metro VS yoga

For details on the implementation you can see Evan's PR to metro here.

Some development tools for the web are similar (Chrome debugger, mostly) to those for React Native, but other aspects are very different (working with the metro bundler, using Flipper, AsyncStorage debugging, more). Some techniques developers will use are the same (breakpoints and console logging), but others are different (knowing when to restart the packager vs reinstall the app on device).

We’re almost done with setting up the project. The last thing in the React Native app is to add watchFolders so metro knows where the linked node_modules are. The shared modules are symlinked by yarn, and since metro doesn’t follow symlinks we need to explicitly say it where the linked node_modules are.

Unfortunately it is what it is... I use intellij instead of webstorm since they're the same thing basically. I spent a shitton of time figuring out how to link a local package i was creating for my app only to discover about this issue that is almost as old as react native itself. (luckily there's rnx-kit that solves the problem). Not to talk about the impossibility to have one goddamn IDE to write both typescript, java and c++. Currently i have to write ts/js in intellij, then i have to switch to android studio to write java/c++.

React Native packager. Override instructions here.

React Native doesn't play nicely with most monorepo tools out of the box as Metro doesn't support symlinking.

Because React Native for Web is a React website, you can use front-end tools to build and run it. For example, you can build it with Webpack or Rollup instead of Metro bundler.

Before we can run the app, we still need do one more thing: make metro bundler compatible with Yarn workspaces' hoisting.

Second, sharing code with other projects (e.g., backend code, web apps) may get complicated. Out-of-the-box, React Native's metro bundler cannot reference code outside of the project's root directory. You can configure it to do so (and we'll do it as well later on). Still, once you do it, you'll also need to ensure dependencies resolution works correctly (to avoid loading two different versions of the same library, for example); which might not be as easy as it may sound.

We still wanted to leverage a layout engine that could be performant and easy-to-use. After doing some performance testing with native UIKit, Autolayout, and a few other third-party options, we ended up bringing FlexLayout into the mix, which is a Swift implementation of Facebook’s Yoga layout engine. All RPL components utilize FlexLayout in order to lay out content fast and efficiently. While we’ve enjoyed using it, we’ve found a few touch points to be mindful of. There are some rough edges we’ve found, such as utilizing stack views with subviews that use FlexLayout, that often come at odds with both UIKit and FlexLayout’s layout engines.

We have our own test suite (orginally derived from the test suite of Meta's Yoga layout library [0]) which consists of text fixtures that are small HTML snippets [1] and a test harness [2] that turns those into runnable tests, utilising headless chrome both to parse the HTML and to generate the assertions based on the layout that Chrome renders (so we are effectively comparing our implementation against Chrome). We currently have 686 generated tests (covering both Flexbox and CSS Grid).

We would like to utilise the Web Platform Test suite [3], however these are not in a standard format and many of the tests require JavaScript so we are not currently able to do that.

[0]: https://github.com/facebook/yoga

[1]: https://github.com/DioxusLabs/taffy/tree/main/test_fixtures

[2]: https://github.com/DioxusLabs/taffy/tree/main/scripts/gentes...

[3]: https://github.com/web-platform-tests/wpt/tree/master/css/cs...

The "engine" is built on top of amazing https://www.lwjgl.org/ and https://github.com/bkaradzic/bgfx/, and UI system is baked by https://github.com/memononen/nanovg and https://github.com/facebook/yoga

React Native uses the Yoga engine under the hood, which allows you to use CSS properties to layout your React Native UI in a way that translates really well. Layout in Yoga is limited to Flexbox and absolute/relative positioning, however; there is no CSS grid and no display attribute. This keeps things simpler and more performant, but if developers are accustomed to using other layout techniques on the web, they’ll need to adjust to this new limitation.

PR #246 is super interesting to check out: by fixing the caching strategy, we were able to eliminate an exponential time (with respect to tree depth) performance penalty, and get comparable speeds for flat and deeply nested layouts (something I'd never expected to be possible). Preliminary benchmarks shows us significantly faster than yoga, Meta's C++ library for the same thing, especially on deep trees. Not too shabby for a tiny team of volunteers!

You're going to build the CLI using Ink, a React component-based library for building interactive CLIs. It uses Yoga to build Flexbox layouts in the terminal, so most CSS-like props are available in Ink as well. Ink is simply a React renderer for the terminal, so all the React features are supported. No need to learn a new syntax specific to Ink.

Interesting.

I was thinking that this was going to be a crazy amount of layout engine work, but now I look a little closer it appears the layout work is farmed out to yoga [0] (not trying to take away anything from the effort here). So this project is almost a wrapper around running yoga as a renderer and using SVG as a form of backend target?

I say "appears" because the yoga landing page doesn't do a great job of explaining what it does.

[0] https://github.com/facebook/yoga