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@yostane

#TechAtWorldline

Yassine

Benabbas

DevRel / Teacher

Video game collector

😍 Kotlin, WASM, or any fancy technology

We design payments technology that powers the growth of millions of businesses around the world.

Managing 43+ billion transactions per year

7000+ engineers in over 40 countries

#TechAtWorldline

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blog.worldline.tech

Web Assembly (WASM)

  • Portable binary instruction format
  • "Initially" targeted for web browsers (to speed up JS)
(module
  (func (result i32)
    (i32.const 42)
  )
  (export "getUniversalNumber" (func 0))
)

00 61 73 6d 01 00 00 00  01 05 01 60 00 01 7f 03  |.asm.......`....|
02 01 00 07 16 01 12 67  65 74 55 6e 69 76 65 72  |.......getUniver|
73 61 6c 4e 75 6d 62 65  72 00 00 0a 06 01 04 00  |salNumber.......|
41 2a 0b 00 0a 04 6e 61  6d 65 02 03 01 00 00     |A*....name.....|

wat format (human readable)

wasm file

https://github.com/WebAssembly/wabt

Browser

Compiler

WASM runtime

JS engine

Based on: https://wasmlabs.dev/articles/docker-without-containers/

binary

WASM in browsers

Source code

Browser

Compiler

WASM runtime

JS engine

Based on: https://wasmlabs.dev/articles/docker-without-containers/

binary

WASM in browsers

Source code

Browser

Compiler

WASM runtime

JS engine

Based on: https://wasmlabs.dev/articles/docker-without-containers/

binary

WASM in browsers

Source code

WASM on the browser

  • A lot of languages compile to WASM
  • JS interop

Need to do something related to WASM

.NET on the browser

  • .NET: C# OSS cross-platform framework
  • Compiles to WASM (Blazor is an example)
  • API to interop with JS
public partial class MyClass
{
    [JSExport]
    internal static string Greeting()
    {
        var text = $"Hello, {GetHRef()}";
        Console.WriteLine(text);
        return text;
    }

    [JSImport("window.location.href", "main.js")]
    internal static partial string GetHRef();
}
setModuleImports('main.js', {
    window: {
        location: {
            href: () => globalThis.window.location.href
        }
    }
});

const text = exports.MyClass.Greeting();
console.log(text);

.NET 7+

JS Interop

Let's port a .NET game !

Game porting

  • Make a game run in platforms other than its original ones
  • By rewriting / adapting the source code for the new platform(s)
  • Not porting: virtual machine or emulator

MVG's video is a great source of inspiration

  • Released in 1993 for DOS
  • Has two parts:
    • engine: Game logic + I/O
    • WAD file: all assets and maps

🌟 Doom is portable by design 🌟

http://mrglitchsreviews.blogspot.com/2012/09/doom-console-ports.html

Ported to a LOT of platforms

25 official licensed ports https://www.thegamer.com/doom-how-many-platforms-ports-consoles

https://www.link-cable.com/top-10-weird-doom-ports/

Source: https://www.yahoo.com/news/1995-bill-gates-gave-crazy-180900044.html

ManagedDoom

  • .NET Port of LinuxDoom (official source code)
  • ManagedDoom V1 Uses SFML (graphics + audio + input)
    • V2 uses silk.net (released 27 Dec 2022)
  • My work is a fork of ManagedDoom V1

id-Software/DOOM

sinshu/managed-doom

yostane/MangedDoom-Blazor

Game loop in C#

while (waitForNextFrame()){
  const input = getPlayerInput();
  const { frame, audio } 
  	      = UpdateGameState(input, WAD);
  render(frame);
  play(audio);
}

Game loop in JS

function gameLoop(){
  if (canAdvanceFrame()){
    const input = getPlayerInput();
    const { frame, audio } 
  	      = UpdateGameState(input, WAD);
    render(frame);
    play(audio);
  }
  requestAnimationFrame(gameLoop);
}
requestAnimationFrame(gameLoop);

ManagedDoom V1 architecture

For loop (game loop)

pressed keys (keyup)

release keys (keydown)

['Z', 'Q']

['space']

Frame buffer

Audio buffer

SFML Audio

SFML Video

 1 iteration of the Doom Engine

Updates the game state

.NET WASM

~70% OK

.NET WASM

wad

DOOM.wad

sf2

SoundFont.sf2

Blazor Doom architecture

pressed keys (keyup)

release keys (keydown)

['Z', 'Q']

['space']

wad

DOOM.wad

requestAnimationFrame

Run .Net

Audio buffer

Frame buffer

Canvas

Audio Context

Run JS

Run JS

 1 iteration of the Doom Engine

Updates the game state

sf2

SoundFont.sf2

Porting strategy

  • Clone sinshu/managed-doom and compile to .NET WASM
  • Reverse engineer SFML:
    • Put empty implementations where it fails and matk them ("TODO: implement")
    • Implement little by little using guesswork and logic
    • Delegate to JS when necessary

creator.nightcafe.studio

using SFML.Audio; // Not available

namespace ManagedDoom.Audio
{
    public sealed class SfmlSound : ISound, IDisposable
    {
        private SoundBuffer[] buffers;
    }
}

Example:

SFML.Audio.SoundBuffer

is not available

namespace SFML.Audio
{
    public class SoundBuffer
    {
        public SoundBuffer(short[] samples, int v, uint sampleRate)
        {
        	// TODO: implement
        }

        internal void Dispose()
        {
            // TODO: implement
        }
    }
}

So, let's reverse-engineer it

namespace SFML.Audio
{
    public class SoundBuffer
    {
        public short[] samples;
        private int v;
        public uint sampleRate;

        public SoundBuffer(short[] samples, int v, uint sampleRate)
        {
            this.samples = samples;
            this.v = v;
            this.sampleRate = sampleRate;
        }

        public Time Duration { get; internal set; }

        internal void Dispose()
        {
            // TODO: implement
        }
    }
}
<html>
  <head>
    <!-- Sets .Net interop and starts the game loop -->
    <script type="module" src="./main.js"></script>
   </head>
  <body>
  	<canvas id="canvas" width="320" height="200" 
            style="image-rendering: pixelated" />
  </body>
</html>

Entry point

Running the gameloop

main.js

import { dotnet } from "./dotnet.js";
const { getAssemblyExports, getConfig } = await dotnet.create();
const exports = await getAssemblyExports(getConfig().mainAssemblyName);
await dotnet.run();

function gameLoop(timestamp) {
    if (timestamp - lastFrameTimestamp >= 1000 / 30) {
      	lastFrameTimestamp = timestamp;
        exports.BlazorDoom.MainJS.UpdateGameState(keys);
    }
    requestAnimationFrame(gameLoop);
}

Running the gameloop

main.js

public partial class MainJS // this name is required
{
  public static void Main()
  {
    app = new ManagedDoom.DoomApplication();
  }
  
  [JSExport] // Can be imported from JS
  public static void UpdateGameState(int[] keys)
  { // computes the next frame and sounds
     managedDoom.UpdateGameState(keys); 
  }
}
import { dotnet } from "./dotnet.js";
const { getAssemblyExports, getConfig } = await dotnet.create();
const exports = await getAssemblyExports(getConfig().mainAssemblyName);
await dotnet.run();

function gameLoop(timestamp) {
    if (timestamp - lastFrameTimestamp >= 1000 / 30) {
      	lastFrameTimestamp = timestamp;
        exports.BlazorDoom.MainJS.UpdateGameState(keys);
    }
    requestAnimationFrame(gameLoop);
}

Audio playback

0.5 1 0.75 0 -0.75 -1 -0.5 0

https://developer.mozilla.org/en-US/docs/Web/Media/Formats/Audio_concepts

AudioContext

Sample

1 / Sampling frequency

+ Sampling frequency

🔊

Audio playback

void PlayCurrentFrameSound(SoundBuffer soundBuffer)
{
	int[] samples = Array.ConvertAll(soundBuffer.samples, Convert.ToInt32);
	BlazorDoom.Renderer.playSoundOnJS(samples, (int)soundBuffer.sampleRate);
}
namespace BlazorDoom
{
    [SupportedOSPlatform("browser")]
    public partial class Renderer
    {
        [JSImport("playSound", "blazorDoom/renderer.js")]
        internal static partial string playSoundOnJS(
        	int[] samples, 
            int sampleRate
        );
    }
}

Audio playback

export function playSound(samples, sampleRate) {
    audioContext = new AudioContext({
        sampleRate: sampleRate,
    });
    const length = samples.length;
    const audioBuffer = audioContext.createBuffer(
        1,
        length,
        sampleRate
    );

    var channelData = audioBuffer.getChannelData(0);
    for (let i = 0; i < length; i++) {
        // noralize the sample to be between -1 and 1
        channelData[i] = samples[i] / 0xffff;
    }

    var source = audioContext.createBufferSource();
    source.buffer = audioBuffer;
    source.connect(audioContext.destination);
    source.start();
}
0 1 2 3 1 1 2 3
0 1 2 3

From 1D frame to a 2D frame

2 2 0 1

Frame data

 12 bytes

Color palette

Canvas Frame

12 * 4 bytes (r, g, b, a)

  • Doom uses color indexing

  • Image built from top to bottom and from left to right

Frame rendering: from C# to JS

namespace BlazorDoom
{
    [SupportedOSPlatform("browser")]
    public partial class Renderer
    {
        [JSImport("drawOnCanvas", "blazorDoom/renderer.js")]
        internal static partial string renderOnJS(byte[] screenData,
                                                   int[] colors);
    }
}
export function drawOnCanvas(screenData, colors) {
  // 
}
public class DoomRenderer
{
  // Called by updateGameState
  private void Display(uint[] colors)
  {
    BlazorDoom.Renderer.renderOnJS(screen.Data, (int[])((object)colors));
  }
}

Rendering a Frame buffer

export function drawOnCanvas(screenData, colors) {
  	const context = getCanvas().context;
    const imageData = context.createImageData(320, 200);
    let y = 0;
    let x = 0;
    for (let i = 0; i < screenData.length; i += 1) {
        const dataIndex = (y * width + x) * 4;
        setSinglePixel(imageData, dataIndex, colors, screenData[i]);
        if (y >= height - 1) {
            y = 0;
            x += 1;
        } else {
            y += 1;
        }
    }
    context.putImageData(imageData, 0, 0);
}

function setSinglePixel(imageData, dataIndex, colors, colorIndex) {
    const color = colors[colorIndex];
    imageData.data[dataIndex] = color & 0xff; // R 
    imageData.data[dataIndex + 1] = (color >> 8) & 0xff; // G
    imageData.data[dataIndex + 2] = (color >> 16) & 0xff; // B
    imageData.data[dataIndex + 3] = 255; // Alpha
}

Key takeaways

  • WASM possibilities are limitless
  • Porting a game is way to learn programming while having fun

@yostane

Yassine

Benabbas

Links

  • https://mspoweruser.com/this-doom-digital-camera-source-port-is-amazing-and-bizarre/
  • https://www.link-cable.com/top-10-weird-doom-ports/
  • pixabay.com
  •  Doom text generator: https://c.eev.ee/doom-text-generator 

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