Class SpotRotatingTool

GoJS® Diagramming Components
version 3.0.0
by Northwoods Software®

This is an extension and not part of the main GoJS library. Note that the API for this class may change at any time. If you intend to use an extension in production, you should copy the code to your own source directory. See the Extensions intro page for more information.


A custom RotatingTool that also supports the user moving the point about which the object is rotated.

Typical usage:

  new go.Diagram(. . .,
rotatingTool: new SpotRotatingTool(),
. . .

This tool uses two separate Adornments -- the regular one holding the rotation handle and an additional one named "MovingSpot" that holds the handle for interactively moving the go.RotatingTool.rotationPoint by changing the go.Part.rotationSpot.

If you want to experiment with this extension, try the Spot Rotating sample.




  • In addition to the standard behavior of go.RotatingTool.canStart, also start when the user starts dragging the "MovingSpot" adornment/handle.

    Returns boolean


  • Change the positioning of the "Rotating" Adornment to adapt to the rotation point potentially being well outside of the object being rotated.

    This assumes that go.RotatingTool.handleAngle is zero.


    Returns Point

    Point in document coordinates

  • This is called by mouse moves and mouse up events when the handle being dragged is "MovingSpot". This needs to update the go.Part.rotationSpot and go.RotatingTool.rotationPoint properties.

    For each of the X and Y directions, when the handle is within the bounds of the rotated object, the new rotation Spot will be purely fractional; when it is outside the Spot will be limited to a fraction of zero or one (whichever is closer) and an absolute offset that places the rotation point where the handle is.

    Returns void

  • In addition to updating the standard "Rotating" Adornment, this updates a "MovingSpot" Adornment that the user may drag in order to move the go.RotatingTool.rotationPoint.


    Returns void