docs: function onMouseDown(event) {
      if (scope.enabled === false) return;
  
      if (event.button === 0) {
        state = STATE.ROTATE;
      } else if (event.button === 1) {
        state = STATE.ZOOM;
      } else if (event.button === 2) {
        state = STATE.PAN;
      }
  
      pointerOld.set(event.clientX, event.clientY);
  
      domElement.addEventListener('mousemove', onMouseMove, false);
      domElement.addEventListener('mouseup', onMouseUp, false);
      domElement.addEventListener('mouseout', onMouseUp, false);
      domElement.addEventListener('dblclick', onMouseUp, false);
    }