function MoveTool(context, root) {
    this.lastMove = null;
    this.context = context;
    this.root = root;
    this.transformInfo = o3djs.picking.createTransformInfo(root, null);
    this.movePlane = [0.0, 0.0, 1.0];
    this.downPoint = null;
    this.selectedObject = null;
  }
  
  /*
   * transform_node : The shape's root node that should be moving.
   *                  (the same node as would be found by our picking code)
   */
  MoveTool.prototype.initializeWithShape = function(transform_node) {
    this.transformInfo.update();
    translation = g_math.matrix4.getTranslation(
        transform_node.getUpdatedWorldMatrix());
    this.downPoint = translation;
    this.selectedObject = transform_node;
    this.lastMove = null;
  };
  
  MoveTool.prototype.handleMouseDown = function(e) {
    var worldRay = o3djs.picking.clientPositionToWorldRay(e.x,
                                                          e.y,
                                                          this.context,
                                                          g_client.width,
                                                          g_client.height);
    this.transformInfo.update();
    this.selectedObject = null;
    var pickInfo = this.transformInfo.pick(worldRay);
    if (pickInfo) {
      pickedObject = pickInfo.shapeInfo.parent;
      while (pickedObject.parent != null &&
             pickedObject.parent.transform != this.root) {
        pickedObject = pickedObject.parent;
      }
      this.selectedObject = pickedObject.transform;
    }
    if (this.selectedObject) {
      this.downPoint = pickInfo.worldIntersectionPosition.slice(0, 3);
      this.lastMove = null;
    }
  };
  
  MoveTool.prototype.handleMouseUp = function(e) {
    this.downPoint = null;
  };
  
  MoveTool.prototype.handleMouseMove = function(e) {
    if (this.downPoint == null)
      return;
  
    if (this.selectedObject === null)
      return;
  
    var offset;
  
    if (e.x !== undefined) {
      // A o3d event
      offset = { x: e.x, y: e.y };
    } else {
      // A JS event
      e = e ? e : window.event;
      elem = e.target ? e.target : e.srcElement;
  
      // Check if the cursor is in the O3D area.
      if (elem !== g_o3dElement) {
        return;
      }
      offset = getRelativeCoordinates(e, elem);
    }
  
    var worldRay = o3djs.picking.clientPositionToWorldRay(offset.x,
                                                          offset.y,
                                                          this.context,
                                                          g_client.width,
                                                          g_client.height);
    // Compute the offset from the start point.
    var ray_dir = g_math.sub(worldRay.far, worldRay.near);
    ray_dir = g_math.normalize(ray_dir);
    var ray_dot_plane = g_math.dot(ray_dir, this.movePlane);
    if (Math.abs(ray_dot_plane) < 0.001) {
      return [0.0, 0.0, 0.0];
    }
    var plane_distance =
        g_math.dot(this.downPoint, this.movePlane) -
        g_math.dot(worldRay.near, this.movePlane);
    t = plane_distance / ray_dot_plane;
    move_position = g_math.add(
        g_math.mul(ray_dir, t), worldRay.near);
    var offset = g_math.sub(move_position, this.downPoint);
    translation = offset;
    if (this.lastMove != null) {
      translation = g_math.sub(offset, this.lastMove);
    }
    this.lastMove = offset;
  
    if (this.selectedObject) {
      matrix = this.selectedObject.localMatrix;
      transformation = g_math.matrix4.translation(translation);
      matrix = g_math.mul(matrix, transformation);
      this.selectedObject.localMatrix = matrix;
    }
  };
  
  MoveTool.prototype.handleKeyDown = function(key) {
    return false;
  };
  
  MoveTool.prototype.handleKeyUp = function(key) {
    // TODO: We should really have a selection instead of this
    //             dual-use of the tool's last selected object.
    if (key == DELETE || key == BACKSPACE) {
      if (this.downPoint == null && this.selectedObject != null) {
        this.selectedObject.setParent(null);
        this.selectedObject = null;
        return true;
      }
    }
    return false;
  };