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I'm trying to use purely JNA to create a borderless window and also control its size. I can create the window using this:

String windowClass = new String("NewWindowClass");
HMODULE hInst = Kernel32.INSTANCE.GetModuleHandle("");

WNDCLASSEX wClass = new WNDCLASSEX();
wClass.hInstance = hInst;
wClass.lpfnWndProc = Main.this;
wClass.lpszClassName = windowClass;
User32.INSTANCE.RegisterClassEx(wClass);

HWND hWnd = User32.INSTANCE.CreateWindowEx(User32.WS_EX_TOPMOST, windowClass, "This is the window title", 0, 0, 0, 50, 50, null, null, hInst, null);
User32.INSTANCE.ShowWindow(hWnd, 1);

The 50, 50 being the width and height of the window. This was sourced from some JNA demo code (lines 54-74). I can remove the borders by adding this code after it:

long style = User32.INSTANCE.GetWindowLong(hWnd, User32.GWL_STYLE);
style &= (~User32.WS_CAPTION);
User32.INSTANCE.SetWindowLong(hWnd, User32.GWL_STYLE, (int) style);

So now you can see that there's an un-decorated window, however unlike the expected 50x50 dimensions, the size still seems to be affected by the caption bar and border but I just don't know how to stop it. I tried a bunch of windows styles and extended window styles with no luck.
Just to be sure I could get it the way I wanted, I created a simple JFrame:

 JFrame frame = new JFrame("Title");
 frame.setUndecorated(true);
 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 frame.setSize(50, 50);
 frame.setVisible(true);

Using Microsoft Spy++, I cross referenced the window styles to make sure they matched and even with the same styles, I just couldn't get it to change to the size I want it. So I'm guessing this isn't something to do with the window styles but I don't know where to go from here. Anyone have any info on this?

Thanks in advance.