let velocity = new THREE.Vector3(\r
(this.previousPositions[vertexIndex].x - vertex.x) / dt,\r
(this.previousPositions[vertexIndex].y - vertex.y) / dt,\r
let velocity = new THREE.Vector3(\r
(this.previousPositions[vertexIndex].x - vertex.x) / dt,\r
(this.previousPositions[vertexIndex].y - vertex.y) / dt,\r