This page describes how automatic layout can be configured for a given application. This includes how layout options can be set on graph elements, and how they are applied by KIML during the layout process. After having read this, you should be able to answer the following questions:

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Contents

Layout Options and What They Are Good For

Even the most basic layout algorithm provides some settings for you to play with. This might be something as simple as the space left between different nodes, or something as complex as changing how node labels are placed and how that influences the size of each node. Each such setting must be registered with KIML as a layout option, and each algorithm must specify exactly which of these options it supports. Registering a layout option is done through one of KIML's extension points and can look like this:

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This tells KIML that the defined layout algorithm supports the border spacing option. And even more, it overrides the default value declared by the layout option and sets it to 20.

The Layout Options Manager

By now, we have an idea of what layout options do and why they are important in the first place. However, we haven't looked at how layout options end up on KGraph elements yet. This is where the LayoutOptionsManager comes in.

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After a layout manager has finished turning a given diagram into its KGraph representation, the layout options manager is asked to enrich the KGraph elements with layout options. The option values can come from different sources: the user might have set some using the layout view; there might be some defaults for certain kinds of diagrams; or the programmer might have decided to attach some layout options to certain elements for just this one layout run. Whatever the source, the options manager is in charge of collecting all these layout option values and making sure they find their way to the correct KGraph element. To start off with a clean plate, it first makes sure there are no layout options attached to the KGraph elements. It then does two things: collect every eligible source of layout options, and transfer layout options to the correct KGraph elements. Sounds easy enough.

The question remains how the layout options sources work. Each source is represented by a class that implements the ILayoutConfig interface, called a layout configuration. KIML currently provides the following layout configurations, each representing a particular source of layout options:

• DefaultLayoutConfig – Sets fixed default values defined for layout options.
• EclipseLayoutConfig – Users can define default layout options to be set on elements that meet certain criteria via the KIML preference page. This layout configuration takes these options and applies them.
• SemanticLayoutConfig – ??? DOCUMENT THIS
• GmfLayoutConfig / GraphitiLayoutConfig – These configurations apply layout options set by the user in the layout view or stored in the notation model file of a diagram.
• VolatileLayoutConfig – A configuration whose only purpose it is to make sure certain layout options are set on certain diagram elements in a particular layout run.

The options manager collects all available and applicable layout configurations and sorts them by priority (incidentally, the configurations were sorted by increasing priority just now). For every graph element, each configuration is asked to provide layout options, starting with the default layout configuration and working through the priority chain.

A Few Details on Layout Configurations

What we just learned is a bit of a simplification of what happens. The layout options manager not only asks each layout configuration to provide layout options for each graph element. Before we look at the details, let's take a look at the methods each layout configuration provides:

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GETVALUE (for the layout view?)

Implementing a Layout Configuration

deciding what options are applicable depending on the context object; setting the options;

Programmatically Setting Layout Options

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