Canvas update
![e-2](https://user-images.githubusercontent.com/38907008/43991069-dfe3af6a-9d9f-11e8-88e7-5a51a2f599e7.jpg)
![e-1](https://user-images.githubusercontent.com/38907008/43991073-e2c82986-9d9f-11e8-8363-6000d1a8ff16.JPG)

I want to move this line (on control) when get any input .  
so I searched and tried some ways that I can imagine, but I could not do it.

I think that canvas should update to achieve that.
How can I update canvas?
(I am sorry for my poor English..)