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Rotating Ellipse Curve in Three.js

Goal
I am trying to create an EllipseCurve (https://threejs.org/docs/#api/en/extras/curves/EllipseCurve) on which a camera should move.
What I did to achive the goal?
This is the code for the ellipse so far.
var curve = new THREE.EllipseCurve(
0,0,
1, 1,
0, 2 * Math.PI,
false,
1.57
)
const points = curve.getPoints( 50 );
const geometry = new THREE.BufferGeometry().setFromPoints( points );
var material = new THREE.LineBasicMaterial( { color : 0xffffff } );
// Create the final object to add to the scene
var curveObject = new THREE.Line( geometry, material );
scene.add(curveObject);
I can see it in the scene like this:
The Problem
I tried to rotate the Ellipse Curve 90 degree arround the x axis clockwise. As I understood from the documentation, the last parameter of the defining function should rotate it.
const curve = new THREE.EllipseCurve(
0, 0, // ax, aY
10, 10, // xRadius, yRadius
0, 2 * Math.PI, // aStartAngle, aEndAngle
false, // aClockwise
0 // aRotation
);
Thank you in advance for you answer. I am quite new to Three.js so sorry if this question might be stupid :D

Get a point on the curve and apply a matrix4 to it.
Here is a concept of how you can do it (see the lines with cam in the animation loop, better to watch with "Full page"):
body{
overflow: hidden;
margin: 0;
}
<script type="module">
import * as THREE from "https://cdn.skypack.dev/three#0.134.0";
import {
OrbitControls
} from "https://cdn.skypack.dev/three#0.134.0/examples/jsm/controls/OrbitControls.js";
let scene = new THREE.Scene();
let camera = new THREE.PerspectiveCamera(60, innerWidth / innerHeight, 1, 1000);
camera.position.set(-10, 10, 10);
let renderer = new THREE.WebGLRenderer({
antialias: true
});
renderer.setSize(innerWidth, innerHeight);
renderer.autoClear = false;
document.body.appendChild(renderer.domElement);
window.addEventListener("resize", () => {
camera.aspect = innerWidth / innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(innerWidth, innerHeight);
})
let controls = new OrbitControls(camera, renderer.domElement);
let light = new THREE.DirectionalLight(0xffffff, 1);
light.position.setScalar(1);
scene.add(light, new THREE.AmbientLight(0xffffff, 0.5));
let grid = new THREE.GridHelper();
grid.position.y = -5;
scene.add(grid);
let obj = new THREE.Mesh(new THREE.IcosahedronGeometry(1, 0), new THREE.MeshLambertMaterial({
color: "aqua"
}));
scene.add(obj);
let curve = new THREE.EllipseCurve(0, 0, 10, 5);
let line = new THREE.Line(new THREE.BufferGeometry().setFromPoints(curve.getSpacedPoints(100)), new THREE.LineBasicMaterial({
color: "yellow"
}));
line.rotation.x = -Math.PI * 0.25;
line.rotation.z = Math.PI * 0.125;
line.position.x = 5;
scene.add(line);
let cam = new THREE.PerspectiveCamera(25, 1, 1.5, 25);
let camHelper = new THREE.CameraHelper(cam);
scene.add(camHelper);
let clock = new THREE.Clock();
let v = new THREE.Vector3();
renderer.setAnimationLoop(() => {
let t = (clock.getElapsedTime() * 0.05) % 1;
// magic is in these lines //////////////////
cam.position.copy(curve.getPointAt(t, v));
cam.position.applyMatrix4(line.matrixWorld);
cam.lookAt(obj.position);
/////////////////////////////////////////////
renderer.clear();
renderer.setViewport(0, 0, innerWidth, innerHeight);
renderer.render(scene, camera);
renderer.setViewport(0, innerHeight - 256, 256, 256);
renderer.render(scene, cam);
})
</script>

the aRotation, angle-rotation, will affect the local origin of other angle settings for this curve. It is not the overall ellipse rotation, but the orientation of any offset relative to default. A different starting point. It would turn a Pac-Man mouth into a backwards Pac-Man mouth at +/- 180-degrees. To rotate the overall curve in world-space, use one of the various methods available, such as curve.rotation.set(0,1,0) or rotation.y += 1. Please refer to documentation for specific variants of rotation.

Three.js – Create half a ring and animate it

I've created a Ring and would like to have only half of it. And after that animate it, that it builds itself up from 0 to half.
var geometry = new THREE.RingGeometry(10, 9, 32);
var material = new THREE.MeshBasicMaterial({
color: 0xffff00,
side: THREE.DoubleSide,
});
var mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);
How can I archive it? I'm new to three.js.

Use thetaStart and thetaLength to animate the half-ring.
body{
overflow: hidden;
margin: 0;
}
<script type="module">
import * as THREE from "https://cdn.jsdelivr.net/npm/three#0.118.3/build/three.module.js";
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera(60, innerWidth / innerHeight, 1, 100);
camera.position.set(0, 0, 10);
var renderer = new THREE.WebGLRenderer({antialias: true});
renderer.setSize(innerWidth, innerHeight);
document.body.appendChild(renderer.domElement);
var grid = new THREE.GridHelper(10, 10);
grid.rotation.x = Math.PI * 0.5;
scene.add(grid);
var innerRadius = 1;
var outerRadius = 2;
// re-building geometry
var usualRingGeom = new THREE.RingBufferGeometry(innerRadius, outerRadius, 32, 1, 0, 1);
var usualRingMat = new THREE.MeshBasicMaterial({color: 0xffff00});
var usualRing = new THREE.Mesh(usualRingGeom, usualRingMat);
scene.add(usualRing);
var clock = new THREE.Clock();
renderer.setAnimationLoop(()=>{
let t = clock.getElapsedTime();
// re-building geometry
usualRingGeom = new THREE.RingBufferGeometry(innerRadius, outerRadius, 32, 1, 0, (Math.sin(t) * 0.5 + 0.5) * Math.PI);
usualRing.geometry.dispose();
usualRing.geometry = usualRingGeom;
renderer.render(scene, camera);
});
</script>
PS You also can achieve the same result without re-building a geometry. For that, you can bend a plane in js (changing vertices) or in shaders :)

Creating a cylinder with slanted bottom

I want to create a cylinder with slanted bottom shape in three.js.
I don't see any direct way to create such geometry in three.js. I tried to see if I can cut the cylinder by a slanted plane, but could not find such operation in the documentation. Can anybody suggest a way to create this?

You can operate with vertices as you want.
Just a simple concept:
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera(60, window.innerWidth / window.innerHeight, 1, 1000);
camera.position.set(0, 0, 10);
var renderer = new THREE.WebGLRenderer({
antialias: true
});
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
var controls = new THREE.OrbitControls(camera, renderer.domElement);
var light = new THREE.DirectionalLight(0xffffff, 0.5);
light.position.setScalar(10);
scene.add(light);
scene.add(new THREE.AmbientLight(0xffffff, 0.5));
var cylGeom = new THREE.CylinderBufferGeometry(1, 1, 5, 16);
var vertices = cylGeom.attributes.position;
// change upper vertices
var v3 = new THREE.Vector3(); // temp vector
for (let i = 0; i < vertices.count; i++) {
v3.fromBufferAttribute(vertices, i); // set the temp vector
v3.y = v3.y > 0 ? (v3.x * 0.5) + 2.5 : v3.y; // change position by condition and equation
vertices.setY(i, v3.y); // set Y-component of a vertex
}
var cylMat = new THREE.MeshLambertMaterial({
color: "aqua"
});
var cyl = new THREE.Mesh(cylGeom, cylMat);
scene.add(cyl);
renderer.setAnimationLoop(() => {
renderer.render(scene, camera)
});
body {
overflow: hidden;
margin: 0;
}
<script src="https://threejs.org/build/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>

Set 3d cube rotation origin

I have a simple 3d cube (BoxGeometry of 100, 100, 100) and I am trying to rotate it. If we call all 100x100x100 a tile - when I rotate it I can see it's overlapping the below tile.
(by changing color, now I totally understand the behaviour).
tl.to(this.cube4.rotation, 0.5, {z: -45* Math.PI/180});
[
What if I want to rotate it based on an anchor point of right bottom? So instead of overflowing inside the below tile, it will overflow that portion to above tile.
So it will look like the green example and not the red example:
The red example here is achieved by
tl.to(this.cube4.rotation, 0.5, {z: -45* Math.PI/180});
tl.to(this.cube4.position, 0.5, {x: 50 }, 0.5);
I am very new to three.js so if any terminology is wrong, please warn me

Add the ("red") cube to a THREE.Group, in that way that the rotation axis (the edge) is in the origin of the group. This means the cube has to be shifted by the half side length.
If you rotate the group object, then the cube (which is inside the group) will rotate around the edge and not around its center.
e.g.
var bbox = new THREE.Box3().setFromObject(cube);
cube.position.set(bbox.min.x, bbox.max.y, 0);
var pivot = new THREE.Group();
pivot.add(cube);
scene.add(pivot);
See also the answer to How to center a group of objects?, which uses this solution to rotate a group of objects.
(function onLoad() {
var camera, scene, renderer, orbitControls, pivot;
var rot = 0.02;
init();
animate();
function init() {
container = document.getElementById('container');
renderer = new THREE.WebGLRenderer({
antialias: true,
alpha: true
});
renderer.setPixelRatio(window.devicePixelRatio);
renderer.setSize(window.innerWidth, window.innerHeight);
renderer.shadowMap.enabled = true;
container.appendChild(renderer.domElement);
camera = new THREE.PerspectiveCamera(70, window.innerWidth / window.innerHeight, 1, 100);
camera.position.set(4, 1, 2);
//camera.lookAt( -1, 0, 0 );
loader = new THREE.TextureLoader();
loader.setCrossOrigin("");
scene = new THREE.Scene();
scene.background = new THREE.Color(0xffffff);
scene.add(camera);
window.onresize = function() {
renderer.setSize(window.innerWidth, window.innerHeight);
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
}
orbitControls = new THREE.OrbitControls(camera, container);
var ambientLight = new THREE.AmbientLight(0x404040);
scene.add(ambientLight);
var directionalLight = new THREE.DirectionalLight( 0xffffff, 0.5 );
directionalLight.position.set(1,2,-1.5);
scene.add( directionalLight );
addGridHelper();
createModel();
}
function createModel() {
var material = new THREE.MeshPhongMaterial({color:'#80f080'});
var geometry = new THREE.BoxGeometry( 1, 1, 1 );
var cube1 = new THREE.Mesh(geometry, material);
cube1.position.set(0,-0.5,-0.5);
var cube2 = new THREE.Mesh(geometry, material);
cube2.position.set(0,0.5,-0.5);
var cube3 = new THREE.Mesh(geometry, material);
cube3.position.set(0,-0.5,0.5);
var material2 = new THREE.MeshPhongMaterial({color:'#f08080'});
var cube4 = new THREE.Mesh(geometry, material2);
var bbox = new THREE.Box3().setFromObject(cube4);
cube4.position.set(bbox.min.x, bbox.max.y, 0);
pivot = new THREE.Group();
pivot.add(cube4);
pivot.position.set(-bbox.min.x, 0.5-bbox.max.y, 0.5);
scene.add(cube1);
scene.add(cube2);
scene.add(cube3);
scene.add(pivot);
}
function addGridHelper() {
var helper = new THREE.GridHelper(100, 100);
helper.material.opacity = 0.25;
helper.material.transparent = true;
scene.add(helper);
var axis = new THREE.AxesHelper(1000);
scene.add(axis);
}
function animate() {
requestAnimationFrame(animate);
orbitControls.update();
pivot.rotation.z += rot;
if (pivot.rotation.z > 0.0 || pivot.rotation.z < -Math.PI/2) rot *= -1;
render();
}
function render() {
renderer.render(scene, camera);
}
})();
<!--script src="https://threejs.org/build/three.js"></!--script-->
<script src="https://rawcdn.githack.com/mrdoob/three.js/r124/build/three.js"></script>
<script src="https://rawcdn.githack.com/mrdoob/three.js/r124/examples/js/controls/OrbitControls.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/tween.js/17.2.0/Tween.js"></script>
<div id="container"></div>

From the first image, it appears that the pivot of your red tile is at its center.
For the rotation you want, you would ideally change the pivot to the lower right of the cube. This is impossible without modifying the geometry of the cube.
BUT a simple trick is to create an empty node at that pivot point, parent your cube to that empty, and apply your rotation to the empty. (Don't forget to remove your translation, you don't need it anymore)
Here is some pseudo code, assuming your red box is centered at (0,0,0) and has a width and height of 100:
// create an empty node at desired rotation pivot
var empty = new Object3D or group
empty.position = (50, -50, 0)
// parent your cube to the empty
var cube = your box
empty.add(cube)
// you may need to change the local position of your cube to bring it back to its global position of (0,0,0)
cube.position = (-50, 50, 0)
rotate empty by 45°

I think you can get the bounds of the rotated object like this:
bounds = new THREE.Box3().setFromObject( theRedObject )
Then reposition the object.y based on its bounds.min.y
let scene, camera, controls, ambient, point, loader, renderer, container, stats;
const targetRotation = 0;
const targetRotationOnMouseDown = 0;
const mouseX = 0;
const mouseXOnMouseDown = 0;
const windowHalfX = window.innerWidth / 2;
const windowHalfY = window.innerHeight / 2;
init();
animate();
var box, b1, b2, b3;
function init() {
// Create a scene which will hold all our meshes to be rendered
scene = new THREE.Scene();
// Create and position a camera
camera = new THREE.PerspectiveCamera(
60, // Field of view
window.innerWidth / window.innerHeight, // Aspect ratio
/*window.innerWidth / -8,
window.innerWidth / 8,
window.innerHeight / 8,
window.innerHeight / -8,
*/
0.1, // Near clipping pane
1000 // Far clipping pane
);
scene.add(camera)
// Reposition the camera
camera.position.set(0, 5, 10);
// Point the camera at a given coordinate
camera.lookAt(new THREE.Vector3(0, 0, 0));
// Add orbit control
controls = new THREE.OrbitControls(camera);
controls.target.set(0, -0.5, 0);
controls.update();
// Add an ambient lights
ambient = new THREE.AmbientLight(0xffffff, 0.2);
scene.add(ambient);
// Add a point light that will cast shadows
point = new THREE.PointLight(0xffffff, 1);
point.position.set(25, 50, 25);
point.castShadow = true;
point.shadow.mapSize.width = 1024;
point.shadow.mapSize.height = 1024;
scene.add(point);
group = new THREE.Group();
group.position.y = 0;
scene.add(group);
rotationAnchor = new THREE.Object3D()
group.add(rotationAnchor);
box = new THREE.Mesh(new THREE.BoxGeometry(), new THREE.MeshStandardMaterial({
color: 'grey'
}))
b1 = box.clone();
b2 = box.clone();
b3 = box.clone();
b3.material = b3.material.clone()
b3.material.color.set('red')
group.add(box);
group.add(b1);
b1.position.y += 1
group.add(b2);
b2.position.z += 1
rotationAnchor.add(b3);
rotationAnchor.position.set(0.5, 0.5, 1.5)
b3.position.set(-.5, -.5, -.5)
// Create a renderer
renderer = new THREE.WebGLRenderer({
antialias: true
});
// Set size
renderer.setPixelRatio(window.devicePixelRatio);
renderer.setSize(window.innerWidth, window.innerHeight);
// Set color
renderer.setClearColor(0xf8a5c2);
renderer.gammaOutput = true;
// Enable shadow mapping
renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap;
// Append to the document
container = document.createElement("div");
document.body.appendChild(container);
document.body.appendChild(renderer.domElement);
// Add resize listener
window.addEventListener("resize", onWindowResize, false);
// Enable FPS stats
stats = new Stats();
container.appendChild(stats.dom);
var gui = new dat.GUI({
height: 5 * 32 - 1
});
let params = {
'test': 4,
'bevelThickness': 1,
'bevelSize': 1.5,
'bevelSegments': 3
}
gui.add(params, 'test', 0, 10).onChange(val => {
test = val
})
}
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(window.innerWidth, window.innerHeight);
}
function animate() {
rotationAnchor.rotation.z = (Math.cos(performance.now() * 0.001) * Math.PI * 0.25) + (Math.PI * 1.25)
requestAnimationFrame(animate);
// Re-render scene
renderer.render(scene, camera);
// Update stats
stats.update();
}
body {
overflow: hidden;
margin: 0;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/96/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>
<script src="https://threejs.org/examples/js/libs/stats.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/dat-gui/0.7.2/dat.gui.min.js"></script>

BoxGeometry sides

I already asked a Question here: Add Thickness to faces
The core question is solved but i ran into another problem.
Before my walls were set on side:THREE.BackSide so that they didnt show when they faced the camera but now when they have a thickness that doesnt work anymore and i dont realy understand why.
Before:
Before
After: After
How can i make the thick walls behave like the Plane walls ?

A very rough concept of controlling the visibility of a wall (I've slightly changed translating and positioning of a geometry):
var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera(60, window.innerWidth / window.innerHeight, 1, 1000);
camera.position.set(0, 5, 5);
camera.lookAt(scene.position);
var renderer = new THREE.WebGLRenderer({
antialias: true
});
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
var controls = new THREE.OrbitControls(camera, renderer.domElement);
scene.add(new THREE.GridHelper(10, 10));
var points = [
new THREE.Vector3(-2, 0, 2),
new THREE.Vector3(2, 0, 2),
new THREE.Vector3(2, 0, -2),
new THREE.Vector3(-2, 0, -2)
]
var walls = [];
points.forEach((p, idx, points) => {
let nextIdx = idx === points.length - 1 ? 0 : idx + 1;
buildWall(p, points[nextIdx], 2, 0.1);
});
function buildWall(pointStart, pointEnd, height, thickness) {
var boxW = pointEnd.clone().sub(pointStart).length();
var boxH = height;
var boxD = thickness;
var boxGeometry = new THREE.BoxGeometry(boxW, boxH, boxD);
boxGeometry.translate(0, boxH * 0.5, 0);
boxGeometry.rotateY(-Math.PI * 0.5);
var wall = new THREE.Mesh(boxGeometry, new THREE.MeshBasicMaterial({
color: "aqua",
wireframe: true
}));
wall.position.copy(pointStart).add(pointEnd).multiplyScalar(0.5);
wall.lookAt(pointEnd);
scene.add(wall);
walls.push(wall);
}
var currentPosition = new THREE.Vector3();
render();
function render() {
requestAnimationFrame(render);
walls.forEach(w => {
w.visible = currentPosition.copy(w.position).sub(camera.position).lengthSq() > camera.position.lengthSq();
})
renderer.render(scene, camera);
}
body {
overflow: hidden;
margin: 0;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/91/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>