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2018-05-19: this repository remains here for historical reasons, continued in


Just for fun, wanted to try new flavor of Kotlin language - Kotlin/Native

Kotlin/Native is under development, but as is - in technical preview stage - can produce reasonably-sized self-contained programs for 64-bit versions of 3 major OSes - Windows/Linux/MacOS. (It also can produce binaries for embedded/mobile devices, but in this area not so ready because of performance issues. For modern desktops performance is not critical in most cases, and it is already usable.)

Lets explore how Kotlin/Native can be used for producing small self-contained GUI applications.

UI library

We need a native GUI library with C interface - Kotlin/Native currently can interop only with libraries that have plain C API. GTK and QT are too big and complex, I wanted someting relatively small, cross-platform and with native-looking widgets.

Here it is - libui


Assume we have Windows 7 64-bit, working environment is c:\src.

Download and build Kotlin/Native :

cd \src
git clone
chdir kotlin-native
gradlew dependencies:update
gradlew dist
chdir ..

Working directory:

mkdir kotlin-ui
chdir kotlin-ui

Now we have two sibling directories: \src\kotlin-native and \src\kotlin-ui.

Low-Level bindings

Create and enter working directory:

mkdir libui
chdir libui

Download and unpack libui tarball:

wget --no-check-certificate  -O libui.tgz`
7z x libui.tgz -so | 7z x -si -ttar

(or use your favorite programs to download and unpack)

Create libui\libui.def:

headers = ui.h
headerFilter = ui.h
compilerOpts = -I./alpha3.1/src

Create and run libui\build.bat:

@echo off
set KOTLIN_HOME=..\..\kotlin-native\dist
call cinterop -def libui.def -o libui || exit /b
rename libui-build build-native

It should produce libui.klib - native bindings for Kotlin/Native :)

High-Level bindings

Now we have direct binding for libui, but it is too low-level for user code.

Lets create one more level to isolate this low-level API - uiWidgets.kt

(TODO: complete bindings, something like TornadoFX)

Test program

Create simple test:

fun main(args: Array<String>) = ui.application {
    val window = ui.Window("Button example", width=320, height=60)
    window.margined = true

    val button = ui.Button()
    button.text = "Konan ãîâîðèò: click me!"
    button.onClick { println ("Hi Kotlin") }
    window.child = button

Create and run build.bat:

@echo off
set "PATH=..\kotlin-native\dist\bin;%PATH%"
set LFLAGS=libui\alpha3.1\windows_amd64\mingw_static\libui.a^
        -luser32 -lkernel32 -lusp10 -lgdi32 -lcomctl32 -luxtheme^
        -lmsimg32 -lcomdlg32 -ld2d1 -ldwrite -lole32 -loleaut32^
        -loleacc -luuid -mwindows
call konanc src libui/kotlin -library libui/libui -linkerOpts "%LFLAGS%" -o test

Result - test.exe - when runned should draw small window with one button inside.


OK, but how to debug?

Currently Kotlin/Native have very limited debugging capabilites. Sure it will improve someday, but what to do now?

There is a way. Kotlin/Native itself is JVM program, written in Kotlin/JVM . But it also heavily use LLVM toolchain, and LLVM is native. How these two parts interact? And how compiler developers debug it?

Looking in Kotlin/Native sources, one can find JVM version of Interop . It is almost similar to native cinterop, but designed to work with "big" Kotlin, using under the hood sun.misc.Unsafe and ffi.

But this way anyone can develop and debug in familiar and powerful IDEA, and then just compile to native!

Lets try.

First, quick and dirty, just copy jvm-citerop to our working directory:

xcopy /E /I \src\kotlin-native\Interop\Runtime\src\jvm cinterop\jvm\
xcopy /E /I \src\kotlin-native\Interop\Runtime\src\main cinterop\main\
xcopy /E /I \src\kotlin-native\dist\konan\nativelib\callbacks.dll cinterop

Now, we need to generate jvm bindings for libui.

Modify libui\libui.def like this:

headers = ui.h
headerFilter = ui.h

compilerOpts = -I./alpha3.1/src -std=c99 -fPIC \
    -Wall -W -Wno-unused-parameter -Wwrite-strings -Wmissing-field-initializers \
    -pedantic -Wno-long-long -Wcovered-switch-default -Wdelete-non-virtual-dtor \

linker = clang++

linkerOpts = -fPIC -fvisibility-inlines-hidden \
    -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers \
    -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -Wdelete-non-virtual-dtor \
    -std=c++11 \

And libui\build.bat:

@echo off

set KOTLIN_HOME=..\..\kotlin-native\dist

set LFLAGS=alpha3.1\windows_amd64\mingw_static\libui.a^
        -luser32 -lkernel32 -lusp10 -lgdi32 -lcomctl32 -luxtheme^
        -lmsimg32 -lcomdlg32 -ld2d1 -ldwrite -lole32 -loleaut32^
        -loleacc -luuid^
        -static-libgcc -static-libstdc++^
        -Wl,-Bstatic,--whole-archive -lwinpthread -Wl,--no-whole-archive,-Bdynamic

call cinterop -def libui.def -flavor jvm -linkerOpts "%LFLAGS%" -o libui
rename libui-build build-jvm

call cinterop -def libui.def -o libui || exit /b
rename libui-build build-native

This "magic" was mostly copied from kotlin-native\backend.native\llvm.def

But citerop don't like undocumented -flavor option, so I just patched kotlin sources, and rebuild. Yes, quick and dirty :)

@@ -329,11 +329,11 @@ private fun processLib(konanHome: String,
                        args: Map<String, List<String>>) {

     val userDir = System.getProperty("user.dir")
     val ktGenRoot = args["-generated"]?.single() ?: userDir
     val nativeLibsDir = args["-natives"]?.single() ?: userDir
-    val flavorName = args["-flavor"]?.single() ?: "jvm"
+    val flavorName = args["-flavor"]?.lastOrNull() ?: "jvm"
     val flavor = KotlinPlatform.values().single {, ignoreCase = true) }
     val target = args["-target"]?.single()?.targetSuffix() ?: defaultTarget
     val defFile = args["-def"]?.single()?.let { File(it) }
     val manifestAddend = args["-manifest"]?.single()?.let { File(it) }

Now, running libui\build.bat should produce both native and jvm bindings.

And finally, create IDEA kotlin project in our working directory, add source paths (Ctrl+Alt+Shift+S) - libui/kotlin, build-jvm/kotlin, cinterop add native paths libui/build-jvm/natives and cinterop

Trying to run - we get error, something like "ffi not loaded". OK, patch our copy of cinterop, quick and dirty again:

--- "F:\src\kotlin-native\Interop\Runtime\src\jvm\kotlin\kotlinx\cinterop\JvmCallbacks.kt"
+++ "F:\src\kotlin-ui\cinterop\jvm\JvmCallbacks.kt"
@@ -201,7 +201,6 @@
     val kFunction = function as? KFunction<*> ?: function.reflect() ?:
             throw IllegalArgumentException(errorMessage)

+    loadCallbacksLibrary()
     val returnType = getArgOrRetValCType(kFunction.returnType)
     val paramTypes = { getArgOrRetValCType(it.type) }

Finally it should work, you can develop and debug in IDEA.

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