An anonymous reader writes "A few months after releasing support for viewing models in .STL format, GitHub just added support for viewing changes to .STL formatted 3D models directly in the browser. 'How does this work? We take both versions of the model, and using binary space partitioning, we compute the added, removed, and unchanged parts. This is done using csgtool, a C library paired with a Ruby gem via FFI. These pieces are cached and displayed by the 3D viewer we already have, though we color them differently and play with their transparency to help illustrate the changes.'"