title: How to implement an eraser tool in a simple drawing app?
body: <p>I have a prototype of a simple drawing application. When the user drags a finger across the screen, I record the points along the way and draw a series of lines between them. In other words, a drawing is a list of “paths” and each path is a list of points to connect. This is easy, it works and it’s efficient.</p>
  
  <p>The problem is I’d like to implement an eraser tool. In a regular bitmap editor the eraser simply erases pixels, but in my drawing there are no pixels to erase – all pixels are created dynamically by stroking the paths. I could do a simple eraser by “drawing” using the background colour, overlaying the already painted paths. But I’d like to draw on a textured background, so that’s a no-go.</p>
  
  <p>How would you do this? (Short of the obvious solution of representing the drawing as a bitmap where the eraser is simple.)</p>