Zero-overhead, type-safe native interop with Kotlin

kotlin_native_interop.kt

// WARNING: This is not valid Kotlin code. The typealias keyword
// has not been implemented yet and may not work as shown below.

// This is like a C typedef. You can pass a GLint/GLenum where an
// Int is expected, but you cannot do the opposite, would be a
// compile-time error.
typealias GLint = Int
typealias GLenum = Int

// Native pointer values are usually mapped to Java longs. We can
// get fancy here with type parameters (e.g. Pointer<Foo>) or be
// more specific (e.g. UINT32Pointer), but lets just treat this as
// an opaque pointer to an arbitrary native data structure.
typealias Pointer = Long

// Lets use GLsync from the ARB_sync OpenGL extension. This is an
// alias to an alias, so GLsync is still a primitive long.
typealias GLsync = Pointer

// We cannot assign Long to Pointer, so a cast is necessary.
public val NULL: Pointer = 0L as Pointer

// The following definitions would be auto-generated by LWJGL.
public val GL_SYNC_GPU_COMMANDS_COMPLETE: GLenum = 0x9117 as GLenum

public val GL_OBJECT_TYPE: GLenum = 0x9112 as GLenum
public val GL_SYNC_CONDITION: GLenum = 0x9113 as GLenum
public val GL_SYNC_STATUS: GLenum = 0x9114 as GLenum
public val GL_SYNC_FLAGS: GLenum = 0x9115 as GLenum

public val GL_UNSIGNALED: GLint = 0x9118 as GLint
public val GL_SIGNALED : GLint = 0x9119 as GLint

// virtual constructor
public fun GLsync(condition: GLenum, flags: Int): GLsync =
	GL32.glFenceSync(condition, flags) as GLsync // glFenceSync returns a long, cast to GLsync

// extension function on the typealias
public fun GLsync.get(pname: GLenum): GLint =
	GL32.glGetSynci(this, pname, NULL) as GLint

fun test() {
    // We cannot pass simple ints to GLenum parameters.
    // Also, auto-complete suggests GLenums only.
    val sync = GLsync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0)
    glFinish()
    // sync is just a long in bytecode, but in Kotlin
    // we can use all kinds of goodies.
    assertTrue(sync[GL_SYNC_STATUS], GL_SIGNALED)
}

// Structs are interesting too:

typealias BytePointer = Pointer // char*

// sun.misc.Unsafe stuff
fun BytePointer.get(offset: Int): Byte = memGetByte(this + offset)
fun BytePointer.set(offset: Int, value: Byte): Unit = memPutByte(this + offset, value)

// Generated
typealias GLFWimage = Pointer

var GLFWimage.width: Int
	get() = memGetInt(this + 0)
	set(width: Int) = memPutInt(this + 0, width)

var GLFWimage.height: Int
	get() = memGetInt(this + 4)
	set(height: Int) = memPutInt(this + 4, height)

val GLFWimage.pixels: BytePointer
	get() = memGetAddress(8) as BytePointer

fun testStructs() {
	val img: GLFWimage = ...
	img.width = 32
	img.height = 32
	for ( y in 0..31 ) {
		for (  x in 0..31 ) {
			img.pixels[y * 32 + x] = 127
		}
	}
}