Tldraw/packages/tldraw/src/state/tools/about-tools.md

Tools

Tools are classes that handle events. A tldrawApp instance has a set of tools (tools) and one current tool (currentTool). The state delegates events (such as onPointerMove) to its current tool for handling.

In this way, tools function as a finite state machine: events are always handled by a tool and will only ever be handled by one tool.

BaseTool

Each tool extends BaseTool, which comes with several default methods used by the majority of other tools. If a tool overrides one of the BaseTool methods, consider re-implementing the functionality found in BaseTool. For example, see how StickyTool overrides onPointerUp so that, in addition to completing the current session, the it also sets the state's editingId to the new sticky shape.

Enter and Exit Methods

When the state changes from one tool to another, it will:

1. run the previous tool's onExit method
2. switch to the new tool
3. run the new current tool's onEnter method

Each tool has a status (status) that may be set with setStatus.