I need one object to mimic shape of another, so that it would fit it's volume and shape. Circle (2d) needs to be shaped like those crooked cube. As if you put something soft into some hard box, I need changed circle, cube is just for shaping (preferably for Blender 2.8, but not necessarily).
Here is a try with some shapekeys:
- Create your object, a circle if it begins with a circle.
- In the Properties panel > Data > Shape Keys, create a basic shapekey, then a second one.
- Switch to Edit mode, select the second shapekey and edit your mesh, make it a bent square.
- Now back to Object mode, if you play with the shapekey Value you can morph from a shape to the other.
- Make a box
- Make a circle which fits the box
- Make a Lattice object which fits the box
- Assign a Lattice modifier to the circle and the box
Now, whatever you do to the lattice, will happen to the circle and the box.
Or, if you have to fit to an existing box, make the Lattice to fit the circle, and then snap its vertices to the box.