search

kool-engine / kool

An OpenGL / WebGPU engine for Desktop JVM, Android and Javascript written in Kotlin
https://fabmax.github.io/kool/kool-js
Apache License 2.0
306 stars 20 forks source link
3d android deferred-shading game-development kotlin kotlin-multiplatform opengl pbr-shading physics vulkan webgl2 webgpu

readme

kool - An OpenGL / WebGPU graphics engine written in Kotlin

License Maven Central Build

A multi-platform OpenGL / WebGPU / Vulkan game engine that works on Desktop Java, Android and browsers.

Get In Touch

Feel free to join the Discord Server!

Scene Editor

Check out the web editor! (Chrome recommended).

The engine used to be a code-only engine, but I recently made some progress in implementing a graphical scene editor. The editor still is in an early state and lacks several rather essential features, but the basics already work quite well. It is fully implemented within the engine itself (including the UI).

To unleash the full potential of the editor, you should run it locally. You can either download the editor directly in the web-version by clicking the Save Project button in the upper right corner (this also preserves any changes made in the editor) or you can clone the editor template project (see usage below).

More editor related documentation is available in the editor docs.

Web-Demos

The following demos run directly in the browser. Chrome is recommended but other browsers might work as well. All demos are implemented in code-only fashion (i.e. without using the editor). The code for all demos is available in the kool-demo subproject.

By default, the web demos use the WebGPU backend and fall back to WebGL if WebGPU is not supported by your browser. The used backend is printed in the extended info-panel in the lower right corner (click on the little +), apart from that there shouldn't be much visible difference in the WebGL and WebGPU backends. You can also force a certain backend by appending &backend=webgpu or &backend=webgl to the URL.

I also made an actual game with this: Blocks and Belts. Give it a try (it's free)!

Platform Support

Platform Backend Implementation Status
Desktop JVM OpenGL :white_check_mark: Fully working
Desktop JVM Vulkan :x: Not working (under construction)
Browser WebGL 2 :white_check_mark: Fully working
Browser WebGPU :white_check_mark: Fully working
Android OpenGL ES 3 :sparkles: kool-core fully working (but no physics yet)

Android Support

The Android target is disabled by default (to avoid having the Android SDK as a build requirement). You can enable the Android target by running the gradle task enableAndroidPlatform.

Moreover, Android support is only available for kool-core for now. Therefore, the demos don't work on Android yet (because they also require kool-physics). However, there's a basic kool-android-template project with a minimal kool Android app.

Usage

If you are adventurous, you can use kool as a library in your own (multiplatform-) projects. The library is published on maven central, and there is a separate repo containing a minimal template project to get you started:

https://github.com/kool-engine/kool-templates

The demos mentioned above and examples shown below should give you a rough idea on how to do stuff (documentation is still a bit of a weak spot).

Running the Demos on JVM

You can launch the desktop demo app directly from a terminal via gradle with ./gradlew :kool-demo:run.

Running the main() method from within IntelliJ requires that the native libraries are located in a local folder and added as file dependencies (seems to be some kind of dependency resolution bug in IntelliJ when importing multiplatform projects with JVM runtimeOnly libraries).

The required libs are copied automatically on build. So, in order to launch the demos from within IntelliJ you need to build the project first (or manually run the cacheRuntimeLibs task) and then re-sync the gradle project, so that the libs are resolved and added to the IntelliJ module classpath.

Engine Features / Noticeable Stuff:

A Hello World Example

Getting a basic scene on the screen is quite simple:

fun main() = KoolApplication {
    addScene {
        defaultOrbitCamera()

        addColorMesh {
            generate {
                cube {
                    colored()
                }
            }
            shader = KslPbrShader {
                color { vertexColor() }
                metallic(0f)
                roughness(0.25f)
            }
            onUpdate {
                transform.rotate(45f.deg * Time.deltaT, Vec3f.X_AXIS)
            }
        }

        lighting.singleDirectionalLight {
            setup(Vec3f(-1f, -1f, -1f))
            setColor(Color.WHITE, 5f)
        }
    }
}

The above example creates an application with a single scene and sets up a mouse-controlled camera (with defaultOrbitCamera()). As you might have guessed the addColorMesh { ... } block creates a colored cube and adds it to the scene. In order to draw the mesh on the screen it needs a shader, which is assigned with shader = KslPbrShader { ... }. This creates a simple PBR shader for a dielectric material with a rather smooth surface. Color information is taken from the corresponding vertex attribute. The onUpdate-block is called on each frame and modifies the cube transform to rotate it 45° per second around its X-axis. Finally, we set up a single directional scene light (of white color and an intensity of 5), so that our cube can shine in its full glory. The resulting scene looks like this.

Model Loading and Advanced Lighting

Model loading, animation and more advanced lighting with shadow mapping and ambient occlusion requires only a few more lines of code:

fun main() = KoolApplication {
    addScene {
        defaultOrbitCamera()

        // Light setup
        lighting.singleSpotLight {
            setup(Vec3f(5f, 6.25f, 7.5f), Vec3f(-1f, -1.25f, -1.5f), 45f.deg)
            setColor(Color.WHITE, 300f)
        }
        val shadowMap = SimpleShadowMap(this, lighting.lights[0])
        val aoPipeline = AoPipeline.createForward(this)

        // Add a ground plane
        addColorMesh {
            generate {
                grid { }
            }
            shader = KslPbrShader {
                color { constColor(Color.WHITE) }
                shadow { addShadowMap(shadowMap) }
                enableSsao(aoPipeline.aoMap)
            }
        }

        // Load a glTF 2.0 model
        launchOnMainThread {
            val materialCfg = GltfFile.ModelMaterialConfig(
                shadowMaps = listOf(shadowMap),
                scrSpcAmbientOcclusionMap = aoPipeline.aoMap
            )
            val modelCfg = GltfFile.ModelGenerateConfig(materialConfig = materialCfg)
            val model = Assets.loadGltfModel("path/to/model.glb", modelCfg)

            model.transform.translate(0f, 0.5f, 0f)
            if (model.animations.isNotEmpty()) {
                model.enableAnimation(0)
                model.onUpdate {
                    model.applyAnimation(Time.deltaT)
                }
            }

            // Add loaded model to scene
            addNode(model)
        }
    }
}

First we set up the lighting. This is very similar to the previous example but this time we use a spot-light, which requires a position, direction and opening angle. Other than directional lights, point and spot-lights have a distinct (point-) position and objects are affected less by them, the farther they are away. This usually results in a much higher required light intensity: Here we use an intensity of 300.

Next we create a SimpleShadowMap which computes the shadows cast by the light source we defined before. Moreover, the created AoPipeline computes an ambient occlusion map, which is later used by the shaders to further improve the visual appearance of the scene.

After light setup we can add objects to our scene. First we generate a grid mesh as ground plane. Default size and position of the generated grid are fine, therefore grid { } does not need any more configuration. Similar to the color cube from the previous example, the ground plane uses a PBR shader. However, this time we tell the shader to use the ambient occlusion and shadow maps we created before. Moreover, the shader should not use the vertex color attribute, but a simple pre-defined color (white in this case).

Finally, we want to load a glTF 2.0 model. Resources are loaded via the Assets object. Since resource loading is a potentially long-running operation we do that from within a coroutine launched with launchOnMainThread { ... }. By default, the built-in glTF parser creates shaders for all models it loads. The created shaders can be customized via a provided material configuration, which we use to pass the shadow and ambient occlusion maps we created during light setup. After we created the custom model / material configuration we can load the model with Assets.loadGltfModel("path/to/model.glb", modelCfg). This suspending function returns the loaded model, which can then be customized and inserted into the scene. Here we move the model 0.5 units along the y-axis (up). If the model contains any animations, these can be easily activated. This example checks whether there are any animations and if so activates the first one. The model.onUpdate { } block is executed on every frame and updates the enabled animation. The model is inserted into the scene with addNode(model). Calling addNode(model) from within the coroutine is fine, since the coroutine is launched via launchOnMainThread { ... } and therefor is executed by the main render thread. If a different coroutine context / thread were used, we had to be careful to not modify the scene content while it is rendered.

The resulting scene looks like this. Here, the Animated Box from the glTF sample repository is loaded.

Kool UI

Kool comes with an embedded UI framework, which is heavily inspired by Jetpack Compose but was implemented from scratch. Here is a small example:

fun main() = KoolApplication {
    addScene {
        setupUiScene(Scene.DEFAULT_CLEAR_COLOR)

        addPanelSurface(colors = Colors.singleColorLight(MdColor.LIGHT_GREEN)) {
            modifier
                .size(400.dp, 300.dp)
                .align(AlignmentX.Center, AlignmentY.Center)
                .background(RoundRectBackground(colors.background, 16.dp))

            var clickCount by remember(0)
            Button("Click me!") {
                modifier
                    .alignX(AlignmentX.Center)
                    .margin(sizes.largeGap * 4f)
                    .padding(horizontal = sizes.largeGap, vertical = sizes.gap)
                    .font(sizes.largeText)
                    .onClick { clickCount++ }
            }
            Text("Button clicked $clickCount times") {
                modifier
                    .alignX(AlignmentX.Center)
            }
        }
    }
}

Here, we create a new Scene and configure it to be a UI scene containing a single panel surface. Within the addPanelSurface-block, we add a button and a text field. All appearance and layout-properties of the UI elements are controlled by their modifiers.

Whenever the button is clicked we increment a clickCount which is then displayed by the text field. This works because the addPanelSurfcae-block is executed each time any remembered state (or mutableStateOf()) within the block changes.

The resulting scene looks like this.

More complex layouts can be created by nesting Row { } and Column { } objects. The kool editor as well as the full UI demo should give you an impression on what's possible.

Kool Shader Language

Kool comes with its own shader language (called ksl), which is implemented as a Kotlin Type-safe builder / DSL. The ksl shader code you write is used to generate the actual GLSL / WGSL shader code. The benefit with this approach is that there is no hard-coded platform-specific shader code in common code and all shaders work on OpenGL / GLSL as well as WebGPU / WGSL. Moreover, it is relatively easy to add different generators which generate shader code for different backends in the future (e.g. metal).

Writing shaders in ksl is quite similar to GLSL, here's how a hello-world style shader looks like:

fun main() = KoolApplication {
    addScene {
        defaultOrbitCamera()

        addColorMesh {
            generate {
                cube {
                    colored()
                }
            }
            shader = KslShader("Hello world shader") {
                val interStageColor = interStageFloat4()
                vertexStage {
                    main {
                        val mvp = mvpMatrix()
                        val localPosition = float3Var(vertexAttribFloat3(Attribute.POSITIONS))
                        outPosition set mvp.matrix * float4Value(localPosition, 1f.const)
                        interStageColor.input set vertexAttribFloat4(Attribute.COLORS)
                    }
                }
                fragmentStage {
                    main {
                        colorOutput(interStageColor.output)
                    }
                }
            }
        }
    }
}

The interesting part starts at shader = KslShader() = { ... }. Here a new shader is created and assigned to the mesh created before. If you ever wrote a shader before the structure should be familiar: The shader consists of a vertex stage (responsible for projecting the individual mesh vertices onto the screen) and a fragment stage (responsible for computing the output-color for each pixel covered by the mesh). This example shader is almost as simple as a valid shader can be: It uses a pre-multiplied MVP matrix to project the vertex position attribute to the screen. Moreover, the color attribute is taken from the vertex input and forwarded to the fragment shader via interStageColor. The fragment stage then simply takes the color from interStageColor and writes it to the screen.

A little more complex example is available in HelloKsl, which looks like this. Of course, shaders can get more complex than that, you can dig further into the code. All shaders currently used in kool are written in ksl.

Physics Simulation

After playing around with various different engines on javascript and JVM I came to the conclusion that all of them had some kind of flaw. So I decided to write my own bindings for Nvidia PhysX: physx-jni for JVM, and physx-js-webidl for javascript.

This was quite a bit of work, but I think it was worth it: By writing my own bindings I get the features I need, and, even better, I get the same features for javascript and JVM, which makes the multiplatform approach much easier.