spacedoubt
You can do what you described like this,at least for the first part that is.
https://dl.dropboxusercontent.com/u/542 ... w_rot.capx
The bounding box of a rotated triangle can be found by adding an image point at each corner of the triangle and then finding the min and max horizontally and vertically.
And like you said you can make the bounding box only update after rotation. The only tricky part was positioning the bounding box while rotating, but there's a useful formula for that here:
https://www.siggraph.org/education/mate ... 2drota.htm
And while I was at it I added the ability to rotate around any point for little extra effort,
The only aspect of that can't be done is resizing in relation to the screen, as that would introduce skewing, which C2 can't do. So you'd be limited to only resizing relative to the object.
Edit:
Here it is working with multiple objects. Shirt click to toggle selection.
https://dl.dropboxusercontent.com/u/542 ... multi.capx