Different results of Android Support Library's CardView on different devices

Question

Playing with Android Support Library v7 widget CardView I see different results on a Galaxy S4 comparing to a Nexus 4 device. Having the following layout:

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/card_view"
    android:layout_width="fill_parent"
    android:layout_height="150dp"
    android:layout_gravity="center"
    android:layout_marginTop="8dp"
    android:layout_marginBottom="10dp"
    android:layout_marginLeft="20dp"
    android:layout_marginRight="20dp"
    android:orientation="horizontal"
    card_view:cardCornerRadius="7dp"
    card_view:cardElevation="12dp">

    <ScrollView
        android:id="@+id/scrollView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_centerVertical="true">

        <TextView
            android:id="@+id/txtExample"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/no_messages" />

    </ScrollView>

</android.support.v7.widget.CardView>

I got these results:

Nexus 4 (5.0.1):

Samsung Galaxy S4 (4.4.2):

It seems that the one on Nexus calculates the View with it's margins, and then the paints the shadow outside. On the other hand, the one of Samsung seems to apply margins and then paint the shadow inside until it reaches the calculated View's bounds.

Am I missing something?

Answer 1

All your observations are correct :)
Everything is explained well on official documentation of CardView:

Before L, CardView adds padding to its content and draws shadows to that area. This padding amount is equal to maxCardElevation + (1 - cos45) * cornerRadius on the sides and maxCardElevation * 1.5 + (1 - cos45) * cornerRadius on top and bottom.

and:

Note that, if you specify exact dimensions for the CardView, because of the shadows, its content area will be different between platforms before L and after L. By using api version specific resource values, you can avoid these changes. Alternatively, If you want CardView to add inner padding on platforms L and after as well, you can set setUseCompatPadding(boolean) to true.

As described there - you should just use setUseCompatPadding (true) then outer padding on both: L and pre-L will be the same.