# CAD reader for johnmcm.com

The engine behind johnmcm.com's STEP & IGES Viewer (/step-viewer).

It is [occt-import-js](https://github.com/kovacsv/occt-import-js) 0.0.23 by
Viktor Kovacs: [Open CASCADE Technology](https://dev.opencascade.org) compiled
to WebAssembly with Emscripten. Both are LGPL-2.1 (OCCT with the Open CASCADE
exception); the licence texts are `LICENSE` (occt-import-js) and
`LICENSE.occt`.

- The WebAssembly module, `occt-import-js.wasm`, is used exactly as published
  on npm.
- The JavaScript loader, `occt-import-js.js`, is patched by `patch.mjs`. Its
  embind layer builds the wrappers between JavaScript and C++ by generating
  source text and compiling it with `new Function`, which this site's Content
  Security Policy does not allow. `patch.mjs` rewrites the two functions that
  do that (`craftInvokerFunction` and `__emval_get_method_caller`) as plain
  closures doing the same steps, as Emscripten does when built with
  `-sDYNAMIC_EXECUTION=0`. Nothing else is changed.

To rebuild, run `node wasm-src/occt/patch.mjs` from `frontend/`. It downloads
the npm file, checks its hash, patches it and writes
`frontend/vendor/local/occt@1/`. The page loads the loader and the module as
separate files, so either can be replaced with one built from modified source.