huanglizhuo / skiko

Kotlin MPP bindings to Skia

Kotlin Multiplatform bindings to Skia

Skiko (short for Skia for Kotlin) is the graphical library exposing significant part of Skia library APIs to Kotlin, along with the gluing code for rendering context. At the moment, Linux(x86_64), Windows(x86_64) and macOS(x86_64) builds for Kotlin/JVM are available. Using the library from Kotlin is as simple as:

fun main(args: Array<String>) {
    SkiaWindow().apply {
        layer.renderer = Renderer { renderer, w, h ->
            val canvas = renderer.canvas!!
            val paint1 = Paint().setColor(0xffff0000.toInt()) // ARGB
            canvas.drawRRect(RRect.makeLTRB(10f, 10f, w - 10f, h - 10f, 5f), paint1)
            val paint2 = Paint().setColor(0xff00ff00.toInt()) // ARGB
            canvas.drawRRect(RRect.makeLTRB(30f, 30f, w - 30f, h - 30f, 10f), paint2)

        }
        setVisible(true)
        setSize(800, 600)
    }
}

class Renderer(val displayScene: (Renderer, Int, Int) -> Unit): SkiaRenderer {
    val paint = Paint().apply {
            setColor(0xff9BC730L.toInt())
            setMode(PaintMode.FILL)
            setStrokeWidth(1f)
    }

    var canvas: Canvas? = null

    override fun onInit() {
    }

    override fun onDispose() {
    }

    override fun onReshape(width: Int, height: Int) {
    }

    override fun onRender(canvas: Canvas, width: Int, height: Int) {
        this.canvas = canvas
        displayScene(this, width, height)
    }
}

With the following build.gradle:

plugins {
    id 'org.jetbrains.kotlin.jvm' version '1.3.72'
    id 'application'
}

repositories {
    mavenLocal()
    jcenter()
    maven {
       url 'https://packages.jetbrains.team/maven/p/ui/dev'
    }
}

def os = System.getProperty("os.name")
def target = ""
if (os == "Mac OS X") {
    target = "macos"
} else if (os.startsWith("Win")) {
    target = "windows"
} else if (os.startsWith("Linux")) {
    target = "linux"
} else {
    throw Error("Unsupported OS: $target")
}

dependencies {
    implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
    implementation "org.jetbrains.skiko:skiko-jvm-runtime-$target:0.1.5"
}

application {
    mainClassName = 'AppKt'
}

Building JVM bindings

• (Optional) Set SKIA_DIR to location of Skia (binaries can be downloaded here)
• Set JAVA_HOME to location of JDK, at least version 11
• cd skiko && ./gradlew publishToMavenLocal will build the artefact and publish it to local Maven repo

Working with Skia or Skija sources

Gradle build downloads the necessary version of Skia & Skija by default. However, if downloaded sources are modified, changes are discarded (Gradle re-evaluates tasks, when outputs are changed). To use custom version of the dependencies, specify SKIA_DIR or SKIJA_DIR environment variable respectively.

Building on Windows

Using Visual Studio C++

• Install Visual Studio Build Tools or Visual Studio C++.
• If Gradle fails to find Visual C++ toolchain:

Execution failed for task ':compileDebugWindowsCpp'.
> No tool chain is available to build C++ for host operating system 'Windows 10' architecture 'x86-64':
    - Tool chain 'visualCpp' (Visual Studio):
        - Could not locate a Visual Studio installation, using the command line tool, Windows registry or system path.

set SKIKO_VSBT_PATH environment variable to the location of installed Visual Studio Build Tools. This could be done in the UI:

Control Panel|All Control Panel Items|System|Advanced system settings|Environment variables

or by running cmd as administrator:

setx /M SKIKO_VSBT_PATH "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools"