Read the depth buffer of OpenGL ES on Android
<p>I am trying to read the depth buffer in OpenGL ES on Android, but all the values are zero.
Can someone explain why is that.</p>

<pre><code>    public void onSurfaceChanged(GL10 unused, int width, int height) {
    // Adjust the viewport based on geometry changes,
    // such as screen rotation
    GLES20.glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
    GLES20.glClearDepthf(1.0f);
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);

    GLES20.glEnable(GLES20.GL_DEPTH_TEST);
    GLES20.glDepthMask( false );

    GLES20.glViewport(0, 0, width, height);

    float ratio = (float) width / height;

    // this projection matrix is applied to object coordinates
    // in the onDrawFrame() method
    Matrix.frustumM(mProjectionMatrix, 0, -ratio, ratio, -1, 1, 4, 9);
}
</code></pre>

<p>Read the depth buffer:</p>

<pre><code>        FloatBuffer buffer = FloatBuffer.allocate(720*945);
    GLES20.glReadPixels(0, 0, 720, 945, GLES20.GL_DEPTH_COMPONENT, GLES20.GL_FLOAT, buffer);
    float[] depth = buffer.array();
    for (int i = 0; i &lt; 720*945; i++){
            Log.i("Depth", ""+depth[i]);
    }
</code></pre>

<p>The model has been draw on screen:
<a href="http://i.stack.imgur.com/Dpd7Y.png" rel="nofollow">ScreenShot</a></p>

<p><strong>EDIT</strong></p>

<p>I was moved my project to ES 3.0. I create a FrameBuffer, color and depth texture and then attach.I get error GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT </p>

<pre><code> GLES30.glEnable(GLES30.GL_TEXTURE_2D);

    GLES30.glGenTextures(1, colorTex, 0);
    GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, colorTex[0]);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_WRAP_S, GLES30.GL_CLAMP_TO_EDGE);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_WRAP_T, GLES30.GL_CLAMP_TO_EDGE);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MAG_FILTER, GLES30.GL_NEAREST);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MIN_FILTER, GLES30.GL_NEAREST);
    GLES30.glTexImage2D(GLES30.GL_TEXTURE_2D, 0, GLES30.GL_RGBA, fboWidth, fboHeight, 0, GLES30.GL_RGBA, GLES30.GL_FLOAT, null);

    GLES30.glGenTextures(1, depthTex, 0);
    GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, depthTex[0]);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_WRAP_S, GLES30.GL_CLAMP_TO_EDGE);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_WRAP_T, GLES30.GL_CLAMP_TO_EDGE);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MAG_FILTER, GLES30.GL_NEAREST);
    GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MIN_FILTER, GLES30.GL_NEAREST);
    GLES30.glTexImage2D(GLES30.GL_TEXTURE_2D, 0, GLES30.GL_DEPTH_COMPONENT24, fboWidth, fboHeight, 0, GLES30.GL_DEPTH_COMPONENT, GLES30.GL_FLOAT, null);


    GLES30.glGenFramebuffers(1, fb, 0);
    GLES30.glBindFramebuffer(GLES30.GL_FRAMEBUFFER, fb[0]);

    GLES30.glFramebufferTexture2D(GLES30.GL_FRAMEBUFFER, GLES30.GL_COLOR_ATTACHMENT0, GLES30.GL_TEXTURE_2D, colorTex[0], 0);

    checkStatus("Color Test");

    GLES30.glFramebufferTexture2D(GLES30.GL_FRAMEBUFFER, GLES30.GL_DEPTH_ATTACHMENT, GLES30.GL_TEXTURE_2D, depthTex[0], 0);

    checkStatus("Depth Test");

}
</code></pre>

<p>Q1: How can I resolve above error?</p>

<p>Q2: How to check the depth value in depth texture </p>