在cannon.js中相对于局部旋转定位身体

Question

I have a body in cannon.js that has a quaternion rotation applied to it. I want to move it 100 units along a vector relative to it's local rotation.

Eg

let body = new CANNON.Body({ mass: 0 });
body.quaternion.setFromAxisAngle(new CANNON.Vec3(0,0,1),(2*Math.PI)/6);
body.position.set(0,0,100); //this is wrong

Using body.position.set(x, y, z); moves the body relative to the world rather than the local rotation. I think I need to add a vector after applying the quaternion to it, but the docs for cannon.js aren't particularly helpful so I've not been able to work out how to do it.

Answer 1

Use the Quaternion#vmult method to rotate a vector and Vec3#add to add the result to the position.

let body = new CANNON.Body({ mass: 0 });
body.quaternion.setFromAxisAngle(new CANNON.Vec3(0,0,1),(2*Math.PI)/6);
let relativeVector = new CANNON.Vec3(0,0,100);

// Use quaternion to rotate the relative vector, store result in same vector
body.quaternion.vmult(relativeVector, relativeVector);

// Add position and relative vector, store in body.position
body.position.vadd(relativeVector, body.position);