Unlimited canvas painting program

[markotaht at gmail.com]

How to create a program similar to paint, but the difference would be that the cursor would be always in the middle and the canvas moves or the camera is always fixed on the cursor as it moves around the canvas. And the canvas should be infinite. What would be reasonable to use? 

In addition, i want it to draw a line whidout me having to press a button, just move the mouse.

Ill try to think a better way to describe, what i want, but for now i hope this is sufficient and clear enough.