Question

I found this code. This is supposed to read framebuffer and save it as a png file.

It’s giving the error:

eglCreateWindowSurface() can only be called with an instance 
of SurfaceView or SurfaceHolder at the moment, this will be fixed later.

Code:

    private EGL10 egl;
    private EGLDisplay display;
    private EGLConfig config; 
    private EGLSurface surface;
    private EGLContext eglContext;
    private GL11 gl;
    //private GL10 gl10;
    protected int width, height;
    Bitmap mSavedBM;

    public void Take(Context context)
    {
        Display display= ((WindowManager) context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();        
        int screenWidth = display.getWidth();
        int screenHeight = display.getHeight();     
        String SCREENSHOT_DIR = "/sdcard/screenshots";
        initGLFr(); //GlView initialized.
        savePixels( 0, 10, screenWidth, screenHeight, gl); //this gets the screen to the mSavedBM.
        saveBitmap(mSavedBM, SCREENSHOT_DIR, "capturedImage");
    }

    private void initGLFr()
    {
        egl = (EGL10) EGLContext.getEGL();
        display = egl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);
        int[] ver = new int[2];
        egl.eglInitialize(display, ver);
        int[] configSpec = {EGL10.EGL_NONE};
        EGLConfig[] configOut = new EGLConfig[1];
        int[] nConfig = new int[1];
        egl.eglChooseConfig(display, configSpec, configOut, 1, nConfig);
        config = configOut[0];
        eglContext = egl.eglCreateContext(display, config, EGL10.EGL_NO_CONTEXT, null);
        surface = egl.eglCreateWindowSurface(display, config, SurfaceHolder.SURFACE_TYPE_GPU, null);
        egl.eglMakeCurrent(display, surface, surface, eglContext);
        gl = (GL11) eglContext.getGL();
    }

    public void savePixels(int x, int y, int w, int h, GL10 gl)
    {
        if (gl == null)
        {
            return;         
        }
        synchronized (this)
        {
            if (mSavedBM != null) 
            {
                mSavedBM.recycle();
                mSavedBM = null;
            }
        }
        int b[] = new int[w * (y + h)];
        int bt[] = new int[w * h];
        IntBuffer ib = IntBuffer.wrap(b);
        ib.position(0);
        gl.glReadPixels(x, 0, w, y + h, GL10.GL_RGBA,GL10.GL_UNSIGNED_BYTE,ib);
        for (int i = 0, k = 0; i < h; i++, k++)
        {
            //OpenGLbitmap is incompatible with Android bitmap
            //and so, some corrections need to be done.
            for (int j = 0; j < w; j++)
            {
                int pix = b[i * w + j];
                int pb = (pix >> 16) & 0xff;
                int pr = (pix << 16) & 0x00ff0000;
                int pix1 = (pix & 0xff00ff00) | pr | pb;
                bt[(h - k - 1) * w + j] = pix1;
            }
        }
        Bitmap sb = Bitmap.createBitmap(bt, w, h, Bitmap.Config.ARGB_8888);
        synchronized (this)
        {
            mSavedBM = sb;
        }
    } 

    static String saveBitmap(Bitmap bitmap, String dir, String baseName) 
    {
        try 
        {
            File sdcard = Environment.getExternalStorageDirectory();
            File pictureDir = new File(sdcard, dir);
            pictureDir.mkdirs();
            File f = null;
            for (int i = 1; i < 200; ++i)
            {
                String name = baseName + i + ".png";
                f = new File(pictureDir, name);
                if (!f.exists()) 
                {
                    break;
                }
            }
            if (!f.exists()) 
            {
                String name = f.getAbsolutePath();
                FileOutputStream fos = new FileOutputStream(name);
                bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
                fos.flush();
                fos.close();
                return name;
            }
        }
        catch (Exception e) {} 
        return null;
    }

}

QUESTION:

Does this code take screenshots at a time when my application is in background or if it only makes screenshots of my application?

Answer 1

You can’t take screenshots (that would be a security vulnerability), only system apps can do it.
This method will most likely save a black PNG.