When I'm taking a class, or reading a textbook, or reading an article, there's text that explains a topic, and sometimes illustrations that help visualize the material covered in the text. Sometimes there are diagrams that show things that are not in the text, and charts that summarize data sets that are not included in the text. When these materials are put on the web, those illustrations, diagrams, and charts remain as they were in print: they're static.
In class I often would wonder what would happen if something was changed. For example, in the programming languages course we saw a program and what would happen on the stack and heap to store data. What happens to the stack if you change the order in which you declare variables? I now know the answer to the question, but it would have been nice if I could somehow walk up to the board, change the program text, and watch the diagram of the stack update itself to reflect the change. Although in small classrooms you might be able to convince the instructor to do this, it's completely impractical in a large class to answer every student's question this way. I can't change things in textbooks or articles either.
But now we have the web. There's the possibility of interacting with the course material. Why don't we see much of this?
- When teaching a subject, you have a set of points you want to illustrate. With an exploratory tool the student may or may not actually reach all the points you want to teach. When those points come up in an exam, the student might not be able to answer all the important questions.
- It costs much more to develop interactive material than to develop static material. It's not only the cost of development but also in design.
Web pages are still (mostly) written in the style of books and articles. This is understandable. Films were originally in the style of stage plays. It took experimentation to discover the things you can do by changing scenes, camera angles, etc. A century later, filmmakers are still experimenting, and developing new techniques (examples: showing simultaneous scenes, time lapse, bullet time, showing the same scene from different angles at different times). Web authors have experimented with frames, multiple windows, Java applets for computer algorithms, and writing entire web sites in Flash. I think there will be many more decades of experimentation.
For many years now I've been wanting to put interactive illustrations on my site. There are concepts like distance, movement, pathfinding (A*), scripting, grids, AI, and simulation that I'd like to illustrate. For example I used a Java applet to demonstrate a UI for building roads in simultation games. However I wasn't happy with it. It was a separate page, not integrated into an article that explained the concepts. Java was heavyweight and tricky to get working across browsers. Several authors have produced standalone A* exploration applets or applications, but they too weren't integrated into an article. It wasn't until I saw Raigan and Mare's article about collision detection that I saw what I wanted. Their article uses static illustrations to demonstrate concepts without using interactivity, but makes those illustrations interactive to allow the reader to explore on their own. This addresses my concerns about interactive tools not showing the student the important points. They use Flash to implement their illustrations. Flash is so lightweight that at first I didn't realize their illustrations were interactive. There's no “loading” screen and your browser doesn't slow to a crawl. I don't know how the cost of developing them though.
I had mentioned a few months ago that I haven't been working on my transportation game. It's true, I haven't. I've continued learning Flash but I'm working on diagrams for my site instead of a game. So far my experience has been rather positive. Flash has been easier to learn and use than I expected. The raw graphics libraries are nicer than what I had used before (PyGame, OpenGL, SVG, and Java2D); however, the user interface libraries (buttons, scrollbars, etc.) are worse than those in Java Swing. I especially like that the graphics libraries include things that are useful for illustrations: overlays, translucency, and bevel/glow/shadow effects. For example, you can draw an arrow overlay on top of the illustration without redrawing the illustration itself, or add a glow effect to the object you want the reader to pay attention to. Flash's performance is reasonable. The library reference is nice. There's a free command line compiler for people who don't want to use Adobe's fancy IDE. I'm enjoying it.
My first project has been developing a grid library, using the algorithms from my grid article to generate the illustrations on this page and this page. The most surprising thing for me has been that the 300k of images on those pages could likely be replaced by a 10k Flash file. So far my Flash program compiles to 6.5k, but it doesn't have a UI that lets you select various algorithms and heuristics, and it also doesn't allow you to draw your own obstacles on the grid.
I'm going to follow the style in Raigan and Mare's collision detection tutorial: using Flash to replace static illustrations, not to use Flash for the entire site. I'm also keeping the images as fallbacks for people who don't want or use Flash. Since most of the illustrations need to stand alone without user interaction, the fallback technique works well in this context. While working on the A* illustrations, I realized that my A* pages are nearly ten years old, and my thoughts on the subject have changed somewhat. I'd like to go back and update them to reflect my new thinking. But first, I'm going to add interactive illustrations.
Update:  - I wrote this post in 2007, when Flash was my best choice for interactive diagrams I could embed into a web page. Browsers have advanced quite a bit since then and I'm using HTML5 (SVG and Canvas) for most of my new interactive diagrams.