Features to make cropping faster

[jdchristensen]

Is your feature request related to a problem? Please describe.

I do a lot of cropping of my photos, and like to flip through many photos and quickly crop them sometimes before even deciding which ones to keep. For example, I might have a sequence of bird-in-flight photos with the subject in different positions, and it's hard to compare them at 100% since the subject in is a different position in each image. So it's handy if I can make cropping very efficient.

Describe the solution you'd like

1. It would be great to be able to resize the cropping rectangle using the mouse wheel, maybe with a modifier. This would be similar to how masks can be scaled using the mouse wheel. The rescaling should be relative to the position the mouse pointer is at, aiming to get that point to be the center when the rectangle gets small enough.
2. Sometimes I'd like to be able to manually drag a rectangle (constrained to the currently active aspect ratio) instead of resizing the default one which fills the full area. This could be done by dragging left mouse with a modifier key, or maybe dragging middle or right mouse. (Right mouse makes some sense since this action deletes the existing rectangle, which is what right click does.)
3. Often the best rectangle for the current image is similar to a recently used one. It would be great if I could flip through the recently used crop rectangles with some keystrokes. Usually the last one used will be close, and I'll just need to alter it a bit, so this often would be a single keystroke and a single mouse drag to slightly recenter.

I've seen features like these in other software and I think they would be pretty natural to have in darktable.

Alternatives

Copying and pasting a crop from one photo to a group of others gets partway to 3, but requires more advance planning and is less interactive.

Additional context

Thanks for considering this!