RE: [Algorithms] fast triangle-segment test *with precomputation*

[Robert D. <RD...@ac...>]

> This third test is done because of the possibility of a 
> triangle location which has 
> 
> 1) No vertices inside the box
> 2) No edges which intersect any box face
> 
> In this case I compute 4 ( you are right, I overestimated 
> when I tried to visualise this! :) ) line segments and test if these 
> intersect the face of the triangle.
> 
> Having just looked at your reply you are also right in that 4 
> parallel box edges would do exactly the same thing as 4 diagonal lines.

Actually this is not true ... if the triangle was also parallel to the
chosen four parallel box edges, then it could fall between all of them, not
intersect with any of them, and yet still intersect with the box.

The four diagonal lines on the other hand will cover every possible case,
since it is impossible for a plane to pass through the cube without crossing
at least one diagonal somewhere.

Robert