title: Material ripple effect hidden by other view in layout
body: <p>I added a ripple effect on a <code>ImageButton</code>, however it is hidden by an <code>ImageView</code> used as a background for the parent view <code>RelativeLayout</code>.</p>
  
  <p>Here's the layout file:</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                  xmlns:tools="http://schemas.android.com/tools"
                  android:layout_width="match_parent"
                  android:layout_height="172dp"
                  android:orientation="vertical"
                  android:theme="@style/ThemeOverlay.AppCompat.Dark"&gt;
  
      &lt;ImageView
          android:id="@+id/drawerBackgroundImageView"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:scaleType="centerCrop"
          android:src="@drawable/drawer_background"/&gt;
  
      [...]
  
      &lt;ImageButton
          android:id="@+id/drawerLogoutButton"
          android:layout_width="32dp"
          android:layout_height="32dp"
          android:layout_alignBottom="@id/drawerEmailTextView"
          android:layout_alignParentEnd="true"
          android:layout_alignParentRight="true"
          android:layout_marginEnd="@dimen/activity_horizontal_margin"
          android:layout_marginRight="@dimen/activity_horizontal_margin"
          style="@style/FlatButtonStyle"
          android:scaleType="centerInside"
          android:src="@drawable/ic_logout_white_24dp"/&gt;
  
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>(there's a bunch of other views but they're irrelevant here)</p>
  
  <p>I'm using an <code>ImageView</code> as the background for the <code>RelativeLayout</code> as I need to set a specific <code>scaleType</code> for the image, so I can't use the basic <code>android:background</code> property.</p>
  
  <p>The ripple effect is hidden as it doesn't have a mask layer (I want it to extend out of the button's bounds) and thus uses the <code>ImageButton</code>'s parent view to be displayed. The effect is perfectly visible if I remove the <code>ImageView</code>.</p>
  
  <p>Is there a way to get the ripple effect to be shown above the problematic <code>ImageView</code>?</p>