The user can resize and rotate the Shape named "SHAPE" in the Nodes. In addition to the normal features of the RotatingTool, the SpotRotatingTool shows a handle at the Part.rotationSpot, which is also at the RotatingTool.rotationPoint. The user can drag that handle and thereby move the rotationPoint and the Part.rotationSpot. When the handle is inside the rectangular area of the Part.rotateObject, the Spot is purely fractional. When the handle moves outside of the object's rectangular area, the spot will be at the edge of the rectangle plus an offset.
This extension tool is defined in its own file, as SpotRotatingTool.js.
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.
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.