Some of you reading this are very experienced with opening up windows in Rust and probably have your favorite windowing library, but this guide is designed for everybody, so it's something that we need to cover. Luckily, you don't need to read this if you know what you're doing. One thing that you do need to know is that whatever windowing solution you use needs to support the [raw-window-handle](https://github.com/rust-windowing/raw-window-handle) crate.
As of version 0.10, wgpu requires Cargo's [newest feature resolver](https://doc.rust-lang.org/cargo/reference/resolver.html#feature-resolver-version-2), which is the default in the 2021 edition (any new project started with Rust version 1.56.0 or newer). However, if you are still using the 2018 edition, you must include `resolver = "2"` in either the `[package]` section of `Cargo.toml` if you are working on a single crate or the `[workspace]` section of the root `Cargo.toml` in a workspace.
All this does is create a window and keep it open until the user closes it or presses escape. Next, we'll need a `main.rs` to run the code. It's quite simple. It just imports `run()` and, well, runs it!
If I go through this tutorial about WebGPU and never talk about using it on the web, then I'd hardly call this tutorial complete. Fortunately, getting a wgpu application running in a browser is not too difficult once you get things set up.
These lines tell Cargo that we want to allow our crate to build a native Rust static library (rlib) and a C/C++ compatible library (cdylib). We need rlib if we want to run wgpu in a desktop environment. We need cdylib to create the Web Assembly that the browser will run.
Web Assembly, i.e. WASM, is a binary format supported by most modern browsers that allows lower-level languages such as Rust to run on a web page. This allows us to write the bulk of our application in Rust and use a few lines of Javascript to get it running in a web browser.
The `[target.'cfg(target_arch = "wasm32")'.dependencies]` line tells Cargo to only include these dependencies if we are targeting the `wasm32` architecture. The next few dependencies just make interfacing with JavaScript a lot easier.
* [console_error_panic_hook](https://docs.rs/console_error_panic_hook) configures the `panic!` macro to send errors to the javascript console. Without this, when you encounter panics, you'll be left in the dark about what caused them.
* [console_log](https://docs.rs/console_log) implements the [log](https://docs.rs/log) API. It sends all logs to the javascript console. It can be configured to only send logs of a particular log level. This is also great for debugging.
* We need to enable the WebGL feature on wgpu if we want to run on most current browsers. Support is in the works for using the WebGPU api directly, but that is only possible on experimental versions of browsers such as Firefox Nightly and Chrome Canary.<br>
You're welcome to test this code on these browsers (and the wgpu devs would appreciate it as well), but for the sake of simplicity, I'm going to stick to using the WebGL feature until the WebGPU api gets to a more stable state.<br>
If you want more details, check out the guide for compiling for the web on [wgpu's repo](https://github.com/gfx-rs/wgpu/wiki/Running-on-the-Web-with-WebGPU-and-WebGL)
* [wasm-bindgen](https://docs.rs/wasm-bindgen) is the most important dependency in this list. It's responsible for generating the boilerplate code that will tell the browser how to use our crate. It also allows us to expose methods in Rust that can be used in JavaScript and vice-versa.<br>
I won't get into the specifics of wasm-bindgen, so if you need a primer (or just a refresher), check out [this](https://rustwasm.github.io/wasm-bindgen/)
* [web-sys](https://docs.rs/web-sys) is a crate with many methods and structures available in a normal javascript application: `get_element_by_id`, `append_child`. The features listed are only the bare minimum of what we need currently.
Then, we need to toggle what logger we are using based on whether we are in WASM land or not. Add the following to the top of the run function, replacing the `env_logger::init()` line:
This will set up `console_log` and `console_error_panic_hook` in a web build and will initialize `env_logger` in a normal build. This is important as `env_logger` doesn't support Web Assembly at the moment.
The `"wasm-example"` id is specific to my project (aka. this tutorial). You can substitute this for whatever id you're using in your HTML. Alternatively, you could add the canvas directly to the `<body>` as they do in the wgpu repo. This part is ultimately up to you.
Now you can build a wgpu application with just wasm-bindgen, but I ran into some issues doing that. For one, you need to install wasm-bindgen on your computer as well as include it as a dependency. The version you install as a dependency **needs** to exactly match the version you installed. Otherwise, your build will fail.
To get around this shortcoming and to make the lives of everyone reading this easier, I opted to add [wasm-pack](https://rustwasm.github.io/docs/wasm-pack/) to the mix. Wasm-pack handles installing the correct version of wasm-bindgen for you, and it supports building for different types of web targets as well: browser, NodeJS, and bundlers such as webpack.
Once you've done that, we can use it to build our crate. If you only have one crate in your project, you can just use `wasm-pack build`. If you're using a workspace, you'll have to specify what crate you want to build. Imagine your crate is a directory called `game`. You would then use:
Once wasm-pack is done building, you'll have a `pkg` directory in the same directory as your crate. This has all the javascript code needed to run the WASM code. You'd then import the WASM module in javascript:
This site uses [Vuepress](https://vuepress.vuejs.org/), so I load the WASM in a Vue component. How you handle your WASM will depend on what you want to do. If you want to check out how I'm doing things, take a look at [this](https://github.com/sotrh/learn-wgpu/blob/master/docs/.vuepress/components/WasmExample.vue).