OK folks, here's a little update. This version has three different shapes available and the settings are retained in an ini file - custom shapes could be implemented, but could also lead to problems with the transparency and view through, so left it for now.
Tried messing about with the scroll wheel idea, but that proved messy for a quick fix - the problem is that you are running an application, which is easy to capture mouse events in, but the mouse itself is in whichever is the next topmost window, so it needs a global mouse hook - will play about with that later.
Any further thoughts / ideas would be appreciated as this is a neat challenge.
Update v2
http://www.fxc.btint...o.uk/mouseshade2.exe