JNA screenshot game

Question

Need to make screenshot of some games. Found this JNA code, but when I try to do screen`s I just get black screen. When I try to do screen of some program, like WordPad ot smth it works well. As well I am bad in JNA, I want ask you about help. Is it possible to accomplish this task ?

public class Paint extends JFrame {
public BufferedImage capture(HWND hWnd) throws IOException {
    String gettime = Gettime.screentime();
    HDC hdcWindow = User32.INSTANCE.GetDC(hWnd);
    HDC hdcMemDC = GDI32.INSTANCE.CreateCompatibleDC(hdcWindow);
    RECT bounds = new RECT();
    User32Extra.INSTANCE.GetClientRect(hWnd, bounds);
    int width = bounds.right - bounds.left;
    int height = bounds.bottom - bounds.top;

    HBITMAP hBitmap = GDI32.INSTANCE.CreateCompatibleBitmap(hdcWindow, width, height);
    HANDLE hOld = GDI32.INSTANCE.SelectObject(hdcMemDC, hBitmap);
    GDI32Extra.INSTANCE.BitBlt(hdcMemDC, 0, 0, width, height, hdcWindow, 0, 0, WinGDIExtra.SRCCOPY);
    GDI32.INSTANCE.SelectObject(hdcMemDC, hOld);
    GDI32.INSTANCE.DeleteDC(hdcMemDC);
    BITMAPINFO bmi = new BITMAPINFO();
    bmi.bmiHeader.biWidth = width;
    bmi.bmiHeader.biHeight = -height;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 32;
    bmi.bmiHeader.biCompression = WinGDI.BI_RGB;
    Memory buffer = new Memory(width * height * 4);
    GDI32.INSTANCE.GetDIBits(hdcWindow, hBitmap, 0, height, buffer, bmi, WinGDI.DIB_RGB_COLORS);

    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    image.setRGB(0, 0, width, height, buffer.getIntArray(0, width * height), 0, width);
    GDI32.INSTANCE.DeleteObject(hBitmap);
    User32.INSTANCE.ReleaseDC(hWnd, hdcWindow);
    File outputfile = new File("C:\\image" +gettime+ ".jpg");
    ImageIO.write(image, "jpg", outputfile);
    return image;
}

public static void main(String[] args) throws IOException {

        new Paint();

}
BufferedImage image;

public Paint() throws IOException {
    HWND hWnd = User32.INSTANCE.FindWindow(null, "some game");
    this.image = capture(hWnd);

    setDefaultCloseOperation(EXIT_ON_CLOSE);
    pack();
    setExtendedState(MAXIMIZED_BOTH);
    setVisible(true);
}
@Override
public void paint(Graphics g) {
    super.paint(g);
    g.drawImage(image, 20, 40, null);
}
}

Answer 1

Using JNA to take a screenshot sounds utterly complicated, besides not being platform-agnostic. Java has built-in functionality to take screenshots using the Robot class:

import java.awt.Robot;

Rectangle screenRect = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
BufferedImage capture = new Robot().createScreenCapture(screenRect);
ImageIO.write(capture, "png", new File("./screenshot.png"));

By adjusting the screenRect you could also just take a screenshot of a portion of the screen.

Answer 2

GDI32Util.getScreenshot(HWND hwnd)

Method is already provided in jna.

but my case is as the same as you.... the game screen is black... nothing...