I think that I'll do a ui similar to ResEdit's/Resorcerer's. People are used to that the most, so there won't be any need to adjust to a new interface when switching. The only problem is that adding support for 48x48 icons when the Finder starts to use them will require me to design the whole interface. So this interface isn't very scalable, but it's familiar.
I started to implement this. The first step was to change the refreshing/editing from being hardcoded (of editing the 32 bit icon) to editing any selected pix map. I'll have two write 4 set pixel routines, for each of the bit depths (32, 8, 4 and 1). I also started to work on the user interface. I added a couple of controls, one which represents the 32 bit icon, and the other one the 8 bit mask. Then I added control tracking, so that when you click on one the 32 bit icon is set for editing, and for the other the 8 bit mask. However I haven't written the SetPixel8 routine, so you can only view the mask, attempting to edit it will result in a crash. But it's a start, and implementing the rest of the depths/sizes will simply be a mechanical job.