Let's Build a Cross-platform 3D Engine with Kotlin/Multiplatform

When creating a game, you want your game to be available on all platforms to target as many players as possible. Developing a game engine is a challenge: you have to deal with mathematical concepts, animations, player interactions... Creating an engine that runs on different platforms is even more challenging. Is Kotlin and Kotlin/Multiplatform could be the right tool to build this kind of engine? Let's check this out together.

Message for you, so you can already be aware what you can expect from this session:
Using existing Java game engines, you can create a game that runs on the JVM, in a browser or on Android and iOS. But it requires some complex tooling, when tools are available for the platform you're targeting.

This session is about the creation of a game engine that runs the same way in a browser, in a JVM, on iOS or Android.

(Conference For Kotliners - 05/06/2020 - Online)

Transcript

1. LET'S BUILD A CROSS
   PLATFORM 3D ENGINE
   WITH KOTLIN/MULTIPLATFORM
   

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2. David
   Wursteisen
   

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3. "#$%&'($#&
   

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4. John Carmack
   

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8. Game 

   development
   Kotlin
   Multiplatform
   

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9. You, at the end of 

   this conference
   Game 

   development
   Kotlin
   Multiplatform
   

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10. GAME
    DEVELOPMENT
    

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16. public void render(float delta) {

    movePlayer(delta);

    moveEnemies(delta);

    moveWorld(delta);

    

    renderWorld();

    renderEnemies();

    renderPlayer();

    }
    

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17. public void render(float delta) {

    movePlayer(delta);

    moveEnemies(delta);

    moveWorld(delta);

    

    renderWorld();

    renderEnemies();

    renderPlayer();

    }
    

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18. public void render(float delta) {

    movePlayer(delta);

    moveEnemies(delta);

    moveWorld(delta);

    

    renderWorld();

    renderEnemies();

    renderPlayer();

    }
    

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19. public void render(float delta) {

    movePlayer(delta);

    moveEnemies(delta);

    moveWorld(delta);

    

    renderWorld();

    renderEnemies();

    renderPlayer();

    }
    60x

    seconds
    

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20. (0,0)
    x
    y
    

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21. PICKING A GAME ENGINE
    

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23. ❤
    

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25. Hair Dash - http://cleancutgames.com/
    

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29. Core
    iOS
    GWT
    Android
    Desktop
    
    
    

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30. View Slide

31. Hi all.
    My studio, Sickhead, did the port of Slay the Spire to Switch.
    We struggled for a bit trying to convert the Java to C++ code directly using existing third party
    tools. The resulting C++ code pretty much didn't work at all and took tons of manual changes to
    make work. After several months of failure taking that path we changed gears.
    We instead converted Java to C# which required much less manual fixes to make work and solved
    all the GC memory management issues. This means we had a C# version of LibGDX in there as
    well as all the game code. We then just added a new LibGDC backend with new OpenGL bindings
    and new sound, input implementations. At that point we had a PC port of Spire using C#.
    We then used our own mature C# IL to C++ cross compiler and runtime we developed to port XNA
    and MonoGame titles to generate binaries which run on Switch, PS4, XB1, and other platforms.
    While Java -> C# -> C++ was a crazy idea when we started... it actually works beautifully and
    makes perfect sense now.
    HTTPS://WWW.BADLOGICGAMES.COM/FORUM/VIEWTOPIC.PHP?F=11&T=29625
    

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32. Hi all.
    My studio, Sickhead, did the port of Slay the Spire to Switch.
    We struggled for a bit trying to convert the Java to C++ code directly using existing third party
    tools. The resulting C++ code pretty much didn't work at all and took tons of manual changes to
    make work. After several months of failure taking that path we changed gears.
    We instead converted Java to C# which required much less manual fixes to make work and solved
    all the GC memory management issues. This means we had a C# version of LibGDX in there as
    well as all the game code. We then just added a new LibGDC backend with new OpenGL bindings
    and new sound, input implementations. At that point we had a PC port of Spire using C#.
    We then used our own mature C# IL to C++ cross compiler and runtime we developed to port XNA
    and MonoGame titles to generate binaries which run on Switch, PS4, XB1, and other platforms.
    While Java -> C# -> C++ was a crazy idea when we started... it actually works beautifully and
    makes perfect sense now.
    HTTPS://WWW.BADLOGICGAMES.COM/FORUM/VIEWTOPIC.PHP?F=11&T=29625
    MY STUDIO, SICKHEAD, 

    DID THE PORT OF SLAY THE SPIRE TO SWITCH.

    WHILE JAVA -> C# -> C++ WAS A CRAZY IDEA
    WHEN WE STARTED... IT ACTUALLY WORKS
    BEAUTIFULLY AND MAKES PERFECT SENSE NOW.
    

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33. KOTLIN
    MULTIPLATFORM
    FEEDBACK LOOP
    

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34. LET'S DIVE IN
    BUILDING A 3D ENGINE
    

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35. void render(float delta) {
    }
    

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36. fun render(delta: float) {
    }
    

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37. KOTLIN/MULTIPLATFOM
    KOTLIN/JVM
    KOTLIN/NATIVE
    KOTLIN/JS
    KOTLIN/ANDROID
    

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38. Common
    Js
    Native
    Android
    Jvm
    

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39. KOTLIN/JVM KOTLIN/JS
    KOTLIN/ANDROID KOTLIN/NATIVE
    COMMON
    LIBGDX LIBGDX PLAYCANVAS RAYLIB
    

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40. JS NATIVE JVM
    

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41. KOTLIN/NATIVE
    KOTLIN/JS
    *.H CINTEROP *.KT
    *.D.TS DUKAT *.KT
    

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42. external open class ScrollbarComponentSystem(app: pc.Application) : ComponentSystem {
    override fun on(name: String, callback: HandleEvent, scope: Any): EventHandler
    override fun off(name: String, callback: HandleEvent, scope: Any): EventHandler
    override fun fire(name: Any, arg1: Any, arg2: Any, arg3: Any, arg4: Any): EventHandler
    override fun once(name: String, callback: HandleEvent, scope: Any): EventHandler
    override fun hasEvent(name: String): Boolean
    }
    

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43. external interface `T$8` {
    var volume: Number?
    get() = definedExternally
    set(value) = definedExternally
    var pitch: Number?
    get() = definedExternally
    set(value) = definedExternally
    var loop: Boolean?
    get() = definedExternally
    set(value) = definedExternally
    )
    

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46. OpenGL
    

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49. View Slide

50. OpenGL ES was deprecated in iOS 12.
    

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51. View Slide

52. VERTEX
    VERTEX
    VERTEX
    

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53. HTTPS://WWW.LABRI.FR/PERSO/NROUGIER/PYTHON-OPENGL/#MODERN-OPENGL
    VERTICES
    VERTEX

    SHADER
    FRAGMENT

    SHADER
    OpenGL (GPU)
    Kotlin (CPU)
    

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54. void main() {

    vec4 sum = vec4(0);

    

    float step = iResolution.y;

    // y

    for(float i = -area ; i <= area ; i += 1.) {

    // x

    for(float j = -area ; j <= area ; j += 1.) {

    float x = v_texCoords.x + i / iResolution.x;

    float y = v_texCoords.y + j / iResolution.y;

    sum += texture2D(u_texture, vec2(x, y)) * 0.005;

    }

    }

    gl_FragColor = texture2D(u_texture, v_texCoords) + sum;

    }
    OpenGL Shading Language (GLSL)
    

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59. BUILDING A 3D ENGINE
    BASED ON OpenGL
    

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60. KOTLIN/JVM KOTLIN/JS
    KOTLIN/ANDROID KOTLIN/NATIVE
    COMMON
    LWJGL OpenGL ES WebGL OpenGL
    

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61. WHAT YOU EXPECT
    

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62. WHAT YOU'LL GET
    

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64. A SHORT HIKE
    

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65. class GameExample : Game {
    override fun render(delta: Float) {
    }
    }
    Unit ?
    

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66. typealias Seconds = Float
    class GameExample : Game {
    override fun render(delta: Seconds) {
    }
    }
    

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67. interface CanMove {
    fun rotateX(angle: Float): CanMove
    }
    Radian or Degree ?
    

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68. typealias Degree = Float
    interface CanMove {
    fun rotateX(angle: Degree): CanMove
    }
    

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69. Y
    X
    Z
    

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70. 1. Translation
    2. Rotation
    3. Scale
    

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71. MATRIX
    

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72. MATRIX
    [ 1 | 0 | 0 | 0 ]

    [ 0 | 1 | 0 | 0 ]

    [ 0 | 0 | 1 | 0 ]

    [ 0 | 0 | 0 | 1 ]
    

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73. Scale
    MATRIX
    [ 1 | 0 | 0 | 0 ]

    [ 0 | 1 | 0 | 0 ]

    [ 0 | 0 | 1 | 0 ]

    [ 0 | 0 | 0 | 1 ]
    X
    Z
    Y
    Translation
    Rotation
    

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74. TRANSFORMATION = IDENTITY
    

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75. TRANSFORMATION = IDENTITY * TRANSLATION
    

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76. TRANSFORMATION = IDENTITY * TRANSLATION * TRANSLATION
    

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77. TRANSFORMATION = IDENTITY * TRANSLATION * TRANSLATION * ROTATION
    

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79. HTTPS://WWW.YOUTUBE.COM/WATCH?V=LJYDCYP0WG4
    

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80. data class Mat4(…) {
    // ...
    operator fun times(m: Mat4): Mat4 {
    val t = transpose(this)
    return Mat4(
    Float4(dot(t.x, m.x), dot(t.y, m.x), dot(t.z, m.x), dot(t.w, m.x)),
    Float4(dot(t.x, m.y), dot(t.y, m.y), dot(t.z, m.y), dot(t.w, m.y)),
    Float4(dot(t.x, m.z), dot(t.y, m.z), dot(t.z, m.z), dot(t.w, m.z)),
    Float4(dot(t.x, m.w), dot(t.y, m.w), dot(t.z, m.w), dot(t.w, m.w))
    )
    }
    }
    

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81. val result: Mat4 = Mat4(…) * Mat4(…)
    

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82. MATRIX
    [ 1 | 0 | 0 | 0 ]

    [ 0 | 1 | 0 | 0 ]

    [ 0 | 0 | 1 | 0 ]

    [ 0 | 0 | 0 | 1 ]
    How to access it?
    

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83. val mat: Mat4 = …
    val x = mat[0][4]
    val y = mat[1][4]
    val z = mat[2][4]
    

    

    
    

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84. data class Mat4(…) {
    // ...
    inline val scale: Float3
    get() = …
    inline val translation: Float3
    get() = …
    val rotation: Float3
    get() {
    …
    }
    }
    

    

    
    

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85. data class Float3(var x: Float = 0.0f, var y: Float = 0.0f, var z: Float = 0.0f) {
    inline var r: Float
    get() = x
    set(value) {
    x = value
    }
    inline var g: Float
    get() = y
    set(value) {
    y = value
    }
    inline var b: Float
    get() = z
    set(value) {
    z = value
    }
    }
    

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86. data class Mat4(…) {
    // ...
    inline val scale: Float3
    get() = …
    inline val translation: Float3
    get() = …
    val rotation: Float3
    get() {
    …
    }
    }
    

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87. data class Float3(
    var x: Float = 0.0f,
    var y: Float = 0.0f,
    var z: Float = 0.0f)
    val translation: Float3 = mat4.translation
    val (x, y, z) = translation
    

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88. CONVERTING
    INTO MULTIPLATFORM
    

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89. plugins {
    kotlin("multiplatform") version "1.3.60"
    }
    kotlin {
    js { }
    jvm { }
    sourceSets {
    val commonMain by getting {
    dependencies { implementation(kotlin("stdlib-common")) }
    }
    js().compilations["main"].defaultSourceSet {
    dependencies { implementation(kotlin("stdlib-js")) }
    }
    jvm().compilations["main"].defaultSourceSet {
    dependencies { implementation(kotlin("stdlib-jdk8")) }
    }
    }
    }
    

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90. inline fun pow(x: Float, y: Float) = StrictMath.pow(
    x.toDouble(),
    y.toDouble()
    ).toFloat()
    inline fun pow(x: Float, y: Float) = x.pow(y)
    java.lang.StrictMath
    

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91. KOTLIN-MATH.JAR (JVM)
    KOTLIN-MATH.JS (JS)
    KOTLIN-MATH.KLIB (NATIVE)
    

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92. BUILDING FOR
    MULTIPLATFORM
    

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93. interface GL {
    fun uniform1i(uniform: Uniform, data: Int)
    fun uniform2f(uniform: Uniform, first: Float, second: Float)
    fun uniform3f(uniform: Uniform, first: Float, second: Float, third: Float)
    // …
    }
    class WebGL(private val gl: WebGLRenderingContext) : GL {
    override fun uniform1i(uniform: Uniform, data: Int) {
    gl.uniform1i(uniform.uniformLocation, data)
    }
    override fun uniform2f(uniform: Uniform, first: Float, second: Float) {
    gl.uniform2f(uniform.uniformLocation, first, second)
    }
    override fun uniform3f(uniform: Uniform, first: Float, second: Float, third: Float) {
    gl.uniform3f(uniform.uniformLocation, first, second, third)
    }
    }
    COMMON
    

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94. interface GL {
    fun uniform1i(uniform: Uniform, data: Int)
    fun uniform2f(uniform: Uniform, first: Float, second: Float)
    fun uniform3f(uniform: Uniform, first: Float, second: Float, third: Float)
    // …
    }
    class WebGL(private val gl: WebGLRenderingContext) : GL {
    override fun uniform1i(uniform: Uniform, data: Int) {
    gl.uniform1i(uniform.uniformLocation, data)
    }
    override fun uniform2f(uniform: Uniform, first: Float, second: Float) {
    gl.uniform2f(uniform.uniformLocation, first, second)
    }
    override fun uniform3f(uniform: Uniform, first: Float, second: Float, third: Float) {
    gl.uniform3f(uniform.uniformLocation, first, second, third)
    }
    }
    COMMON
    KOTLIN/JS
    

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95. expect class GLContext {
    internal fun createContext(): GL
    }
    actual class GLContext {
    internal actual fun createContext(): GL {
    return LwjglGL(…)
    }
    }
    COMMON
    

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96. expect class GLContext {
    internal fun createContext(): GL
    }
    actual class GLContext {
    internal actual fun createContext(): GL {
    return LwjglGL(…)
    }
    }
    COMMON
    KOTLIN/JVM
    

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97. IN OTHER LANGUAGES, THIS CAN OFTEN BE ACCOMPLISHED BY BUILDING A SET OF
    INTERFACES IN THE COMMON CODE AND IMPLEMENTING THESE INTERFACES IN
    PLATFORM-SPECIFIC MODULES. HOWEVER, THIS APPROACH IS NOT IDEAL IN CASES
    WHEN YOU HAVE A LIBRARY ON ONE OF THE PLATFORMS THAT IMPLEMENTS THE
    FUNCTIONALITY YOU NEED, AND YOU'D LIKE TO USE THE API OF THIS LIBRARY DIRECTLY
    WITHOUT EXTRA WRAPPERS.
    

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98. IN OTHER LANGUAGES, THIS CAN OFTEN BE ACCOMPLISHED BY BUILDING A SET OF
    INTERFACES IN THE COMMON CODE AND IMPLEMENTING THESE INTERFACES IN
    PLATFORM-SPECIFIC MODULES. HOWEVER, THIS APPROACH IS NOT IDEAL IN CASES
    WHEN YOU HAVE A LIBRARY ON ONE OF THE PLATFORMS THAT IMPLEMENTS THE
    FUNCTIONALITY YOU NEED, AND YOU'D LIKE TO USE THE API OF THIS LIBRARY DIRECTLY
    WITHOUT EXTRA WRAPPERS.
    

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99. // Common
    expect class Uniform
    // JVM
    actual class Uniform(val address: Int)
    // JVM
    override fun uniform2f(uniform: Uniform, first: Float, second: Float) {
    glUniform2f(uniform.address, first, second)
    }
    COMMON
    KOTLIN/JVM
    1. Producing
    2. Consuming
    

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100. // Common
     expect class Uniform
     // JVM
     actual class Uniform(val address: Int)
     // JVM
     override fun uniform2f(uniform: Uniform, first: Float, second: Float) {
     glUniform2f(uniform.address, first, second)
     }
     COMMON
     KOTLIN/JVM
     1. Producing
     2. Consuming
     

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101. DRAWING FIRST TRIANGLE
     

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102. val vertices = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, vertices)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertPositions(),
     GL.STATIC_DRAW)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexPosition"),
     size = 3,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexPosition"))
     

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103. val vertices = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, vertices)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertPositions(),
     GL.STATIC_DRAW)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexPosition"),
     size = 3,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexPosition"))
     X Y Z
     

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104. val colors = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertColors(),
     GL.STATIC_DRAW)
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexColor"),
     size = 4,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexColor"))
     

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105. val colors = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertColors(),
     GL.STATIC_DRAW)
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexColor"),
     size = 4,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexColor"))
     Red Green Blue Alpha
     

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106. val verticesOrder = gl.createBuffer()
     gl.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, verticesOrder)
     gl.bufferData(GL.ELEMENT_ARRAY_BUFFER,
     mesh.verticesOrder.convertOrder(), GL.STATIC_DRAW)
     gl.drawElements(mesh.drawType.glType, mesh.verticesOrder.size,
     GL.UNSIGNED_SHORT, 0)
     

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107. A
     B
     C
     D
     E
     

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108. A
     B
     C
     D
     E
     

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109. val vertices = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, vertices)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertPositions(), GL.STATIC_DRAW)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexPosition"),
     size = 3,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexPosition"))
     val colors = gl.createBuffer()
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.bufferData(GL.ARRAY_BUFFER, mesh.vertices.convertColors(), GL.STATIC_DRAW)
     gl.bindBuffer(GL.ARRAY_BUFFER, colors)
     gl.vertexAttribPointer(
     index = shader.getAttrib("aVertexColor"),
     size = 4,
     type = GL.FLOAT,
     normalized = false,
     stride = 0,
     offset = 0
     )
     gl.enableVertexAttribArray(shader.getAttrib("aVertexColor"))
     val verticesOrder = gl.createBuffer()
     gl.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, verticesOrder)
     gl.bufferData(GL.ELEMENT_ARRAY_BUFFER, mesh.verticesOrder.convertOrder(), GL.STATIC_DRAW)
     gl.drawElements(mesh.drawType.glType, mesh.verticesOrder.size, GL.UNSIGNED_SHORT, 0)
     Vertices
     Colors
     Order
     

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110. attribute vec3 aVertexPosition;
     void main() {
     gl_Position = aVertexPosition;
     }
     

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111. attribute vec4 aVertexColor;
     void main() {
     gl_FragColor = aVertexColor;
     }
     

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112. Color interpolation
     

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113. Perspective Camera
     

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114. Perspective Camera

     (wide angle)
     

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115. Orthographic
     

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116. Perspective Camera

     Frustum
     

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117. Perspective Camera

     Frustum
     

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118. https://webglfundamentals.org/webgl/lessons/webgl-3d-camera.html
     

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119. https://webglfundamentals.org/webgl/lessons/webgl-3d-camera.html
     

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120. View Slide

121. 0.1253255324554
     145343224242.12
     

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122. View Slide

123. attribute vec3 aVertexPosition;
     void main() {
     gl_Position = aVertexPosition;
     }
     

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124. attribute vec4 aVertexPosition;
     uniform mat4 uModelViewMatrix;
     uniform mat4 uProjectionMatrix;
     void main() {
     gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;
     }
     

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125. attribute vec4 aVertexPosition;
     uniform mat4 uModelViewMatrix;
     uniform mat4 uProjectionMatrix;
     void main() {
     gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;
     }
     Change for every vertex
     Common for all vertices
     

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126. Try me
     

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127. PLATFORM
     DIFFERENCES
     

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128. interface Game {
     fun render(delta: Seconds)
     }
     

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129. override fun render(delta: Seconds) {
     // --- act ---
     model.rotateZ(delta * 20)
     }
     

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130. MOBILE APP

     VERSUS
     

     DESKTOP APP
     

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131. TOUCH

     VERSUS
     

     CLICK
     

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132. LEFT CONTROL

     VERSUS
     

     CONTROL
     

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133. WEB
     INPUTS
     DESKTOP
     INPUTS
     MOBILE
     INPUTS
     TARGET API
     

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134. IMPLEMENTATION
     DETAILS
     

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135. WEB JVM ANDROID
     

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136. FIXING PLATFORMS
     IMPLEMENTATION DETAILS IS HARD
     AND CAN GIVE YOU HEADACHE
     
     
     
     
     

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137. BUT ONE PLATFORM
     CAN HELP YOU TO WORK
     ON ANOTHER ONE.
     AND THAT'S COOL
     

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138. GRADLEW -T
     GRADLE BROWSER
     WEBPACK
     Reload on change Reload on change
     

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139. SPECTORJS
     

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140. SKELETON BASED
     ANIMATIONS
     

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142. View Slide

143. View Slide

144. View Slide

145. class DemoSuzanne : Game {
     private val model: Drawable = fileHandler.get("suzanne.protobuf")
     fun render(delta: Seconds) {
     model.draw()
     }
     }
     Usage
     Synchronous loading
     

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146. class DemoSuzanne : Game {
     private val model: Drawable by fileHandler.get("suzanne.protobuf")
     fun render(delta: Seconds) {
     model.draw()
     }
     }
     

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147. open class Content(val filename: String) {
     private var isLoaded: Boolean = false
     private var content: R? = null
     operator fun getValue(thisRef: Any?, property: KProperty<*>): R {
     if (isLoaded) {
     return content!!
     } else {
     throw EarlyAccessException(filename, property.name)
     }
     }
     }
     

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148. private fun asyncContent(filename: String, enc: (ByteArray) -> T): Content {
     val url = computeUrl(filename)
     val jsonFile = XMLHttpRequest()
     jsonFile.responseType = XMLHttpRequestResponseType.Companion.ARRAYBUFFER
     jsonFile.open("GET", url, true)
     val content = Content(filename)
     jsonFile.onload = { _ ->
     if (jsonFile.readyState == 4.toShort() && jsonFile.status == 200.toShort()) {
     val element = enc((jsonFile.response as ArrayBuffer).toByteArray())
     content.load(element)
     }
     }
     jsonFile.send()
     return content
     }
     

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149. class DemoSuzanne : Game {
     private val model: Drawable by fileHandler.get("suzanne.protobuf")
     fun render(delta: Seconds) {
     model.draw()
     }
     }
     Content of the wrapper

     Not the wrapper itself
     

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150. actual fun run(gameFactory: () -> Game) {
     this.game = gameFactory()
     window.requestAnimationFrame(::loading)
     }
     private fun loading(now: Double) {
     if (!fileHandler.isFullyLoaded()) {
     window.requestAnimationFrame(::loading)
     } else {
     game.create()
     game.resume()
     window.requestAnimationFrame(::render)
     }
     }
     Get all resources to load
     Start the game
     Wait for resources to be loaded
     

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151. {
     "asset": {
     "generator": "Khronos glTF Blender I/O v1.1.46",
     "version": "2.0"
     },
     "nodes": [
     {
     "name": "Light",
     "rotation": [
     0.16907575726509094,
     0.7558803558349609,
     -0.27217137813568115,
     0.570947527885437
     ]
     }
     ],
     "buffers": [
     {
     "byteLength": 26400,
     "uri": "data:application/octet-stream;base64,…"
     }
     ]
     }
     GLTF
     

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152. JVM
     JS
     ANDROID
     GLTF
     Export
     PROTOBUF
     Conversion
     kotlinx.serialization
     

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153. @Serializable
     class Mesh(
     @ProtoId(1)
     val vertices: List = emptyList(),
     @ProtoId(2)
     val verticesOrder: IntArray = intArrayOf()
     )
     @Serializable
     class Vertex(
     @ProtoId(1)
     val position: Position,
     @ProtoId(2)
     val color: Color,
     @ProtoId(3)
     val normal: Normal,
     @ProtoId(4)
     val influence: Influence
     )
     

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154. fun readProtobuf(data: ByteArray): Model {
     val deserializer = ProtoBuf(context = serialModule())
     return deserializer.load(serializer(), data)
     }
     fun writeProtobuf(model: Model): ByteArray {
     val serializer = ProtoBuf(context = serialModule())
     return serializer.dump(Model.serializer(), model)
     }
     

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155. Joint
     Relative to
     

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156. View Slide

157. View Slide

158. Reference position
     Target position
     Move transformation
     

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159. HOW TO GET 

     THE MOVE TRANSFORMATION ?
     

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160. Origin
     A
     B
     OA + AB = OB
     

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161. Origin
     A
     B
     AB = OB - OA
     Inverse
     

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162. val animationTransformation = B.globalTransformation * inverse(A.globalTransformation)
     

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163. uniform mat4 uJointTransformationMatrix[MAX_JOINTS];
     attribute vec3 aVertexPosition;
     attribute int aJointId;
     void main() {
     mat4 uJointMatrix = uJointTransformationMatrix[aJointId];
     gl_Position = uJointMatrix * vec4(aVertexPosition, 1.0);
     }
     All animation moves transformation
     Get transformation for this vertex
     Apply transformation
     

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164. Try me
     

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165. View Slide

166. View Slide

167. View Slide

168. KOOL
     

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169. SO KOTLIN
     MULTIPLATFORM?
     Try me
     

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