Tower defence game, angle shooting by touch

Hello. I’ve got an idea for some tower defence game. I’m checking how the mechanics works on android development, because I’m newbie at android scripting etc…

I want something like this

When the player starts touching on the screen, gun starts shooting too. When the player is going to slide down his finger, the angle of shooting is going to change(while touching).

Everything is on the picture(xD)

Sorry for my bad english, regards…

What is the question?