I’m working on a Java application where I want to create a transparent, non-clickable window with only a clickable button. To manipulate the window’s native properties, I am using JNA (Java Native Access) to call functions from user32.dll. However, I’m encountering issues with loading and using certain functions from the DLL.

Here’s the scenario:

Transparent Window: I’m using SetLayeredWindowAttributes to make the window transparent.
Non-Clickable Area: I need to use CreateRectRgnA and SetWindowRgn to make the window non-clickable outside the button area.
Clickable Button: I’ve added a button that should remain functional, and it works as expected.
The problem is that some functions, specifically CreateRectRgnA, SetWindowRgn, and SetLayeredWindowAttributes, are throwing errors when I try to call them using JNA. For example:

Error 1: I get an UnsatisfiedLinkError when trying to load user32.dll.

Error 2: Functions like SetWindowRgn and CreateRectRgnA are not
working as expected.

Error 3: I receive a java.lang.NullPointerException when attempting to
access specific native function calls.

 import com.sun.jna.Native;
import com.sun.jna.platform.win32.WinDef;
import com.sun.jna.platform.win32.WinUser;
import javax.swing.*;
import java.awt.*;

public class NonClickableWindowWithButton {
    public static void main(String[] args) {
        // Create the window (JFrame without decoration)
        JFrame window = new JFrame("Non-Clickable Window");
        window.setUndecorated(true); // Remove title bar and borders
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setSize(400, 300);
        window.setLocationRelativeTo(null);

        // Make the window transparent
        window.setBackground(new Color(0, 0, 0, 0)); // Fully transparent
        window.setLayout(new FlowLayout());

        // Add a clickable button
        JButton button = new JButton("Clickable");
        button.addActionListener(e -> System.out.println("Button clicked!"));
        window.add(button);

        // Make the window visible
        window.setVisible(true);

        // Make the window non-clickable, except for the button
        makeWindowNonClickable(window);
    }

    private static void makeWindowNonClickable(JFrame window) {
        User32 user32 = User32.INSTANCE;
        WinDef.HWND hwnd = getHWND(window);

        if (hwnd == null) {
            System.err.println("Unable to get the window handle.");
            return;
        }

        // Make the window transparent to clicks
        int exStyle = user32.GetWindowLong(hwnd, WinUser.GWL_EXSTYLE);
        user32.SetWindowLong(hwnd, WinUser.GWL_EXSTYLE, exStyle | WinUser.WS_EX_LAYERED | WinUser.WS_EX_TRANSPARENT);
    }

    private static WinDef.HWND getHWND(JFrame window) {
        return new WinDef.HWND(Native.getComponentPointer(window));
    }
}

interface User32 extends com.sun.jna.platform.win32.User32 {
    User32 INSTANCE = Native.load("user32", User32.class);

    int GetWindowLong(WinDef.HWND hwnd, int nIndex);

    int SetWindowLong(WinDef.HWND hwnd, int nIndex, int dwNewLong);
}