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Drawlets User's Guide

The best way to understand and use Drawlets is to:

1. Follow the examples (com.rolemodelsoft.drawlet.examples.*)
2. Read Patterns for Drawlets.
3. Read Patterns for Building an Unusually Adaptable Java Framework to understand the philosophy behind the design (note: Drawlets was previously named HotDraw).
4. Study the Design Overview
5. Once you've done these, look through the code.

Design Overview

Although there are over 100 classes in the Drawlets framework, you can get a pretty solid understanding of the entire framework by understanding the fundamental roles played by the various classes, plus a few non-obvious design features.

Fundamental Roles

First we'll explain the basic relationships between the most prominent fundamental roles that the classes in Drawlets may play: You may wish to study Figure 1 as you read the following:

• Anything that can render itself is a Paintable.
• A Drawing is basically a Paintable SequenceOfFigures (or a sequence of Figures). It is expected that one may wish to save their Drawings for future reference.
• Figures draw themselves using one or more properties of a DrawingStyle.
• A DrawingCanvas allows a SequenceOfFigures to be manipulated. (Many implementors of DrawingCanvas let you edit a Drawing... a DrawingCanvas may also have been named an "Easel" as you might prepare to modify a Drawing by putting it on a DrawingCanvas)
• A DrawingCanvas has an active Tool (InputEventHandler) which can be used (among other things) to create or manipulate various kinds of Figures.
• Figures may provide associated Handles (which are InputEventHandlers) that can also draw themselves when called on by a DrawingCanvas.
• When a DrawingCanvas receives an Event, it will pass it on to either a prominent Handle or its active Tool.
• Most Figures and Handles use Locators to know where to draw themselves/

Figure 1: Class Diagram for intended use of Drawlets fundamental roles

Common Roles

In addition to the several Fundamental Roles, there are a few prominent Common Roles:

• Many things can be a FigureHolder.
• Some Locators are associated in some way with Figures; they are FigureHolders. If a Figure has a Locator which is a FigureHolder, it becomes a RelatedLocationListener on the held Figure. (This is what allows Arrows, LineFigures and TextLabels to follow other Figures around, among other things)
• ComponentHolders are anything that holds a Component (i.e. java.awt.Component). Typically implementors of DrawingCanvas will also be ComponentHolders in order to cooperate with various GUI approaches (e.g. AWT or JFC).
• Text is drawn using StringRenderers.
• Text is often retrieved from Figures that are also StringHolders or LabelHolders.

Existing Classes as Roles

• JDK's Rectangle, Polygon, Graphics, and Vector are prominent
• A DrawingCanvas may be a PropertyChangeListener on a Drawing and its Figures. So can anything else for that matter.