples from discourse.threejs.org
discourse.threejs.hofk.de getPoint( ) getPointAt( )
2021 eXtended eXamples CurveGenerator
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Thanks for the suggestion by the question. I am close to finishing a multiform geometry (Open source ).
A test resulted in the following
Not yet perfect!
function curvedArrowCenterline( h ) {
return { x: 0.1 * Math.sin( pi * h ), z: 0 };
}
function arrowOutline( h ) {
return{ y: h < 0.9 ? h : ( h === 0.9 ? 0.8 : h ), r: h < 0.9 ? 0.1 : ( h === 0.9 ? 0.2 : 0 ) }
}
UPDATE
Multiform geometry is easier than my Addon. Produces almost infinite many time-varying geometries with functions
It is not a real space curve, but only a horizontal offset of the layers. So a shear per height segment.
In the addon, it is a correctly bent cylinder. However, the arrowhead is not centered due to the height offset. You can create the arrowhead separately and form a group.
The best solution is certainly a specially created geometry.
Here is an example of bending a generic mesh around a curve
I have it there MotionAlongCurve used.
( From the Collection of examples from discourse.threejs.org )
But it does not bend a single mesh. 
See the following posts.
Looks like the box needs segmentation greater, than 1, along X-axis.
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Yeah, needs more vertices in the axes its being curved in.
In fact
I had no subdivision for the example of the movement.
Then an arrow that is curved can be created easily.
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If you need many arrows there is also an instanced version which is useful for animating 100s of objects at the same time such as: XR Koi Garden
2 Likes
Everybody likes Koi fish 
Spline + DataTexture
I looked to see if you can make a curved arrow from the official example
three.js examples LineGeometry
Should work.
<!DOCTYPE html>
<!-- https://discourse.threejs.org/t/how-to-animate-curved-arrows-in-threejs/36808/10 -->
<head>
<title> WebglLinesFat </title>
<meta charset="utf-8">
</head>
<body>
<script type="module">
import * as THREE from '../jsm/three.module.139.js';
import Stats from '../jsm/stats.module.139.js';
import { OrbitControls } from '../jsm/OrbitControls.139.js';
import { LineMaterial } from '../jsm/LineMaterial.139.js';
import { LineSegments2 } from '../jsm/LineSegments2.139.js';
import { Line2 } from '../jsm/Line2.139.js';
import { LineGeometry } from '../jsm/LineGeometry.139.js';
let line, segments ;
let renderer, scene, camera,controls;
let matLine ;
let stats ;
init();
animate();
function init() {
renderer = new THREE.WebGLRenderer( { antialias: true, alpha: true } );
renderer.setPixelRatio( window.devicePixelRatio );
//renderer.setClearColor( 0x000000, 0.0 );
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );
scene = new THREE.Scene();
camera = new THREE.PerspectiveCamera( 65, window.innerWidth / window.innerHeight, 0.001, 1000 );
camera.position.set( 0, 5, 25 );
controls = new OrbitControls( camera, renderer.domElement );
// Position and THREE.Color Data
const positions = [];
//const colors = [];
const points = [];
for ( let i = - 20; i < 20; i ++ ) {
const t = i / 3;
//points.push( new THREE.Vector3( t * Math.sin( 2 * t ), t, t * Math.cos( 2 * t ) ) );
points.push( new THREE.Vector3( t * Math.sin( t / 6 ), t, -t ) );
}
const spline = new THREE.CatmullRomCurve3( points );
const divisions = Math.round( points.length ); //const divisions = Math.round( 3 * points.length );
const point = new THREE.Vector3();
//const color = new THREE.Color();
for ( let i = 0, l = divisions; i < l; i ++ ) {
const t = i / l;
spline.getPoint( t, point );
positions.push( point.x, point.y, point.z );
//color.setHSL( t, 1.0, 0.5 );
//colors.push( color.r, color.g, color.b );
}
const lineGeometry = new LineGeometry();
lineGeometry.setPositions( positions );
//lineGeometry.setColors( colors );
matLine = new LineMaterial( {
color: 0x0000ff, // 0xffffff,
linewidth: 0.75, // in world units with size attenuation, pixels otherwise
worldUnits: true,
//vertexColors: true,
//resolution: // to be set by renderer, eventually
//alphaToCoverage: true,
} );
line = new Line2( lineGeometry, matLine );
// line.computeLineDistances();
// line.scale.set( 1, 1, 1 );
line.scale.set( 1.2, 1.2, 1.2 );
scene.add( line );
//const geo = new THREE.BufferGeometry();
//geo.setAttribute( 'position', new THREE.Float32BufferAttribute( positions, 3 ) );
//geo.setAttribute( 'color', new THREE.Float32BufferAttribute( colors, 3 ) );
window.addEventListener( 'resize', onWindowResize );
onWindowResize();
stats = new Stats();
document.body.appendChild( stats.dom );
}
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize( window.innerWidth, window.innerHeight );
}
function animate() {
requestAnimationFrame( animate );
stats.update();
// main scene
//renderer.setClearColor( 0x000000, 0 );
//renderer.setViewport( 0, 0, window.innerWidth, window.innerHeight );
// renderer will set this eventually
//matLine.resolution.set( window.innerWidth, window.innerHeight ); // resolution of the viewport
renderer.render( scene, camera );
}
</script>
</body>
</html>
1 Like
And here is the arrow.
But you have to create the peak separately, otherwise it is only correct from a distance.
for ( let i = - 25; i <= 0.4; i ++ ) {
points.push( new THREE.Vector3( i / 4 * Math.sin( i / 20 ), 0, -i / 2 ) );
}
for ( let i = - 5; i <= 5; i ++ ) {
points.push( new THREE.Vector3( i / 5 , 0, Math.abs( i / 5 ) ) );
}
const matLine = new LineMaterial( {
color: 0xff00ff,
linewidth: 0.01,
} );
UPDATE:
I just noticed that the visible arrow thickness remains constant as the camera moves further away. I must have removed something from the template that is obviously important. 
1 Like
Try to uncomment this line.
Then the complete line disappears. I’ll probably have to simplify the original example again piece by piece to find the spot.
UPDATE:
I obviously got confused with my various test versions. In one it works. Must bring order into it.
I didn’t get, why does it have to be fat lines?
Is usual THREE.Line() not an option?
… me neither.
Looked at how to do it with a simple line.
With it you can build a beautiful net.
You can make the balls as transparent bubbles and position things in them.
Here only as a wireframe.
The arrow hits the balls on the straight line connecting the centers.
<!DOCTYPE html>
<!-- https://discourse.threejs.org/t/how-to-animate-curved-arrows-in-threejs/36808/17 -->
<head>
<meta charset="utf-8">
<title> CurvedArrowWithTip </title>
<style>
body {
margin: 0;
overflow: hidden;
}
</style>
</head>
<body></body>
<script src='../js/three.139.js'></script>
<script src='../js/OrbitControls.139.js'></script>
<script>
// @author hofk
const scene = new THREE.Scene( );
const renderer = new THREE.WebGLRenderer( { antialias: true } );
renderer.setPixelRatio( window.devicePixelRatio );
renderer.setClearColor( 0xdedede, 1.0 );
renderer.setSize( window.innerWidth, window.innerHeight );
document.body.appendChild( renderer.domElement );
const camera = new THREE.PerspectiveCamera( 65, window.innerWidth / window.innerHeight, 0.1, 1000 );
camera.position.set( -1, 3, 4 );
const controls = new THREE.OrbitControls( camera, renderer.domElement );
window.addEventListener( "resize", event => { camera.aspect = innerWidth / innerHeight; camera.updateProjectionMatrix( );
renderer.setSize(innerWidth, innerHeight ); } );
const gridHelper = new THREE.GridHelper( 5, 10 );
scene.add( gridHelper );
// input data .................................
const v0 = new THREE.Vector3( -1.9, 0.2, 0.4 );
const r0 = 0.16;
const v1 = new THREE.Vector3( 1.7, 0.5, 0.1 );
const r1 = 0.35;
const bend = 0.8; // 0 .. +-1 .. +-2 ...
const φ = -0.9; // radiant, test with 0
//.............................................
const mesh0 = new THREE.Mesh( new THREE.SphereGeometry( r0 ), new THREE.MeshBasicMaterial( { color: 0x11ab22 , wireframe: true } ) );
mesh0.position.set( v0.x, v0.y, v0.z ) ;
scene.add( mesh0 );
const mesh1 = new THREE.Mesh( new THREE.SphereGeometry( r1 ), new THREE.MeshBasicMaterial( { color: 0x11ab22 , wireframe: true } ) );
mesh1.position.set( v1.x, v1.y, v1.z ) ;
scene.add( mesh1 );
const cpc = 100; // bended: curve points count
let points = []; // curve points
const points3 = [];
let k, b, n, r;
const v = new THREE.Vector3( ).subVectors( v1, v0 );
const vn = v.clone( ).normalize( );
const vlen = v.length( );
v0.add( v.normalize( ).multiplyScalar( r0 ) );
v1.sub( v.normalize( ).multiplyScalar( r1 ) );
const vv = new THREE.Vector3( ).subVectors( v1, v0 ).divideScalar( 2 );
// orthogonal see http://lolengine.net/blog/2013/09/21/picking-orthogonal-vector-combing-coconuts
k = ( Math.abs( vn.x ) + 0. ) % 1; // fract
b = new THREE.Vector3( -vn.y, vn.x - k * vn.z, k * vn.y ).normalize( ); // binormal
if( φ !== 0 ) {
const n = new THREE.Vector3( ).crossVectors( vn, b ); // normal
r = new THREE.Vector3( ).addVectors( b.multiplyScalar( Math.cos( φ ) ), n.multiplyScalar( Math.sin( φ ) ) ); // rotated
}
const vm = new THREE.Vector3( ).add( v0 ).add( vv ).add( ( φ === 0 ? b : r ).multiplyScalar( vlen / 4 ).multiplyScalar( bend ) );
points3.push( v0, vm, v1 );
points = new THREE.CatmullRomCurve3( points3 ).getPoints( cpc );
const line = new THREE.Line( new THREE.BufferGeometry( ).setFromPoints( points ), new THREE.LineBasicMaterial( { color: 0xff1122 } ) );
const tipHeight = 0.2;
const tipGeometry = new THREE.ConeGeometry( tipHeight / 4, tipHeight );
tipGeometry.translate( 0, -tipHeight / 2, 0 );
const tipMesh = new THREE.Mesh( tipGeometry , new THREE.MeshBasicMaterial( { color: 0xff1122 , wireframe: true } ) );
const vt = new THREE.Vector3( ).subVectors( points[ cpc ], points[ cpc - Math.floor( 0.05 * cpc ) ] ).normalize( );
tipMesh.quaternion.setFromUnitVectors( new THREE.Vector3( 0, 1, 0 ), vt );
tipMesh.position.set( v1.x, v1.y, v1.z );
line.add( tipMesh ); // scene.add( tipMesh );
scene.add( line );
animate();
function animate() {
requestAnimationFrame( animate );
renderer.render( scene, camera );
}
</script>
</html>
1 Like