touch controls: repeat action until touchend - three.js

Question

I am trying to add touch controls to a three.js scene. I want to move the camera in whatever direction the user touches. It works great using the keyboard because you can press and hold the button and the camera moves continuously. But when I try the same thing using touchstart, you have to keep tapping the screen over and over to move, you can't just hold your finger down like on a keyboard or mouse.
I looked at touchmove, but if you just tap and hold without moving, there are no new touches.
Is there something similar to holding down the keyboard or mousekey using touch events?

Answer 1

There is no builtin callback for a touch event which fires repeatedly like the keyboard. You can, however, simply track the start and end of the touch and then call the move method at a set interval.
First, subscribe to the correct events and set a bool to track the state:
var isTouching = false;
window.addEventListener("touchstart", () => isTouching = true);
window.addEventListener("touchend", () => isTouching = false);
In Three.js you will most likely already have a render loop (e.g. a function called "animate"). Check the state variable at every iteration and apply the movement each time. You may need to also factor in deltaTime (the duration of the last frame), to make movement framerate independent.
function animate() {
requestAnimationFrame(animate);
mesh.rotation.x += 0.005;
mesh.rotation.y += 0.01;
if (isTouching) {
console.log("move camera");
}
renderer.render(scene, camera);
}
Here is a snippet which shows the basic approach. Click and hold in the left or right half of the output window to move the camera.
var camera, scene, renderer, mesh, material, clock;
init();
animate();
var isTouching = false;
var mousePositionX;
window.addEventListener("mousedown", (e) => {
isTouching = true;
mousePositionX = e.clientX;
});
window.addEventListener("mouseup", (e) => isTouching = false);
function init() {
renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
clock = new THREE.Clock();
camera = new THREE.PerspectiveCamera(70, window.innerWidth / window.innerHeight, 1, 1000);
camera.position.z = 400;
scene = new THREE.Scene();
material = new THREE.MeshPhongMaterial();
var geometry = new THREE.BoxGeometry(200, 200, 200);
mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);
var light = new THREE.AmbientLight(0x404040);
scene.add(light);
var directionalLight = new THREE.DirectionalLight(0xffffff);
directionalLight.position.set(1, 1, 1).normalize();
scene.add(directionalLight);
window.addEventListener('resize', onWindowResize, false);
}
function animate() {
requestAnimationFrame(animate);
mesh.rotation.x += 0.005;
mesh.rotation.y += 0.01;
let deltaTime = clock.getDelta();
if (isTouching) {
let speed = 200; // px per second
let movement = speed * deltaTime;
if (mousePositionX > window.innerWidth / 2) {
camera.translateX(-movement);
} else {
camera.translateX(movement);
}
}
renderer.render(scene, camera);
}
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(window.innerWidth, window.innerHeight);
}
body {
padding: 0;
margin: 0;
}
canvas {
display: block;
}
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