Archive for September, 2010

Drawing Paths: The Basics

In my previous blog post, I presented a fairly complete extension panel for InDesign. This time, I’d like to step back a bit and talk about the process of developing an extension for three Creative Suite applications: Illustrator, InDesign, and Photoshop. We’ll be doing something pretty basic–drawing the same shape in all three applications. While we’re at it, we’ll create a framework we can use to draw any valid shape­. This framework will simplify and standardize the process of drawing a shape, and will work for almost any extension that needs to draw shapes.

In this example, we’ll create a generic extension that can run in any of the above applications, and we’ll keep our application specific code isolated from the overall workings of the extension.

It’s All in the (Application-Specific) Details

The trickiest part of this extension, in fact, is the application-specific code. Illustrator, InDesign, and Photoshop can all draw paths, but each of the applications has a slightly different way of performing the task. In all three applications, you can draw paths using the Pen tool, and the resulting shapes, from a scripting point of view, are made up of paths, which are, in turn, made up of path points. The names and the details of the scripting objects differ a bit between products. In Illustrator and Photoshop, for example, the basic drawing object is a pathItem; in InDesign, it’s a pageItem.

Next, the applications have different ways of dealing with measurement. We’ll need to use measurement values to specify horizontal and vertical coordinates if we’re going to position new path points in a document. In InDesign and Photoshop, you can change measurement units at any time; Illustrator, by contrast, always uses points when it’s being driven by a script. In this example, we’ll be using points, but, for your own scripts, you’ll need to convert measurement values to points before sending them to Illustrator.

In InDesign and Photoshop, path point coordinates are specified relative to the ruler zero point; in Illustrator, they’re specified relative to the lower-left corner of the artboard. Since the default location of the ruler zero point is the upper-left corner of the document in all three applications, this means that the paths in Illustrator will be upside down relative to the paths in the other programs, but we don’t need to worry about that right now.

Finally, Illustrator and InDesign have a number of “shortcuts” for drawing paths with specifc arrangements of points–rectangles, ellipses, regular polygons, etc. We’ll ignore those features in favor of a “one size fits all” drawing routine.

In this tutorial, I’ll present support routines that provide a consistent approach to drawing paths in these applications. The idea is to create a generic drawing function that you can use to build new creative effects (ornamental borders for certificates, for example) or wire into your new data driven graphics feature.

You can download the project here (note that this isn’t really a “finished” extension, it’s just a container for the drawing routines):

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