How to sketch or draw a shaded paintings in Android 2.2?

I have worked on Paint in my app. It works fine normally. What i need is, If User wish to draw something like shaded paintings or shadow diagrams then if he/she clicks the shaded button then they must be able to draw the shaded diagrams. How to do this?

VIDEO : Shaded paintings in Android

Like this above video, the User must be able to draw shaded paintings. I have googled a lot about this. No link i have found :(

Any links or examples or articles are there for this app?

Any ideas or suggestions would be highly appreciated, thanks !

This isn't really as "shader" question. However....

The app you're indicating saves a record of where the pen has been. In certain (user-selected) circumstances, as the pen moves the app will quickly draw lots of faint lines between the current pen location and selected other previous pen locations.

The modes described are different tunings of the way the lines are drawn, and of the rules for adding these lines.

Hope that gets you on your way -- you could rough-out something like this in html5 or processing very quickly to teach yourself a lot about the dynamics, I'm sure.