Desktop Capture using LWJGL

Question

I want to create an application using to capture desktop and save it to a file.

I went through a few LWJGL codes for this. However it only captures OpenGL window.

Here are the code snippets I used.

private static void screenShot(){
    //Creating an rbg array of total pixels
    int[] pixels = new int[WIDTH * HEIGHT];
    int bindex;
    // allocate space for RBG pixels
    ByteBuffer fb = ByteBuffer.allocateDirect(WIDTH * HEIGHT * 3);

    // grab a copy of the current frame contents as RGB
    GL11.glReadPixels(0, 0, WIDTH, HEIGHT, GL11.GL_RGB, GL11.GL_UNSIGNED_BYTE, fb);

    BufferedImage imageIn = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);
    // convert RGB data in ByteBuffer to integer array
    for (int i=0; i < pixels.length; i++) {
        bindex = i * 3;
        pixels[i] =
            ((fb.get(bindex) << 16))  +
            ((fb.get(bindex+1) << 8))  +
            ((fb.get(bindex+2) << 0));
    }
    //Allocate colored pixel to buffered Image
    imageIn.setRGB(0, 0, WIDTH, HEIGHT, pixels, 0 , WIDTH);

    //Creating the transformation direction (horizontal)
    AffineTransform at =  AffineTransform.getScaleInstance(1, -1);
    at.translate(0, -imageIn.getHeight(null));

    //Applying transformation
    AffineTransformOp opRotated = new AffineTransformOp(at, AffineTransformOp.TYPE_BILINEAR);
    BufferedImage imageOut = opRotated.filter(imageIn, null);

    try {//Try to screate image, else show exception.
        File output1 = new File("image.png"); 
        ImageIO.write(imageOut, "PNG" , output1);
    }
    catch (Exception e) {
        System.out.println("ScreenShot() exception: " +e);
    }
}

Another one I tried was:

public static BufferedImage glScreenshot() {
    GL11.glReadBuffer(GL11.GL_FRONT);
    int w = Display.getDisplayMode().getWidth();
    int h = Display.getDisplayMode().getHeight();
    int bpp = 4;
    ByteBuffer buffer = BufferUtils.createByteBuffer(w * h * bpp);

    GL11.glReadPixels(0, 0, w, h, GL11.GL_RGBA, GL11.GL_UNSIGNED_BYTE, buffer);

    BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);

    for (int x = 0; x < w; x++) {
        for (int y = 0; y < h; y++) {
            int i = (x + (w * y)) * bpp;
            int r = buffer.get(i) & 0xFF;
            int g = buffer.get(i + 1) & 0xFF;
            int b = buffer.get(i + 2) & 0xFF;
            image.setRGB(x, h - (y + 1), (0xFF << 24) | (r << 16) | (g << 8) | b);
        }
    }

    return image;
}

Is it even possible to capture the desktop using LWJGL?

Answer 1

You cannot capture desktop using LWJGL or OpenGL. Opengl only processes it's own frame buffer, which it in turn, prints on the screen. Anything that's not in the frame buffer (or in your own program somewhere), such as other programs, the desktop, etc, are never passed to OpenGL, so it cannot read that data. However, java.awt has a class which lets you capture the screen. See here .