I just tried your PR and the functionality works as advertised, great 👍

For the current feature-set I'd like to suggest the following changes

zoom

• I think the center of zooming should be:
  • a) the center of the screen, if invoked by the toolbar buttons
  • b) the position of the mouse pointer, if invoked by the scroll wheel
• to change the center of the zooming operation, you need to translate the chosen center to the left-top corner, then zoom and then translate back

pan

• the pan speed should be equal to the mouse speed
• on my screen it seems that the canvas moves "slower" than the mouse moves
• that might have something to do with the scale factor (?)

Usability and UI

• we need to discuss whether we want toolbar buttons, an extra toolbar or none
• we may want to respond to the arrow buttons for panning
• we may want to respond to the zooming gesture for zooming
• I think we want a shortcut to reset all zoom and translation
• we need to think how the background looks like - black or white (or any other color)
• we do want to export/save the "smallest possible canvas", that still covers the image and all drawings. That allows users to draw outside the image
• I didn't look at the code yet 🙈

Is there any blocker for this to merged? I've looking forward for this feature.
I could take a shot at fixing any problems in this changes if @mattrobineau is not able rn, since I'm interested in get this working

I don't currently have the bandwidth to continue working on this. If you would like to take over, please feel free.

The current state of this PR adds working panning however the zooming is not currently working correctly. The zoom button works fine, however the zoom under cursor is not completed.