Support image rotation

[gildor]

We plan to use Telephoto as a foundation for image cropper, but Telephoto doesn't support image rotation (for side change or horizon level adjustment).

Because zoom already supported, it would be beneficial to support also rotation angle on level of Zoomable.

In terms of API, would be nice to support Content Scale for rotated photos too (so if zoom beyond rotated image area is allowed or not).

Additionally it may be considered to also support optional gesture rotation (otherwise it could be hard to implement without conflict with pinch to zoom)

[saket]

I'd love to support this. Wanna help me out?

I'm not sure what the API should look like, but we could start with a ZoomableState#rotateBy() function. Rotation values can be recorded in GestureState. You're right that we'll also need to adjust the rotated content's scale to ensure it fits within its bounds.

Additionally it may be considered to also support optional gesture rotation (otherwise it could be hard to implement without conflict with pinch to zoom)

I agree -- I've been passively wanting to solve this for some time now (#26). The only blocker is the coerceWithinContentBounds() function used here. It currently uses the content's top-left coordinates as its pivot point, but to support rotations, it will need to be changed to the center.

[gildor]

Yes, our team would love to help with it, let us look into the code