Android source code not working, reading frame buffer through glReadPixels

Question

Hi,

I am new to Android development and have an assignment to read frame buffer data after a specified interval of time.

I have come up with the following code:

public class mainActivity extends Activity { Bitmap mSavedBM; private EGL10 egl; private EGLDisplay display; private EGLConfig config;
private EGLSurface surface; private EGLContext eglContext; private GL11 gl; protected int width, height;

 //Called when the activity is first created. 
@Override
public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);

    // get the screen width and height
    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);
    int screenWidth = dm.widthPixels;
    int screenHeight = dm.heightPixels; 

    String SCREENSHOT_DIR = "/screenshots";
    initGLFr(); //GlView initialized.
    savePixels( 0, 10, screenWidth, screenHeight, gl); //this gets the screen to the mSavedBM.
    saveBitmap(mSavedBM, SCREENSHOT_DIR, "capturedImage");

    //Now we need to save the bitmap (the screen capture) to some location.
    setContentView(R.layout.main); //This displays the content on the screen

}
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) {

    } finally {

        //if (fos != null) {
         //   fos.close();
       // }

    }
    return null;
}

}

Also, if some one can direct me to better way to read the framebuffer it would be great. I am using Android 2.2 and virtual device of API level 8. I have gone through many previous discussions and have found that we can not know read frame buffer directly throuh the "/dev/graphics/fb0".

Thanks, Muhammad Ali

Answer 1

problem solved, regarding the execution of the above code. But still I could not read the frame buffer data.

I have searched and read in depth the internals and traced all the previous claims about accessing framebuffer although on older version Android pre 1.5. that at present we can not access the framebuffer.

The porting on Android pre 1.5 does have posts on accessing directly through /dev/fb0. This does not work for later additions though and the Android Development team has no plans either as mentioned by them in android google groups.

I hope this helps a lot of people spending a lot of their time to figure about a way.

regards, Muhammad Ali Rajput