PorterduffXfermode: Clear a section of a bitmap

I don't see anything unexpected. In the particular case of Mode.CLEAR, both the color and alpha of the destination are cleared, which allows the black background to show. This utility allows one to experiment with various modes, colors and alpha values, and the source may offer some insight. In the (somewhat dated) image below, the CLEAR areas reveal the faint pinstripe-gray provided by the platform's PanelUI delegate.

_{(source: Composite at sites.google.com)}

The problem is hardware acceleration. Turn it OFF for the particular View that you are painting with CLEAR. If you're using a custom view, do this in the constructors:

if (android.os.Build.VERSION.SDK_INT >= 11) 
{
     setLayerType(View.LAYER_TYPE_SOFTWARE, null);
}

You can also call setLayerType on a view reference.