il link :
Drawable Resources | Android Developers per comodità vi copio il codice
example:
XML file saved at res/drawable/clip.xml:
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:drawable="@drawable/android"
android:clipOrientation="horizontal"
android:gravity="left" />
</shape>
The following layout XML applies the clip drawable to a View:
<ImageView
android:id="@+id/image"
android:background="@drawable/clip"
android:layout_height="wrap_content"
android:layout_width="wrap_content" />
The following code gets the drawable and increases the amount of clipping in order to progressively reveal the image:
ImageView imageview = (ImageView) findViewById(R.id.image);
ClipDrawable drawable = (ClipDrawable) imageview.getDrawable();
drawable.setLevel(drawable.getLevel() + 1000);
Increasing the level reduces the amount of clipping and slowly reveals the image. Here it is at a level of 7000:
Note: The default level is 0, which is fully clipped so the image is not visible. When the level is 10,000, the image is
not clipped and completely visible.