"The more simple any thing is, the less liable it is to be
disordered."
Thomas Paine 1776 (from Common Sense)
"Complexity does not necessarily imply disorder." - Philip
Ball
Read Eric
Plante's Tutorial on the rotating-caliper method for intersecting
two
convex polygons. His page also has a beautiful interactive Java applet
you can play with. You can find details and proofs of correctnes of the
algorithm in the PostScript file below.
Godfried T. Toussaint, "A simple linear algorithm for
intersecting
convex polygons," The Visual Computer, vol. 1, 1985, pp.
118-123.