React and WebAssembly to Rewrite Native Apps

Native Web Apps

@FlorianRival

 open-source, cross-platform game creator designed to be used by everyone

  • An editor for games
  • Visual programming
  • Output HTML5 games

The editor is getting old

  • Lots of cross-platforms issues with the UI toolkit, support for macOS and Linux is bad.
  • Iterating on the software is slow (C++ 😬)
  • Building UI is slow...
  • ...and limited to old UI components...
  • ...and UX would need some enhancements 😇
  • The entry barrier for new contributors is high (C++ 😬)

It's time to react!

Could web technologies help?

React is perfect for making complex UI

Well, really?...

Can we have

list and trees of hundreds of elements, 

dynamic panels,

2d/3d visualizations

nested dialogs,

color pickers, tabs, file trees, a "real app" feeling

drag'n'drop, search,

, copy-paste,

edit code in an editor...

Can we make ambitious apps?

2d/3d visualizations

, nested

JavaScript is perfect for most applications

Well, really?...

what if we

already have a native codebase?

Or have advanced

computations,

or need consistent perfs?

GUI (windows, dialogs...)

Filesystem

React.js powered interface

Node.js/browser adapters

X-platform toolkit (wxWidgets)

GDevelop C++ codebase

GDevelop C++ codebase

Core classes (game, scene, object, textures...)
Game exporter (JS "transpiler")
libGDevelop.js

JS

Writing WebAssembly

Using Emscripten

git clone https://github.com/emscripten-core/emsdk.git
cd emsdk && ./emsdk install latest && ./emsdk activate latest
./emcc tests/hello_world.c
node a.out.js

For large projects, Emscripten provides replacements that swap GCC or Clang by Emscripten in build system (automake, CMake...)

Expose existing classes

class Layout : public ObjectsContainer {
public:
  void setName(const gd::String & name_) { name = name_; };
  const gd::String & getName() { return name; };

  Object& insertObject(const Object& object, size_t position) { ... };
  Object& getObject(const gd::String& name) { ... };
}

Expose existing classes (2)

interface Layout {
  void setName([Const] DOMString name);
  [Const, Ref] DOMString getName();

  [Ref] Object insertObject([Ref] gdObject object, unsigned long pos);
  [Ref] Object getObject([Const] DOMString name);
}

"WebIDL" bindings for Emscripten WebIDL binder:

Use Emscripten classes

Module().then(gd => {
  const layout = new gd.Layout();
  layout.setName("My game level");
  const object = new gd.Object();
  object.setName("My character");
  layout.insertObject(object, 0);

  console.log(layout.getName()); // "My game level"
  console.log(object.getObject("My character")); // Returns a gd.Object
});
  • Converted, including JS strings (to char*)

Primitive types?

If I pass an object?

  • std::iostream is binded to console.log
  • Objects references are converted to pointers (or references) by the webIDL generated glue code

Can I debug?

Things to know

const layout = new gd.Layout();
// ...
gd.destroy(layout); // Binded objects need manual destruction
  • Memory management requires care!
> console.log(layout); 
{ ptr: 6804120 }

Wasm memory

The content of gd.Layout

  • For React:
componentDidMount() { this._project = new gd.Project(); }
componentWillUnmount() { gd.destroy(this._project); }

or use an Effect Hook 🔥

Things to know (2)

Output files can be large (~3mb for GDevelop),

but gzip helps (down to ~1mb).

Things to know (3)

  • A complete test set is invaluable for ensuring that no errors are in the bindings.
abort(16). Build with -s ASSERTIONS=1 for more info.
  • Wrong type for a parameter
  • Parameter forgotten
  • Using a deleted object

What can go wrong?

GUI (windows, dialogs...)

Filesystem

React.js powered interface

Node.js/browser adapters

GDevelop JS codebase

GDevelop C++ codebase

Core classes (game, scene, object, textures...)
Game exporter (JS "transpiler")
libGDevelop.js

Creating a complex UI?

Find a component library

  • Extensive list of high quality components
  • Good theming support
  • Accessibility
  • Documentation quality

Large lists (with drag'n'drop)

Virtualized lists

const ObjectsList = (props) => (
  <List
    rowRenderer={({ ... }) => {
      <ObjectRow ... />
    })
  />
);
const ObjectRow = () => <div>...</div>;
const ObjectsList = (props) => 
	props.map(group => <ObjectRow ... />)

react-dnd

react-virtualized

react-window

Panels/resizable editors

react-mosaic

Use a tiling window library

Large trees (with drag'n'drop)

Virtualization again!

react-sortable-tree

Levels rendering or visualizations

Forget the DOM

Don't forget the DOM

<svg
  onPointerMove={...}
  onPointerUp={...}
>
  <polygon
    stroke="rgba(255,0,0,0.5)"
    points={vertices.map(vertex =>
      `${vertex.getX()},${vertex.getY()}`
    ).join(' ')}
  />
  {vertices.map((vertex, j) => (
    <circle
      onPointerDown={...}
      key={`vertex-${j}`}
      fill="rgba(255,0,0,0.75)"
      cx={vertex.getX()}
      cy={vertex.getY()}
      r={5}
    />
  ))}
</svg>

When things aren't fast enough

Profile the rendering

Measure performance in production (React development build is way slower)

Inspect calls to WebAssembly

  • Beware of overhead in binding code/wasm call when calling functions, in particular if rendering large lists
objects // list.length === N
  .filter(object => {
    return object.getType() !== "";
  }) // N wasm calls + string conversions
  .map(object => {
    return object.getVariables(project)
  }); // N wasm calls + object conversions
  • It might be useful to store strings/values on the JS side if you know they won't change.

When your codebase is growing

Components for everything

<FlatButton style={{fontSize: 12}}>
  Help
</FlatButton>
<FlatButton>
  Help
</FlatButton>

😒

🙂

🤩

<HelpButton />

Avoid custom/adhoc styles, that won't scale:

Make a component for it! #DesignSystem

Don't unit test your visual components...

Well actually, do, but only for part where there is logic

...but create visual stories

Storybook

React Styleguidist

Use types

  • Will tell you that you (or someone else) forgot to pass/remove a prop

Flow

Typescript

  • Help auto-completion
  • Avoid most silly (or not so silly) mistakes
  • Help to "document" your objects

Types shine when you or someone else is refactoring some parts of the app

GUI (windows, dialogs...)

Filesystem

React.js powered interface

Node.js/browser adapters

GDevelop JS codebase

GDevelop C++ codebase

Core classes (game, scene, object, textures...)
Game exporter (JS "transpiler")
libGDevelop.js

Consider your packaging options

Progressive Web App

Electron (or nw.js)

Embed in a native app

Build over Electron/native APIs

GUI (windows, dialogs...)

Filesystem

React.js powered interface

Node.js/browser adapters

GDevelop JS codebase

GDevelop C++ codebase

Core classes (game, scene, object, textures...)
Game exporter (JS "transpiler")
libGDevelop.js

Result?

What are users saying?

Wow, what a difference a year can make 

but I have to admit, once you worked a bit with it, it could be really more productive on many aspects than GD4

Amazing how much easier and streamlined the engine has become

It works!

The native web app is better than the native app

Ultra fast iterations,

ultra fast testing,

near perfect cross-platform,

faster startup time,

auto updates,

more contributors,

"try it online",

tablets/phones port

Thanks! 🙂

@FlorianRival

gdevelop-app.com

github.com/4ian/GDevelop

Native Web Apps, version 2

By Florian Rival

Native Web Apps, version 2

React, useful modules from the ecosystem and WebAssembly to create ambitious apps. Patterns and tips for create scalable applications at a fast pace.

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