Delay's Blog is the blog of David Anson, a Microsoft developer who works with C#, XAML, HTML, and Azure.
I described the idea behind my MouseButtonClicker utility in the introductory post for MouseButtonClicker. As you might expect, I've been using this tool ever since I released it a few weeks ago.
All was well - except that every so often I'd get an automatic click that shouldn't have happened. Not frequently enough to stop me from using MouseButtonClicker, but enough to be annoying. I assumed this was simply "jitter" (see the original post for background) beyond what the jitter-prevention code was already filtering out, but I didn't think so because I'd watched the input events and the 2-unit threshold really seemed like it should be large enough.
So one evening when I had a bit of time, I compiled an instrumented version of MouseButtonClicker, started it up, and went about my work. Sure enough, after a half-hour or so, I got an unexpected click! So I had a look at the debug output and found that the bogus click had occurred after a 1-unit jitter movement. But that was below the 2 unit threshold, so the jitter filter should have suppressed the click. To my dismay, it seemed my code had a bug...
And sure enough, once I knew what to look for, I spotted it right off. :) The jitter filter was working fine for the general case - but there was a special case that wasn't handled properly. Specifically, the jitter threshold is always reset when MouseButtonClicker clicks the mouse - because the mouse has stopped moving is likely to stay at rest for a while. However, if the user moved the mouse and clicked the mouse button manually, MouseButtonClicker would suppress its own click (correct behavior) but was neglecting to reset the jitter filter! This problem wasn't immediately obvious to the user because the observable behavior so far was 100% correct - it was only if the mouse was left alone for about 10 minutes and jittered again that the jitter threshold wouldn't do its job and a bogus click would be made.
So I fixed the bug, compiled version 1.01 of MouseButtonClicker, ran with the new bits for a few days to verify the problem was solved (it was!), and updated the public download:
Click here to download the MouseButtonClicker executables (32- and 64-bit) and the complete Visual Studio 2008 source code.
I'm sorry for any trouble this may have caused - I hope the new bits prove even more helpful than the last! :)