This makes the exact boolean have zero weights for any vertex groups
on any newly created vertices, which is what the fast solver does.
The exact boolean solver was interpolating vertex data when interpolating
loop data in newly created faces. Not sure why I chose that. The Fast
boolean solver doesn't do that, so I stopped doing it too.
The existing hash function didn't work well with Set's method of
masking to the lower bits, because many verts have zeros in the
lower bits.
Also, replaced VectorSet with Set for Vert deduping.
The code was trying to ignore hidden geometry when doing boolean,
which is correct when used as a tool, but not when a modifier.
Added a "keep_hidden" argument to bmesh_boolean to distinguish the
two cases.
Also fixed a bug when the tool is used with hidden geometry that
is attached to unhidden geometry that is deleted by the operation.
Also added code so that exact solver does the whole collection at once.
This patch allows users to use a collection (as an alternative to Object)
for the boolean modifier operand, and therefore get rid of a long modifier stack.
With this option, self-intersections in either or both operands
will be handled properly (if both sides are piecewise winding
number constant, and maybe some other cases too).
In the Boolean tool, this flag was there already but the code
forced a unary operation in that case; this commit corrects it
to make a binary operation. This flag makes the code slower, which
is why it is an option and not an always-on thing.
This is for design task T67744, Boolean Redesign.
It adds a choice of solver to the Boolean modifier and the
Intersect (Boolean) and Intersect (Knife) tools.
The 'Fast' choice is the current Bmesh boolean.
The new 'Exact' choice is a more advanced algorithm that supports
overlapping geometry and uses more robust calculations, but is
slower than the Fast choice.
The default with this commit is set to 'Exact'. We can decide before
the 2.91 release whether or not this is the right choice, but this
choice now will get us more testing and feedback on the new code.
