Only one that pops into my head is a two-part solution.

Build a solid appearing glass with the initial bullet hole and
travelling fracture lines in actual pieces CSG'd together, BUT,
be prepared to do the following:

	nothing more complex then a sequence of mapped on textures using
however many frames you need of 2d art that illustrate the
texture proceeding to crack.  I would do this by using an index
mapped texture map- not sure the exact term, but one where you
index actual texture numbers to you have maximum control over a
set of procedural textures you will define as your need
requires.  Creating these frames can be approached itself in any
number of ways.  I'll go no further on this.

I will say this again, because it needs to be stated twice:
Build the glass in pre-broken pieces that match you fracture
lines.  Do this before building the fracture-line version
indexed-texture map series, because then you have a potential 2d
map to work from. (Big HINT there.)

When you animate, and when it comes to the time after the
fractures are done growing, blow the pieces apart as you will.

This whole process may require serious further innovation and
changes as you proceed.

No, I'll answer no more on this subject, nor elucidate.  I have
finals approaching.  And besides, there are other bigger, smarter
people around here who can help too.

-peter
-- 
Current obsession: "Ballet pour ma fille."
http://www.applesnake.net

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