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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. Extensions can be found in the GoJS kit under the extensions or extensionsTS folders. See the Extensions intro page for more information.


The DragZoomingTool lets the user zoom into a diagram by stretching a box to indicate the new contents of the diagram's viewport (the area of the model shown by the Diagram). Hold down the Shift key in order to zoom out.

The default drag selection box is a magenta rectangle. You can modify the box to customize its appearance.

The diagram that is zoomed by this tool is specified by the zoomedDiagram property. If the value is null, the tool zooms its own Tool.diagram.

You can use this tool in a modal manner by executing:

  diagram.currentTool = new DragZoomingTool();

Use this tool in a mode-less manner by executing:

  myDiagram.toolManager.mouseMoveTools.insertAt(2, new DragZoomingTool());

However when used mode-lessly as a mouse-move tool, in ToolManager.mouseMoveTools, this cannot start running unless there has been a motionless delay after the mouse-down event of at least delay milliseconds.

This tool does not utilize any Adornments or tool handles, but it does temporarily add the box part to the diagram. This tool does not modify the model or conduct any transaction.

If you want to experiment with this extension, try the Drag Zooming sample.




  • Constructs a DragZoomingTool, sets box to a magenta rectangle, and sets name of the tool.

    Returns DragZoomingTool


box : Part

  • Gets or sets the Part used as the "rubber-band zoom box" that is stretched to follow the mouse, as feedback for what area will be passed to zoomToRect upon a mouse-up.

    Initially this is a Part containing only a simple magenta rectangular Shape. The object to be resized should be named "SHAPE". Setting this property does not raise any events.

    Modifying this property while this tool Tool.isActive might have no effect.

delay : number

  • Gets or sets the time in milliseconds for which the mouse must be stationary before this tool can be started.

    The default value is 175 milliseconds. Setting this property does not raise any events.

zoomedDiagram : Diagram | null


Override canStart

  • canStart(): boolean
  • This tool can run when there has been a mouse-drag, far enough away not to be a click, and there has been delay of at least delay milliseconds after the mouse-down before a mouse-move.

    Returns boolean


  • computeBoxBounds(): Rect
  • This just returns a Rect stretching from the mouse-down point to the current mouse point while maintaining the aspect ratio of the zoomedDiagram.

    Returns Rect

    a Rect in document coordinates.

Override doActivate

  • doActivate(): void
  • Capture the mouse and show the box.

    Returns void

Override doDeactivate

  • doDeactivate(): void
  • Release the mouse and remove any box.

    Returns void

Override doMouseMove

  • doMouseMove(): void

Override doMouseUp

  • doMouseUp(): void


  • zoomToRect(r: Rect): void
  • This method is called to change the zoomedDiagram's viewport to match the given rectangle.


    • r: Rect

      a rectangular bounds in document coordinates.

    Returns void

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