Windows thumbnail preview with JNA (Java)

Question

W32API.HWND targetHwnd = User32.INSTANCE.FindWindow('SunAwtFrame', 'Frame')
W32API.HWND sourceHwnd = User32.INSTANCE.FindWindow('triuiScreen', 'EVE')
W32API.HANDLE thumbnailH = new W32API.HANDLE()

NativeLibrary dwm = NativeLibrary.getInstance('dwmapi')
dwm.getFunction('DwmRegisterThumbnail').invoke(targetHwnd, sourceHwnd, thumbnailH)

gives me

# A fatal error has been detected by the Java Runtime Environment:
#
#  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x70f34bee, pid=7208, tid=7364
#
# JRE version: 6.0_18-b07
# Java VM: Java HotSpot(TM) Client VM (16.0-b13 mixed mode, sharing windows-x86 )
# Problematic frame:
# C  [DWMAPI.DLL+0x4bee]

I have a feeling I'm doing it completely wrong, but digging in documentation got me nowhere.

Answer 1

The 3rd param is an "out" parameter, and needs to be a pointer to the handle, not the handle itself. So, something like

dwm.getFunction('DwmRegisterThumbnail')
  .invoke(targetHwnd, sourceHwnd, new PointerByReference(thumbnailH))