This is how I do it:
http://www.google.com/search?hl=en&c2coff=1&safe=off&q=Sutherland+Hodgman&spell=1
Basically, you clip the triangle to the box, frustum, whatever, using that algorithm.
If any of the triangle is left at the end, then its inside or intersecting the region.
There is also a way to avoid doing this test entirely by determining ahead of time if all the vertices of triangle are on the outside side of any one of the planes.
You can do that by creating an array which stores which side of each plane each vertex is on in the bits of an integer. Then you can use AND and an OR comparisons to check each vertex in the triangle against these planes all at once.
http://www.google.com/search?hl=en&c2coff=1&safe=off&q=Sutherland+Hodgman&spell=1
Basically, you clip the triangle to the box, frustum, whatever, using that algorithm.
If any of the triangle is left at the end, then its inside or intersecting the region.
There is also a way to avoid doing this test entirely by determining ahead of time if all the vertices of triangle are on the outside side of any one of the planes.
You can do that by creating an array which stores which side of each plane each vertex is on in the bits of an integer. Then you can use AND and an OR comparisons to check each vertex in the triangle against these planes all at once.