Compatible Images

A couple of weeks ago I was tasked with improving the performance on a legacy java swing application that was really crawling.  It would repaint the whole screen on any event, which it could receive a lot of, and painting the whole screen was really slow.  By using compatible images instead of the default kind of image read by ImageIO, the painting code was sped up by a factor of 70 and the event frequency was a non-issue.  The whole change was about 10 lines of code, much less than that to make the software use the graphics clip.

If you are having an issue with graphics performance make sure you try compatible images before trying anything else since it is so easy to introduce.

Before deploying to site I was worried that the speed up I was seeing was in some way down to my dev machine working well with compatible images so I wrote the tool below to test if the improvement was the same which it was.  Some notes:

1. The tool requires an image.  When I attempted to create an in-memory image there was no difference in run times.
2. Results are printed on the command line so remember to use java.exe and not javaw.exe
3. I went to some effort so that this program was a single class to make it easy for the support guys to run.  I don't usually like to implement Runnable on a class that isn't just a Runnable.