Shapes: Measuring Length

This is going to be a lackluster blog entry. It's not going to sparkle or wow anyone... but don't let that fool you: it's very useful.

Actually the reason I'm writing this up as its own entry is that it's a crucial part of three custom Strokes included in this blog:

The BrushStroke.

The BristleStroke.

The CharcoalStroke.

The concept is very simple: given a Shape object, we often need a way to talk about the length of that shape. This includes being able to talk about that shape as fraction (from 0% to 100%) and in pixel lengths (iterate over 5 pixels at a time).

The MeasuredShape is designed to address these needs.

There are a couple of possible pitfalls with this class:

1. In Java, a Shape can have several subpaths. If we want to discuss a shape in terms of fractions: it makes sense to break up each subpath into its own object. So it is hazardous to use the constructors that simply take a Shape argument, because they might throw IllegalArgumentExceptions.

2. Also, especially when talking about fractions, it doesn't make sense to talk about unclosed shapes. So there is are two subtly different methods in the MeasuredShape class: getDistance() and getOriginalDistance(). If the path was closed when the MeasuredShape was created: then these will be equal. If the path was unclosed, then the original distance represent the path that was passed to the constructor, and the current distance represents the length of the closed path.

Here is an applet demonstrating one fun method of this class:

This applet takes a circle and lets you adjust the percent drawn and the offset where the drawing begins. (This is handled in just 1 method in the MeasuredShape class.)

The jar (source code included) is available here.