[Bf-committers] Boolean tool precision

[Ken Hughes]

Before I head out of town for a few days, thought I'd throw this at the 
list and see what people's thoughts were:

Chris and I have been working on some of the bugs in the boolean tools:

http://projects.blender.org/tracker/?func=detail&atid=125&aid=6847&group_id=9

I've fixed a few problems, but the one I'm running up against now is 
numeric precision.  Tests for "equal to zero" are causing some resulting 
meshes to have holes (i.e., non-manifold).  Scaling up the sizes of the 
objects prior to applying the boolean operations can fix this.

I've experimented with making the "equal to zero" tests scale based on 
the size of the values being compared, using the floating point numbers 
exponent and mantissa (see frexp() in math.h).  This gives much better 
results, but at the cost of speed: as much as 20% slower in some of my 
tests.

I'm open to other suggestions how to handle this, or just live with one 
of these two options:  fast but possibly non-manifold, slower but almost 
always manifold.

Ken