This sample demonstrates the LinkShiftingTool, which is an extra tool that can be installed in the ToolManager to allow users to shift the end point of the link to be anywhere along the sides of the port with which it remains connected. This extension tool is defined in its own file, as LinkShiftingTool.js.

This only looks good for ports that occupy the whole of a rectangular node. If you want to restrict the user's permitted sides, you can adapt the `LinkShiftingTool.doReshape` method to do what you want.

### GoJS Features in this sample

#### Links

The Link class is used to implement a visual relationship between nodes. Links are normally created by the presence of link data objects in the GraphLinksModel.linkDataArray or by a parent key reference as the value of the TreeModel.nodeParentKeyProperty of a node data object in a TreeModel. More information can be found in the GoJS Intro.

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#### Tools

Tools handle all input events, such as mouse and keyboard interactions, in a Diagram. There are many kinds of predefined Tool classes that implement all of the common operations that users do.

For flexibility and simplicity, all input events are canonicalized as InputEvents and redirected by the diagram to go to the Diagram.currentTool. By default the Diagram.currentTool is an instance of ToolManager held as the Diagram.toolManager. The ToolManager implements support for all mode-less tools. The ToolManager is responsible for finding another tool that is ready to run and then making it the new current tool. This causes the new tool to process all of the input events (mouse, keyboard, and touch) until the tool decides that it is finished, at which time the diagram's current tool reverts back to the Diagram.defaultTool, which is normally the ToolManager, again.

More information can be found in the GoJS Intro.

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#### GoJS Extensions

GoJS can be extended in a variety of ways. The most common way to change the standard behavior is to set properties on the GraphObject, Diagram, CommandHandler, Tool, or Layout. But when the desired property does not exist, you might need to override methods of CommandHandler, Tool, Layout, Link, or Node. Methods that you can override are documented in the API reference. Various features of GoJS can be overriden, either by replacing a method on an instance (a feature of JavaScript) or by defining a subclass. You should not modify the prototypes of any of the GoJS classes.

In addition to our samples, GoJS provides an extensions gallery, showcasing the creation of custom tools and layouts. Those classes and samples are written in TypeScript, available at `../extensionsJSM/`, as ECMAScript/JavaScript modules -- these use the `../release/go-module.js` library. We recommend that you copy the files that you need into your project, so that you can adjust how they refer to the GoJS library that you choose and so that you can include them into your own building and packaging procedures.

More information can be found in the GoJS Intro.

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#### Geometry Path Strings

The GoJS Geometry class controls the "shape" of a Shape, whereas the Shape.fill and Shape.stroke and other shape properties control the colors and appearance of the shape. For common shape figures, there are predefined geometries that can be used by setting Shape.figure. However one can also define custom geometries.

One can construct any Geometry by allocating and initializing a Geometry of at least one PathFigure holding some PathSegments. But you may find that using the string representation of a Geometry is easier to write and save in a database. Use the static method Geometry.parse or the Shape.geometryString property to transform a geometry path string into a Geometry object.

More information can be found in the GoJS Intro.

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