jna Pointer in 32 bit JRE

I am using jna to call Magnification api functions in Java.

MagImageScalingCallback.java

package jna.extra;

import com.sun.jna.Callback;
import com.sun.jna.Pointer;
import com.sun.jna.platform.win32.WinDef.HRGN;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.platform.win32.WinDef.RECT;

public interface MagImageScalingCallback extends Callback{
    public Boolean MagImageScalingCallback(HWND hwnd, Pointer srcdata,MAGIMAGEHEADER srcheader, Pointer destdata,MAGIMAGEHEADER destheader,RECT source,RECT clipped,HRGN dirty);
}

MAGIMAGEHEADER.java

package jna.extra;

import java.util.Arrays;
import java.util.List;

import com.sun.jna.platform.win32.Guid.GUID;


public class MAGIMAGEHEADER extends com.sun.jna.Structure {
    public int width;
    public int height;
    public GUID format;
    public int stride;
    public int offset;
    public int cbsize;

    public List getFieldOrder() {
        return Arrays.asList("width","height","format","stride","offset","cbsize");
    }
}

Magnification.java

package jna.extra;

import com.sun.jna.Native;
import com.sun.jna.platform.win32.WinDef.DWORD;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.platform.win32.WinDef.RECT;
import com.sun.jna.win32.StdCallLibrary;
import com.sun.jna.win32.W32APIOptions;


public interface Magnification extends StdCallLibrary {

    Magnification INSTANCE = (Magnification) Native.loadLibrary("magnification", Magnification.class,
                                                W32APIOptions.DEFAULT_OPTIONS);

    public Boolean MagInitialize();

    public boolean MagSetWindowFilterList(HWND hwndMag, DWORD dword, int i,
            HWND[] excludeHWNDs);

    public boolean MagSetWindowSource(HWND hwndMag, RECT sourceRect);

    public void MagGetWindowFilterList(HWND hwndMag, DWORD dword, int i, HWND[] test);

    public boolean MagSetImageScalingCallback(HWND hwndMag,MagImageScalingCallback MagImageScalingCallback);

    public MagImageScalingCallback MagGetImageScalingCallback(HWND hwndMag);

}

WinGDIExtra.java

package jna.extra;

import com.sun.jna.platform.win32.WinDef.DWORD;
import com.sun.jna.platform.win32.WinGDI;

public interface WinGDIExtra extends WinGDI {

    public DWORD SRCCOPY = new DWORD(0x00CC0020);
    public DWORD SRCPAINT = new DWORD(0x00ee0086);
    public DWORD SRCAND = new DWORD(0x008800c6);
    public DWORD SRCINVERT = new DWORD(0x00660046);
    public DWORD SRCERASE = new DWORD(0x00440328);

    public DWORD NOTSRCCOPY = new DWORD(0x00330008);
    public DWORD NOTSRCERASE = new DWORD(0x001100a6);
    public DWORD MERGECOPY = new DWORD(0x00c000ca);
    public DWORD MERGEPAINT = new DWORD(0x00bb0226);

    public DWORD PATCOPY = new DWORD(0x00f00021);
    public DWORD PATPAINT = new DWORD(0x00fb0a09);
    public DWORD PATINVERT = new DWORD(0x005a0049);
    public DWORD DSTINVERT = new DWORD(0x00550009);
    public DWORD WHITENESS = new DWORD(0x00ff0062);
    public DWORD BLACKNESS = new DWORD(0x00000042);
    public DWORD CAPTUREBLT = new DWORD(0x00CC0020 | 0x40000000);
    public DWORD Black = new DWORD(0x00000000);

    public long WS_CHILD = 0x40000000L;
    public long WS_VISIBLE = 0x10000000L;
    public long MS_SHOWMAGNIFIEDCURSOR = 0x0001L; 


    public long WS_EX_TOPMOST = 0x00000008L;
    public long WS_EX_LAYERED = 0x00080000;
    public long WS_EX_TRANSPARENT = 0x00000020L;

    public long WS_CLIPCHILDREN = 0x02000000L;

    public long MW_FILTERMODE_EXCLUDE = 0;

}

My code

package jna.extra;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

import com.sun.jna.platform.win32.Kernel32;
import com.sun.jna.platform.win32.WinDef.DWORD;
import com.sun.jna.platform.win32.WinDef.HRGN;
import com.sun.jna.platform.win32.WinDef.RECT;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.Native;
import com.sun.jna.Pointer;

import luz.winapi.jna.User32;

public class screenSkip {

    public static void main(String[] args){
        if(!Magnification.INSTANCE.MagInitialize()){
            System.out.println("Cannot Intialize Magnification API");
            System.exit(0);
        }

        RECT desktopRect= new RECT();
        HWND desktop = User32.INSTANCE.GetDesktopWindow();
        if(desktop==null){
            System.out.println("Problem with Desktop");
            System.exit(0);
        }
        if(!User32Extra.INSTANCE.GetWindowRect(desktop, desktopRect)){
            System.err.println("Cannot get window rect");
            System.exit(0);
        }
        HWND top = User32Extra.INSTANCE.CreateWindowEx(new DWORD(WinGDIExtra.WS_EX_TOPMOST | WinGDIExtra.WS_EX_LAYERED | WinGDIExtra.WS_EX_TRANSPARENT), "#32770", "Parent Window", new DWORD(WinGDIExtra.WS_CLIPCHILDREN), desktopRect.left, desktopRect.top, desktopRect.right-desktopRect.left, desktopRect.bottom-desktopRect.top, desktop, null, null, null);

        if(top==null){
            System.out.println("Problem while creating Parent Window and the error is "+Native.getLastError());
            System.exit(0);
        }

        HWND hwndMag=null;
        System.out.println(Native.getLastError());
        hwndMag = User32Extra.INSTANCE.CreateWindowEx(null, "Magnifier", "MagWindow", new DWORD(WinGDIExtra.WS_CHILD | WinGDIExtra.MS_SHOWMAGNIFIEDCURSOR | WinGDIExtra.WS_VISIBLE), desktopRect.left, desktopRect.top, desktopRect.right-desktopRect.left, desktopRect.bottom-desktopRect.top, top, null, Kernel32.INSTANCE.GetModuleHandle(null), null);
        if(hwndMag==null){
            System.err.println("Problem while creating Magnifier Window and the error is "+Native.getLastError());
            System.exit(0);
        }

        RECT sourceRect= new RECT();

        if(!User32Extra.INSTANCE.GetWindowRect(desktop, sourceRect)){
            System.err.println("Cannot get window rect");
            System.exit(0);
        }

        final BufferedImage image = new BufferedImage(1366, 768, BufferedImage.TYPE_INT_RGB);
        if(!Magnification.INSTANCE.MagSetImageScalingCallback(hwndMag,new MagImageScalingCallback() {

            public Boolean MagImageScalingCallback(HWND hwnd, Pointer srcdata,
                    MAGIMAGEHEADER srcheader, Pointer destdata,
                    MAGIMAGEHEADER destheader, RECT source, RECT clipped, HRGN dirty) {
                image.setRGB(0, 0, srcheader.width, srcheader.height, srcdata.getIntArray(0, srcheader.width * srcheader.height ), 0, srcheader.width);
                return true;
            }
        })){
            System.err.println("Error occured while setting callback");
            System.exit(0);
        }
        if (!Magnification.INSTANCE.MagSetWindowSource(hwndMag, sourceRect))
        {
            System.err.println("Cannot copy");
            System.exit(0);
        }
        try {
            ImageIO.write(image, "JPEG", new File("printed1.jpg"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (!Magnification.INSTANCE.MagSetWindowSource(hwndMag, sourceRect))
        {
            System.err.println("Cannot copy");
            System.exit(0);
        }
    }
}

If the MagSetWindowSource function is called the MagImageScalingCallback function is called.

The problem is if I run this code with jre7(64 bit) everything works fine. But if I run the same code in jre7(32 bit), I am getting the following error.

#
# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x10002a21, pid=5552, tid=4884
#
# JRE version: Java(TM) SE Runtime Environment (7.0_80-b15) (build 1.7.0_80-b15)
# Java VM: Java HotSpot(TM) Client VM (24.80-b11 mixed mode, sharing windows-x86 )
# Problematic frame:
# C  [jna6797525900717560222.dll+0x2a21]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# If you would like to submit a bug report, please visit:
#   http://bugreport.java.com/bugreport/crash.jsp
# The crash happened outside the Java Virtual Machine in native code.
# See problematic frame for where to report the bug.
#

Stack: [0x05c60000,0x05cb0000],  sp=0x05cae4d0,  free space=313k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
C  [jna6797525900717560222.dll+0x2a21]
j  com.sun.jna.Pointer._getInt(J)I+0
j  com.sun.jna.Pointer.getInt(J)I+6
j  com.sun.jna.Pointer.getValue(JLjava/lang/Class;Ljava/lang/Object;)Ljava/lang/Object;+340
j  com.sun.jna.Structure.readField(Lcom/sun/jna/Structure$StructField;)Ljava/lang/Object;+168
j  com.sun.jna.Structure.read()V+82
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.convertArgument(Ljava/lang/Object;Ljava/lang/Class;)Ljava/lang/Object;+330
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.invokeCallback([Ljava/lang/Object;)Ljava/lang/Object;+95
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.callback([Ljava/lang/Object;)Ljava/lang/Object;+2
v  ~StubRoutines::call_stub
V  [jvm.dll+0x1429aa]
V  [jvm.dll+0x20743e]
V  [jvm.dll+0x142a2d]
V  [jvm.dll+0xcb7b2]
V  [jvm.dll+0xcd5df]
C  [jna6797525900717560222.dll+0x9dd2]
C  [jna6797525900717560222.dll+0xa47f]
C  [jna6797525900717560222.dll+0xc864]
C  [jna6797525900717560222.dll+0xcdee]
C  0x00b80012
C  [magnification.dll+0x5434]
C  [magnification.dll+0x5a2c]
C  [magnification.dll+0x5f5d]
C  [magnification.dll+0x612a]
C  [magnification.dll+0x28ab]
C  [USER32.dll+0x162fa]
C  [USER32.dll+0x16d3a]
C  [USER32.dll+0x1965e]
C  [USER32.dll+0x196c5]
C  [magnification.dll+0x22e2]
C  [jna6797525900717560222.dll+0xcc77]
C  [jna6797525900717560222.dll+0xc78a]
C  [jna6797525900717560222.dll+0x4561]
C  [jna6797525900717560222.dll+0x4d2e]
j  com.sun.jna.Function.invokeInt(I[Ljava/lang/Object;)I+0
j  com.sun.jna.Function.invoke([Ljava/lang/Object;Ljava/lang/Class;Z)Ljava/lang/Object;+315
j  com.sun.jna.Function.invoke(Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+214
j  com.sun.jna.Library$Handler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+341
j  com.sun.proxy.$Proxy5.MagSetWindowSource(Lcom/sun/jna/platform/win32/WinDef$HWND;Lcom/sun/jna/platform/win32/WinDef$RECT;)Z+20
j  org.redfire.screen.ScreenShare$CaptureScreen.run()V+674
j  java.lang.Thread.run()V+11
v  ~StubRoutines::call_stub
V  [jvm.dll+0x1429aa]
V  [jvm.dll+0x20743e]
V  [jvm.dll+0x142b75]
V  [jvm.dll+0x142bd7]
V  [jvm.dll+0xed5cf]
V  [jvm.dll+0x163c4c]
V  [jvm.dll+0x1646a7]
V  [jvm.dll+0x1a92f9]
C  [msvcr100.dll+0x5c556]
C  [msvcr100.dll+0x5c600]
C  [kernel32.dll+0x133aa]
C  [ntdll.dll+0x39f72]
C  [ntdll.dll+0x39f45]

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j  com.sun.jna.Pointer._getInt(J)I+0
j  com.sun.jna.Pointer.getInt(J)I+6
j  com.sun.jna.Pointer.getValue(JLjava/lang/Class;Ljava/lang/Object;)Ljava/lang/Object;+340
j  com.sun.jna.Structure.readField(Lcom/sun/jna/Structure$StructField;)Ljava/lang/Object;+168
j  com.sun.jna.Structure.read()V+82
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.convertArgument(Ljava/lang/Object;Ljava/lang/Class;)Ljava/lang/Object;+330
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.invokeCallback([Ljava/lang/Object;)Ljava/lang/Object;+95
j  com.sun.jna.CallbackReference$DefaultCallbackProxy.callback([Ljava/lang/Object;)Ljava/lang/Object;+2
v  ~StubRoutines::call_stub
j  com.sun.jna.Function.invokeInt(I[Ljava/lang/Object;)I+0
j  com.sun.jna.Function.invoke([Ljava/lang/Object;Ljava/lang/Class;Z)Ljava/lang/Object;+315
j  com.sun.jna.Function.invoke(Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+214
j  com.sun.jna.Library$Handler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+341
j  com.sun.proxy.$Proxy5.MagSetWindowSource(Lcom/sun/jna/platform/win32/WinDef$HWND;Lcom/sun/jna/platform/win32/WinDef$RECT;)Z+20
j  org.redfire.screen.ScreenShare$CaptureScreen.run()V+674
j  java.lang.Thread.run()V+11
v  ~StubRoutines::call_stub

How to solve this issue? How can I make this work on a 32-bit JRE? Thanks!

Firstly, the MagImageScalingCallback is defined as a WINAPI function, which means you have to define the callback as being a child of StdCallCallback.

Secondly, the return type is a simple boolean (you should not use Boolean for this).

Thirdly, the parameters of the callback are MAGIMAGEHEADER, and not MAGIMAGEHEADER *, and the RECT is not a RECT *, which means they needs to be passed by value; so the callback declaration needs to be changed like so:

I added a RectByValue class, containing the following:

import com.sun.jna.platform.win32.WinDef;
import com.sun.jna.Structure;

public class RectByValue extends WinDef.RECT implements Structure.ByValue {}

I changed the MagImageScalingCallback class with the following:

import com.sun.jna.win32.StdCallLibrary;

public interface MagImageScalingCallback extends StdCallLibrary.StdCallCallback {
   public boolean MagImageScalingCallback(HWND hwnd, Pointer srcdata,MAGIMAGEHEADER.ByValue srcheader, Pointer destdata,MAGIMAGEHEADER.ByValue destheader,RectByValue source,RectByValue clipped,HRGN dirty);
}

You will need to add ByValue support to MAGIMAGEHEADER; and also use a SIZE_T for the last element of the structure:

import java.util.Arrays;
import java.util.List;

import com.sun.jna.platform.win32.Guid.GUID;
import com.sun.jna.platform.win32.BaseTSD;
import com.sun.jna.Pointer;
import com.sun.jna.Structure;

public class MAGIMAGEHEADER extends Structure {
    public int width;
    public int height;
    public GUID format;
    public int stride;
    public int offset;
    public BaseTSD.SIZE_T cbsize;

    public List getFieldOrder() {
        return Arrays.asList("width","height","format", "stride","offset","cbsize");
    }

    public static class ByValue extends MAGIMAGEHEADER implements Structure.ByValue {
        public ByValue() {}

        public ByValue(MAGIMAGEHEADER magimageheader) {
            super (magimageheader.getPointer());

            width = magimageheader.width;
            height = magimageheader.height;
            format = magimageheader.format;
            stride = magimageheader.stride;
            offset = magimageheader.offset;
            cbsize = magimageheader.cbsize;
        }

        public ByValue(Pointer memory) {
            super(memory);
        }
    }

    public MAGIMAGEHEADER(Pointer memory) {
        super(memory);
        read();
    }

    public MAGIMAGEHEADER() {
    }
}

I changed the screen size to match my display on screenSkip so it's new BufferedImage(2160, 1440... instead of 1366, 786, and changed the callback code creator to:

if(!Magnification.INSTANCE.MagSetImageScalingCallback(hwndMag, new MagImageScalingCallback() {

    public boolean MagImageScalingCallback(HWND hwnd, Pointer srcdata,
            MAGIMAGEHEADER.ByValue srcheader, Pointer destdata,
            MAGIMAGEHEADER.ByValue destheader, RectByValue source, RectByValue clipped, HRGN dirty) {
        image.setRGB(0, 0, srcheader.width, srcheader.height, srcdata.getIntArray(0, srcheader.width * srcheader.height ), 0, srcheader.width);
        return true;
    }
})){
    System.err.println("Error occured while setting callback");
    System.exit(0);
}

The end product of running this in 32bit or 64bit mode is a file called This is about as minimal as I can think will achieve what you want.

.... huh ... it gives me a blank image on 32bit. That seems incorrect.