Editing is destructive

[mmaismma]

Current thumbnail-maker is all functional. But the changes you make cannot be undone i.e. the editing is destructive. The example shown below explains this a lot.

• Step 1: Add a background image(optional but it helps contrast the issue)
  
• Step 2: Add episode number. In this case, I typed 40 as the episode number.
  
• Step 3: Change the episode number. I changed it to 24 in this case.
  
  Where you expect '24' to replace '40', it overwrites it. The same is also true for the background image and HermitCraft logo.
  Making editing non-destructible is all good.

[mmaismma]

Currently, the canvas only draws the updated element. A possible solution for this issue is to re-draw the whole canvas on every update.