B4J Code Snippet Native Linker (Java 19+ Only)

I have been trying out the replacement for JNA in Java 19.
The code needed to call a library function is far cleaner now, and requires less coding.

The following in-line java calls strlen from stdlib and prints the length of the string. (Not exciting code but shows how little you need to write now).
Just a taster for now.

#Region Project Attributes
    #MainFormWidth: 600
    #MainFormHeight: 600
    ' ### needed for java 19 ###
    #VirtualMachineArgs: --enable-preview --enable-native-access=ALL-UNNAMED
    #PackagerProperty: VMArgs = --enable-preview
    ' ##########################
#End Region
' the usual app here that calls the inline java
...
#if java
import java.lang.foreign.*;
import java.lang.invoke.*;

public static void doIt() throws Throwable {
    // 1. Get a lookup object for commonly used libraries
    SymbolLookup stdlib = Linker.nativeLinker().defaultLookup();

    // 2. Get handle to the "strlen" function in the C standard library
    MethodHandle strlen = Linker.nativeLinker().downcallHandle(
        stdlib.lookup("strlen").orElseThrow(),
        FunctionDescriptor.of(ValueLayout.OfLong.JAVA_LONG, ValueLayout.OfAddress.ADDRESS));

    // 3. Convert Java String to C string and store it in off-heap memory
    MemorySegment str = SegmentAllocator.implicitAllocator().allocateUtf8String("B4X for coding!");

    // 4. Invoke the foreign function
    long len = (long) strlen.invoke(str);

    System.out.println("len = " + len);
  }

#End If

Looking forward to more experiments.

Note: It will not run in the IDE ( I had to modify some arguments that get passed to javac in order to compile the preview code).

ps. Sorry Erel if this is in the wrong part of the forum.

 

[Daestrum]

So after some more tries I managed to re-write the Joypad code I wrote a few years back.

It seems shorter to me, and will work from in-line java, don't think I ever got the JNA version to work, that's why I made the library.

The following code doesn't use all the buttons/triggers of the pad, but that can easily be added (by you) if you want to use it.

Note: again this won't run for you in the IDE.

#Region Project Attributes 
    #MainFormWidth: 600
    #MainFormHeight: 600 
    ' ### needed for java 19 ###
    #VirtualMachineArgs: --enable-preview --enable-native-access=ALL-UNNAMED
    #PackagerProperty: VMArgs = --enable-preview
    ' ##########################    
#End Region

Sub Process_Globals
    Private fx As JFX
    Private MainForm As Form
    Private xui As XUI 
    Private Button1 As B4XView
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.RootPane.LoadLayout("Layout1")
    MainForm.Show
End Sub

Sub Button1_Click
    'xui.MsgboxAsync("Hello World!", "B4X")
    (Me).As(JavaObject).RunMethod("doIt",Null)
End Sub
#if java
import java.lang.foreign.*;
import java.lang.invoke.*;
import java.lang.foreign.ValueLayout.*;

    // define the structure XINPUT_STATE    
    static GroupLayout XINPUT_STATE = MemoryLayout.structLayout(OfInt.JAVA_INT.withName("dwPacketNumber"),
            OfShort.JAVA_SHORT.withName("wButtons"), OfByte.JAVA_BYTE.withName("bLeftTrigger"),
            OfByte.JAVA_BYTE.withName("bRightTrigger"), OfShort.JAVA_SHORT.withName("sThumbLX"),
            OfShort.JAVA_SHORT.withName("sThumbLY"), OfShort.JAVA_SHORT.withName("sThumbRX"),
            OfShort.JAVA_SHORT.withName("sThumbRY")).withName("IState");
    
    // define structure ena
    static GroupLayout ena = MemoryLayout.structLayout(ValueLayout.OfBoolean.JAVA_BOOLEAN.withName("enabled"));
    
    // define the variables we will access in the structures
    static VarHandle buttons = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("wButtons"));
    static VarHandle LTrig = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("bLeftTrigger"));
    static VarHandle RTrig = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("bRightTrigger"));
    static VarHandle LThumbX = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("sThumbLX"));
    static VarHandle LThumbY = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("sThumbLY"));
    static VarHandle RThumbX = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("sThumbRX"));
    static VarHandle RThumbY = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("sThumbRY"));

    static VarHandle PackNo = XINPUT_STATE.varHandle(MemoryLayout.PathElement.groupElement("dwPacketNumber"));

    static VarHandle enabledFlag = ena.varHandle(MemoryLayout.PathElement.groupElement("enabled"));

    public static void doIt() {
        try {
            // set up memorySession - can be inside or outside the JVM
            var memorySession = MemorySession.openConfined();
            
            // allocate so memory for the structure
            var xin = memorySession.allocate(XINPUT_STATE);

            // set up linkers & loaders
            Linker nativeLinker = Linker.nativeLinker();
            SymbolLookup stdlibLookup = nativeLinker.defaultLookup();
            SymbolLookup loaderLookup = SymbolLookup.loaderLookup();
            
            // load System library XInput1_4
            System.loadLibrary("XInput1_4");
            
            //get method XInputEnable in XInput1_4.dll
            MethodHandle enable = nativeLinker.downcallHandle(
                    stdlibLookup.lookup("XInputEnable").or(() -> loaderLookup.lookup("XInputEnable")).orElseThrow(),
                    FunctionDescriptor.of(OfInt.JAVA_INT,OfAddress.ADDRESS /*OfBoolean.JAVA_BOOLEAN*/));

            //Enable readings on joystick/gamepad
            // allocate some memory and invoke foreign function
            var enab = memorySession.allocate(ena);
            // format is VarHandleName .set (memorySessionName , theValueYouWantToSet)
            enabledFlag.set(enab, true);
            enable.invoke(enab);
            //just a check
            //System.out.println("en flag : " + enabledFlag.get(enab));
            
            //get method XInputGetStae in XInput1_4.dll
            // descriptor is returnType, Args in order
            // so XInputGetState return an int (DWORD) , takes an int (DWORD) and takes a structure address (&XINPUT_STATE)
            MethodHandle readem = nativeLinker.downcallHandle(
                    stdlibLookup.lookup("XInputGetState").or(() -> loaderLookup.lookup("XInputGetState")).orElseThrow(),
                    FunctionDescriptor.of(OfInt.JAVA_INT,OfInt.JAVA_INT,OfAddress.ADDRESS));


            int res = (int) readem.invoke(0, xin.address());// pad number - address of struct

            // 0 is good anything else is reason for failure  like 1167 = no gamepads found
            System.out.println("Res : " + res);
            
            // get left trigger value
            Integer LT = (int) LTrig.get(xin);
            System.out.println("ltrig : " + (LT + 256)%256); // normalise to 0 - 255
            
            // get buttons pressed
            int b = (short) buttons.get(xin);
            System.out.println("Buttons : " + b); // buttons is bitwise field for buttons pressed see below
        
        } catch (Throwable t) {
            System.out.println(t.getMessage());   //t.printStackTrace();
        }
    }
#End If

'XINPUT_GAMEPAD_DPAD_UP            0x0001
'XINPUT_GAMEPAD_DPAD_DOWN        0x0002
'XINPUT_GAMEPAD_DPAD_LEFT        0x0004
'XINPUT_GAMEPAD_DPAD_RIGHT        0x0008
'XINPUT_GAMEPAD_START            0x0010
'XINPUT_GAMEPAD_BACK            0x0020
'XINPUT_GAMEPAD_LEFT_THUMB        0x0040
'XINPUT_GAMEPAD_RIGHT_THUMB        0x0080
'XINPUT_GAMEPAD_LEFT_SHOULDER    0x0100
'XINPUT_GAMEPAD_RIGHT_SHOULDER    0x0200
'XINPUT_GAMEPAD_A                0x1000
'XINPUT_GAMEPAD_B                0x2000
'XINPUT_GAMEPAD_X                0x4000
'XINPUT_GAMEPAD_Y                0x8000

 

[Daestrum]

Another simple example (using java 22 will work in IDE) uses JavaObject Library

Calls the OS to get the current PID via Foreign Function interface

'Non-UI application (console / server application)
#Region Project Attributes 
    #CommandLineArgs:
    #MergeLibraries: True 
    #VirtualMachineArgs: --enable-native-access=ALL-UNNAMED
#End Region

Sub Process_Globals
    Dim thisPID As Int
End Sub

Sub AppStart (Args() As String)
    thisPID = getPID
    Log($"PID = ${thisPID}"$)
End Sub

Sub getPID As Object
    Return (Me).As(JavaObject).RunMethod("getMyPID",Null)
End Sub

#if java
import java.lang.invoke.*;
import java.lang.foreign.*;

public static Object getMyPID() throws Throwable {
    return Linker.nativeLinker().downcallHandle(
           Linker.nativeLinker().defaultLookup().find("_getpid").orElseThrow(),    
           FunctionDescriptor.of(ValueLayout.JAVA_INT))
           .invoke();
}
#End If