What is the method for scrolling the canvas on a touch device using three.js?

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To scroll the canvas on a touch device using three.js, you can use the touchstart, touchmove, and touchend events to detect when the user touches the screen, moves their finger, and lifts their finger, respectively.

Then, you can calculate the distance and direction of the finger movement, and use that data to translate the camera in the opposite direction. This will give the appearance of the canvas scrolling.

Here's an example code snippet that demonstrates the basic idea:

var start = new THREE.Vector2();
var move = new THREE.Vector2();

function onTouchStart(event) {
  start.set(event.touches[0].screenX, event.touches[0].screenY);
}

function onTouchMove(event) {
  move.set(event.touches[0].screenX, event.touches[0].screenY);
  var diff = move.clone().sub(start);
  camera.position.x -= diff.x * 0.05;
  camera.position.y += diff.y * 0.05;
  start.copy(move);
}

function onTouchEnd(event) {
  // do something when the user lifts their finger
}

canvas.addEventListener('touchstart', onTouchStart);
canvas.addEventListener('touchmove', onTouchMove);
canvas.addEventListener('touchend', onTouchEnd);

In this example, the start and move vectors are used to store the position of the finger at the start of the touch event and during the touch event, respectively.

The onTouchStart function is called when the user touches the screen, and it sets the start vector to the coordinates of the touch.

The onTouchMove function is called when the user moves their finger on the screen. It calculates the distance and direction of the finger movement (diff), and translates the camera in the opposite direction using the camera.position property.

Finally, the onTouchEnd function is called when the user lifts their finger from the screen. This function could be used to perform any necessary cleanup or final calculations.

Note that the 0.05 factor used to scale the movement of the camera is arbitrary and may need to be adjusted depending on the specific application.