Mesh Differencing
A feature that I’ve long wanted in Madeup is the ability to subtract away holes from a mesh. I try to implement most features myself, because I want to learn. However, constructive solid geometry is too much for me. I turned to libigl, CGAL, Eigen, and Boost for help, and now I can join solids in interesting ways. The first three things I made? A car body with holes for the axles, a spring-loaded hand cannon with holes for a locking pin, and the requisite six-sided die.
I’m still tweaking the first two, but to commemorate the moment, I’ll share the d6. It was made by creating a cube using the box solidifier and then visiting all the pips as nodes for the spheres solidifier. The difference mesh is computed as die - pips. (Union and intersection are expressed using or and and, respectively.)
A d6, which is a cube minus 21 hemispheres.
/usr/lib/ruby/2.7.0/rubygems/dependency.rb:311:in `to_specs': Could not find 'coderay' (>= 0) among 56 total gem(s) (Gem::MissingSpecError) Checked in 'GEM_PATH=/.gem/ruby/2.7.0:/var/lib/gems/2.7.0:/usr/lib/ruby/gems/2.7.0:/usr/share/rubygems-integration/2.7.0:/usr/share/rubygems-integration/all:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.7.0:/home/johnch/.gems', execute `gem env` for more information from /usr/lib/ruby/2.7.0/rubygems/dependency.rb:323:in `to_spec' from /usr/lib/ruby/2.7.0/rubygems/core_ext/kernel_gem.rb:62:in `gem' from ./coderay:24:in `'
I didn’t have a real d6 in front of me (the Internet doesn’t count), so I guessed on the face arrangement. It looks like I was wrong. 1 opposes 6, 5 opposes 2, and 3 opposes 4. I hadn’t realized before that opposite faces sum to 7.
The pips should be black, shouldn’t they? Sadly, I don’t think libigl preserves vertex metadata when applying boolean operations between meshes, so coloring them differently seems like a job better suited for a mouse-based modeling program.