Understanding Android's <layer-list>

Question

I don't understand how the layer-lists work. I read the official documentation with some examples but it does not work for me like expected. I want four squares which should be padded with 1dp, but nothing is like expected. Here is a screenshot scaled by 500%:

^{(The wrong colors do not matter)}
As you can see the size is completely wrong and the paddings are missing. I tried to set real values like width/height and right/left/top/buttom to be sure that android get the point what I want.

Here is my xml:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:top="0dp" android:left="0dp" android:bottom="0dp" android:right="0dp">
        <shape android:shape="rectangle">
            <size android:width="9dp"
                android:height="9dp"/>
            <solid android:color="#f000"/>
        </shape>
    </item>

    <item android:top="1dp" android:left="1dp" android:bottom="5dp" android:right="5dp">
        <shape android:shape="rectangle">
            <size android:width="3dp"
                android:height="3dp"/>
            <solid android:color="#f00"/>
        </shape>
    </item>
    <item android:top="1dp" android:left="5dp" android:bottom="5dp" android:right="1dp">
        <shape android:shape="rectangle">
            <size android:width="3dp"
                android:height="3dp"/>
            <solid android:color="#0f0"/>
        </shape>
    </item>

    <item android:top="5dp" android:left="1dp" android:bottom="1dp" android:right="5dp">
        <shape android:shape="rectangle">
            <size android:width="3dp"
                android:height="3dp"/>
            <solid android:color="#0f0"/>
        </shape>
    </item>
    <item android:top="5dp" android:left="5dp" android:bottom="1dp" android:right="1dp">
        <shape android:shape="rectangle">
            <size android:width="3dp"
                android:height="3dp"/>
            <solid android:color="#f00"/>
        </shape>
    </item>
</layer-list>

Answer 1

Either you use px instead of dp or multiply all dimensions by 10.

I'm ashamed to admit that I don't exactly know WHY this is happening but my guess is that it has something to do with densities where 1dp is a floating px value and the ImageView is scaled up.

Expert answer is welcomed :)

Answer 2

The values for left, top, right and bottom are measured from their respective edge.

So left=0dp, top=0dp, bottom=0dp & right=50dp will give you a rectangle that is (match_parent - 50dp) wide and not 50dp wide. Therefore larger values for "right" will actually give you a smaller rectangle.

The same would apply to the other value, but these would behave as expected in most cases, its just "right" that might cause confusion.