I'm making an image editor app for phones with touchscreens. It will have tools that are similar to related desktop applications like brush, pencil, rubber, mask, smudge, crop, text etc. tools.
For a fluid workflow, I think these are important:
on small screens especially, most of the space on the screen should be dedicated to the image editing area and things like toolbars.
the user needs to be able to quickly switch between certain tools with minimal fuss. I imagine being able to quickly shift between the brush and eraser tool and being able to quickly press undo/redo would be important when drawing something for instance.
I think GIMP and Inkscape's toolbar based interface work well for these kinds of applications but there's just no room for huge toolbars on small screens.
I already have a toolbar at the top of the screen that has room for about 7 or 8 shortcut icons including the basics like undo and redo as this seems like a simple way to give one click access to operations. Without making the toolbar huge, there's only enough room for a handful of other icons.
I'm looking for ideas on how to make the best use of this space.
Some ideas I've had:
Make half of the toolbar horizontally scrollable so you can swipe left/right to make other tool buttons visible. This seems fiddly and hard to discover and isn't great if you regularly use one tool that appears on the far left and another on the far right.
Reduce the number of tools by combining some. For example pencil and smudge become configurable modes of the brush tool. This can be unintuitive in some cases and introduces extra steps to switch between pencil and brush mode (but if this is rare this isn't a big deal).
Allow the user to change which tools appear in the toolbar so the user can decide which tools they can switch between quickly. For example by double tapping an icon they can be shown a menu that lets them swap the toolbar button for another tool. This has similarities to the previous point.
Is there anything obvious I'm missing?