Getting Started – Kotlin SDK

Alpha – GoudEngine is under active development. APIs change frequently. Report issues

This guide covers installing the Kotlin SDK, opening a window, drawing a sprite, and handling input.

See also: C# guide – Python guide – TypeScript guide – Rust guide – Swift guide – Go guide

Prerequisites

JDK 17 or later (Temurin recommended)
Gradle 8.5+ (wrapper included in the SDK)
Rust toolchain – needed to build the native engine library

Building the Native Library

The Kotlin SDK wraps the native Rust engine through JNI. Build the engine first:

git clone https://github.com/aram-devdocs/GoudEngine.git
cd GoudEngine
cargo build --release -p goud-engine-core

This produces the native library that the Kotlin JNI layer loads at runtime.

Installation

Gradle (from source)

Add the SDK as a local dependency. In your build.gradle.kts:

dependencies {
    implementation(files("path/to/sdks/kotlin/build/libs/goudengine-0.0.832.jar"))
}

Maven Central (when published)

dependencies {
    implementation("io.github.aram-devdocs:goudengine:0.0.833")
}

Build the SDK jar

cd sdks/kotlin
./gradlew build --no-daemon

The Gradle build task automatically compiles the native Rust library and bundles it into the jar under native/.

First Project

Create a Kotlin file with a minimal window that closes on Escape:

import com.goudengine.core.EngineConfig
import com.goudengine.core.GoudEngine
import com.goudengine.core.GoudGame

fun main() {
    GoudEngine.ensureLoaded()

    val game = EngineConfig.create()
        .title("My First Game")
        .width(800)
        .height(600)
        .build()

    while (!game.shouldClose()) {
        game.beginFrame()
        // draw here
        game.endFrame()
    }

    game.destroy()
}

Build and run:

./gradlew run

A window opens at 800x600 and closes when you press Escape.

beginFrame clears the screen and prepares the frame. endFrame swaps buffers and polls events. Everything you draw goes between those two calls.

Drawing a Sprite

Load textures once before the loop. Drawing happens between beginFrame and endFrame.

import com.goudengine.core.EngineConfig
import com.goudengine.core.GoudEngine
import com.goudengine.types.Color

fun main() {
    GoudEngine.ensureLoaded()

    val game = EngineConfig.create()
        .title("Sprite Demo")
        .width(800)
        .height(600)
        .build()

    val texture = game.loadTexture("assets/player.png")

    while (!game.shouldClose()) {
        game.beginFrame()

        game.drawSprite(texture, 400f, 300f, 64f, 64f, 0f, Color.white())

        game.endFrame()
    }

    game.destroy()
}

Put your image files in an assets/ folder next to your project. The path is relative to the working directory.

Handling Input

isKeyJustPressed returns true only on the frame the key goes down. Use isKeyPressed for held-down detection.

import com.goudengine.input.Key
import com.goudengine.input.MouseButton

// One-shot: true only on the frame the key goes down
if (game.isKeyJustPressed(Key.Space.value)) {
    // jump
}

// Held: true every frame the key is down
if (game.isKeyPressed(Key.W.value)) {
    y -= speed * game.deltaTime
}
if (game.isKeyPressed(Key.S.value)) {
    y += speed * game.deltaTime
}

// Mouse
if (game.isMouseButtonPressed(MouseButton.Left.value)) {
    val pos = game.getMousePosition()
    // use pos.x, pos.y
}

deltaTime is the elapsed seconds since the last frame. Use it to make movement frame-rate independent.

Value Types

The SDK provides Kotlin data classes for common types:

import com.goudengine.types.Vec2
import com.goudengine.types.Vec3
import com.goudengine.types.Color
import com.goudengine.types.Rect

val position = Vec2(100f, 200f)
val direction = position.normalize()
val distance = position.distance(Vec2.zero())

val color = Color.rgb(1f, 0f, 0f) // red
val transparent = color.withAlpha(0.5f)

val bounds = Rect(0f, 0f, 100f, 50f)
val inside = bounds.contains(Vec2(50f, 25f)) // true

Running an Example Game

The repository includes a complete Flappy Bird clone in Kotlin:

git clone https://github.com/aram-devdocs/GoudEngine.git
cd GoudEngine
cargo build --release
./dev.sh --sdk kotlin --game flappy_bird

Source is in examples/kotlin/flappy_bird/.

API Documentation

Generate HTML docs with Dokka:

cd sdks/kotlin
./gradlew dokkaHtml --no-daemon
# output in build/dokka/html/

All Java/Kotlin source files under src/main/java/com/goudengine/internal/ and the Kotlin wrapper classes are auto-generated by codegen/gen_kotlin.py. Do not hand-edit generated files. Regenerate with:

python3 codegen/gen_kotlin.py

Next Steps

Kotlin SDK docs – SDK-specific documentation
Kotlin examples source – complete game source code
Build Your First Game – end-to-end minimal game walkthrough
Example Showcase – current cross-language parity matrix
SDK-first architecture – how the engine layers fit together
Development guide – building from source, version management, git hooks
Other getting started guides: C# – Python – TypeScript – Rust – Swift – Go – Lua

GoudEngine Documentation