I came down with a cold late last night so I have been sitting at the computer for 8 hours today working on frustrum-related programming. Some of the time was spent on our modelling tool called Makeship. Some of the time was used to develop a spreadsheet which can be used to find an inner polygon given a three-dimensional polygon. But most of the time was trying to figure out how to take the 8 vertices that I have yet to calculate and build a projection matrix.
Presumably it can be done since the matrix can store the information we need – but the math is apparently very complicated so we will have to accomplish it through multiple concatenations.
Another approach was to take the 6 planes that are described by the 8 vertices but that was shot down too. I took an excerpt from this article:
… there’s a reason the Digital/VFX industry hasn’t done this already =)