title: Change transperency of main screen on DrawerLayout menu open
body: <p>I am using Drawer Layout on my application's home screen to provide some menu options. when drawer opens I want to add some gradient or some invisibility to background activity. How can I do that?
  I have used below two methods but it wont work and visibility od main screen remains same </p>
  
  <pre><code>mDrawerLayout.setDrawerShadow(getDrawable(R.drawable.loading_top_bar), GravityCompat.START);
  </code></pre>
  
  <p>and</p>
  
  <pre><code>mDrawerLayout.setScrimColor() Method
  </code></pre>
  
  <p>From both methods screen behind NavigationDrawer is clearly visible, I want to blur it so that it's visible but not clear</p>