Low tech and high tech

Remember I've still not gone near my Vectrex yet, and there's more yet to come before I do! I bet this one will comes as a shock.. I need to test the basic maths behind my game, it with involve reflection and as every schoolboy knows with regards to a reflection "the angle of incidence = the angle of reflection" - but I wasn't sure what this meant with regards to the maths in practice..

A few more scribbles and I had a theory, basically I wanted to know it terms of "absolute angles" (compass bearings) what angle a reflection came off at. My pen and paper scribbling came up with
r=2s-b
(where r is the angle of reflection, s is the reflective surface angle and b is the incident beam angle.) I thought it was right but wanted to test it. It's times like this I yearn for the convenient simplicity of an 8-bit microcomputer with integrated BASIC and simple video display commands, like a BBC Micro, sadly times have moved so I reached for the 2007 equivalent.. C# on the Xbox 360! :)

Actually the 360 this is a mixed blessing, for all the time I save with native floating point and trig support, I lose again turning off all the fancy 3D and the textures etc! Anyway about an hour later I had my test (I know an hour's a long time, but C# and the 360 are all new to me!) I took a photo or two:

The red beam is incident, the pink is reflection and the yellow is the reflective surface. The joystick spins the reflective surface and confirms my math to be correct.. I'm ready for the next step..