@Override
    public void readFrameBuffer(FrameBuffer fb, ByteBuffer byteBuf) {
        readFrameBufferWithGLFormat(fb, byteBuf, GL.GL_RGBA, GL.GL_UNSIGNED_BYTE);
    }
Copy the source buffer to the destination buffer, including both color
and depth.

@param src the source buffer (unaffected)
@param dst the destination buffer
jme3-core/src/main/java/com/jme3/renderer/opengl/GLRenderer.java