		# modelling-wasm

		## Description

		This sub-repo contains all of the code for the subdivision surface modeling tools. It is largely comprised of C++ code that is compiled to WebAssembly. The `web` folder is for prototyping / testing in an isolated environment.

		A subdivision surface is represented by the `spl::SubdivisionSurface` class. Internally, this class actually maintains two different, interlinked data structures. The first is a customized version of the `pmp::Surface_mesh` class. This class serves as the low-level, halfedge mesh representation. Any topological changes / edits are made on this data structure and then propagated to the second data structure, which is an `OpenSubdiv::Far::TopologyRefiner`. This is necessary because internally, OpenSubdiv uses its own custom representation to accelerate the mesh refinement process.

		While all of this "back-and-forth" cross-talk between different representations might seem like a lot of work (read: slow), it is actually quite optimized. We follow a similar procedure to the one titled "custom factory for direct conversion," outlined in the [OpenSubdiv documentation](https://graphics.pixar.com/opensubdiv/docs/far_overview.html). Basically, there is a custom "conversion" class in `conversion.h` that is specifically designed to convert a `pmp::Surface_mesh` instance into the equivalent OpenSubdiv data structure.

		## References

		- [Emscripten and Ninja](https://github.com/emscripten-core/emscripten/issues/10412)
		- [Emscripten and C++ Starter CMake Project](https://gist.github.com/WesThorburn/00c47b267a0e8c8431e06b14997778e4)
		- [OpenSubdiv Documentation](https://graphics.pixar.com/opensubdiv/docs/intro.html)

		## Dependencies

		Right now, this project has the following dependencies:

		- OpenSubdiv (C++)
		- PMP (C++)

		And for the prototype web app:

		- Three.js
		- OrbitControls (part of the Three.js `examples` folder)
		- BufferGeometryUtils (same as above)
		- TransformControls (same as above)

		OpenSubdiv and PMP are both submodules that must be initialized after cloning this repository (see notes below).

		## Installation

		Install the git submodules needed for this repo with: `git submodule update --init --recursive`. The only submodules at the moment are PMP and OpenSubdiv.

		#### MacOS

		You need to install Emscripten, cmake and Ninja build system:

		```sh
		brew install emscripten cmake ninja
		```

		#### Windows

		First, install Emscripten. Open the Emscripten command prompt (or `cmd` and run `emsdk_env.bat` to set up the necessary environment variables).

		Install Ninja (build system). Ensure that `ninja.exe` is in your `PATH`

		## Build

		Run `yarn build` or:

		- Create a folder called `build` inside this repository - navigate into this directory: `mkdir build && cd build`
		- Inside `build` run `emcmake cmake -G Ninja -DCMAKE_BUILD_TYPE=Release ..`
		- Next, run `cmake --build .` - this will generate a pair of `.wasm` + `.js` files in the `web` directory
		- Navigate into the `web` directory and start up an HTTP server: `python3 -m http.server`
		- Open your browser: `localhost:8000`
		- For convenience: if you already built the binary once and but changed something and want to quickly build again, you can from `packages/modelling-wasm/build` run `cd .. && rm -rf build && mkdir build && cd build && emcmake cmake -G Ninja -DCMAKE_BUILD_TYPE=Release .. && cmake --build . -jXX` where XX is should be less than the 2\*number of cores in your CPU.

		Note: for code completion in VS Code, make sure you install the "CMake" and "CMake Integration" addons.

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