How can you get the handle of a chrome process in java using JNA

Question

I am new to JNA, and I need to take a screenshot of a chrome window using java and JNA, I already have the function for taking screenshots of a given window using this code:

  public BufferedImage capture(WinDef.HWND hWnd) {

    WinDef.HDC hdcWindow = User32.INSTANCE.GetDC(hWnd);
    WinDef.HDC hdcMemDC = GDI32.INSTANCE.CreateCompatibleDC(hdcWindow);



    WinDef.RECT bounds = new WinDef.RECT();
    User32Extra.INSTANCE.GetClientRect(hWnd, bounds);

    int width = bounds.right - bounds.left;
    int height = bounds.bottom - bounds.top;

    WinDef.HBITMAP hBitmap = GDI32.INSTANCE.CreateCompatibleBitmap(hdcWindow, width, height);

    WinNT.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);

    WinGDI.BITMAPINFO bmi = new WinGDI.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);

    return image;

}

then I use the following code to save the bufferedImage:

     BufferedImage image;

     WinDef.HWND hWnd = User32.INSTANCE.FindWindow(null, "notepad - untitled");
                image = capture(hWnd);
                File outputfile = new File("image.jpg");
                try {
                    ImageIO.write(image, "jpg", outputfile);
                } catch (IOException e) {
                    e.printStackTrace();
                }

this works for some applications, e.g. notepad but not for chrome, for chrome it just throws a Illegal Argument Exception cause the program is trying to capture a screenshot with a width and height which are basically 0 since the process wasn't found, the full exception is this:

Exception in thread "JavaFX Application Thread" java.lang.IllegalArgumentException: Allocation size must be greater than zero
at com.sun.jna.Memory.<init>(Memory.java:111)
at de.xliquid.stadiarpc.Main.capture(Main.java:103)
at de.xliquid.stadiarpc.Main$1.run(Main.java:56)
at com.sun.javafx.scene.KeyboardShortcutsHandler.processAccelerators(KeyboardShortcutsHandler.java:347)
at com.sun.javafx.scene.KeyboardShortcutsHandler.dispatchBubblingEvent(KeyboardShortcutsHandler.java:163)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3964)
at javafx.scene.Scene$KeyHandler.access$1800(Scene.java:3910)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:2040)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2501)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:217)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:149)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleKeyEvent$357(GlassViewEventHandler.java:248)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:247)
at com.sun.glass.ui.View.handleKeyEvent(View.java:546)
at com.sun.glass.ui.View.notifyKey(View.java:966)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$152(WinApplication.java:177)
at java.lang.Thread.run(Thread.java:748)

I tried using the current title of chrome but that didn't work, and I think the best solution would be to just get the handle of chrome's first tab. Sadly I don't really know where to start here. Can anyone tell me what I could do? Thanks in advance.

Answer 1

JNA's WindowUtils class can be helpful here. The getAllWindows() method will return a List<DesktopWindow> where each DesktopWindow instance includes both a title (to match up with your Chrome process) and the HWND handle to that window.

The DesktopWindow also has a Rectangle with location and size dimensions, so you can copy the appropriate dimensions from the desktop itself, such as this simple one-liner:

BufferedImage screenShot = new Robot().createScreenCapture(rectangle);

Answers to this StackOverlow Question identify multiple other options for taking a screenshot of the entire window; simply substitute the Rectangle you derive from the DesktopWindow class appropriately (or use your own code above with the rectangle's dimensions).

Alternately, if you don't need all the information from the WindowUtils class, you could more directly use the WinAPI's EnumWindows function to directly iterate the windows and capture only the information that you need. This is the function WindowUtils uses internally, so its source code would be a good starting point to simplify from.