how to make skin display on top of visualisation or video preview in order to give a transparent effect? (like in pm3's home.xml)
xbmc renders each piece of the skin in the order they are placed in the respective window's .xml file. in this case inside pm3's home.xml the control that creates the visualization
<control>
<type>visualization</type>
...
...
</control>
comes before the transparent background
<control>
<type>image</type>
...
...
</control>
simply layer your skin in the order you wish