Curious question about Skiko implementation: Why the JNI implementation is written in C++ and not ex...

# compose-desktop

[SrSouza]

Curious question about Skiko implementation: Why the JNI implementation is written in C++ and not exposed by Kotlin Native? I saw couple examples using KN for JNI.
I'm looking to understand that because I'm starting a library multiplatform that will require JNI for JVM.

[gildor]

Why the JNI implementation is written in C++ and not exposed by Kotlin Native

There is no interopability between K/N and JVM, so it still require JNI (or similar mechanisms) as with any other native API

[gildor]

It was requested, to have an interop between K/N and JVM but there are no short plans for this

[SrSouza]

I mean something like this:

@CName("Java_org_jonnyzzz_jni_java_NativeHost_callInt")
fun callInt(env: CPointer<JNIEnvVar>, clazz: jclass, it: jint): jint {
  initRuntimeIfNeeded()
  Platform.isMemoryLeakCheckerActive = false

  println("Native function is executed with: $it")
  return it + 1
}

From: https://jonnyzzz.com/blog/2019/12/15/jni-kotlin/

Hopefully in short future we have KN/JVM interop because would be a big plus for native libraries, specially desktop ones that most of the code is Native libraries

[gildor]

Hopefully in short future

I’m very doubt about this.
Though I would love to see such feature

[gildor]

I mean something like this:

This is not a JNI per se, this is essentially exposing K/N API as C API

[Albert Chang]

Skia is an external library which is written in C++. What's the point of using K/N given that it adds K/N-C++ interop?

[gildor]

I really doubt about direct C++ interop

[gildor]

but it’s easy to expose C++ API as C API which is what many C libraries are doing and K/N already can work with C and expose own API as C API

[gildor]

so if K/N would provide some inerop tool for JVM, it could just generate JNI for easy interop between K/N and K/JVM

[gildor]

Now to interop between K/N and K/JVM you have to write JNI manually or use tool which does this for you

[Albert Chang]

Yeah that's the case when the native part is also written in K/N. However skia is written in C++ so calling C++ in K/N (or creating C API for the whole library) doesn't seem a good choice.

[gildor]

Yep, you right

[gildor]

But K/N anyway need interop with Skia, so you anyway need C to work with it

[gildor]

Also I believe there is experimental C API in Skia

[gildor]

But even withotu C API, you can write C++ code which wraps C++ API and exposes own C API for parts which you need

[SrSouza]

Skiko in KN was access to Skia, evev if they use C++ to expose C to KN (I don't know if this is the case) they also have JNi binding, só you have both, this is what I struggling here. Why do both what are the benefits or the issues with using KN for JNI as well

[gildor]

JNI binding is used by K/JVM to work with Skia

[gildor]

Skiko is MP library, it provides implementation not only for native but also for JVM