how to fill a shape by Drag on that shape ?

hi , i’m trying to make a game in painting style .

like image above , i trying to display a shape to user on my game . user should be drag on this shape and Completely fill shape . but i have two problem on this :
#1 _ when user touch , just if user touch is on this shape , The shape begins to fill , on user touch position . how i can do it ?

Note : i can draw a line but can’t mask it on shape .

#2 _ how i can check , the shape is completely filled ?

thanks to all .

hello danielsalehi, have you found a way to make this work?