The block previews used by Tidy TileMapper (generated while you build Blocks using the Block Editor) are created using the following process:
- The object in question is placed in the scene.
- A special Preview Camera is setup.
- Tidy TileMapper takes a screenshot through this Camera.
- The object is removed.
- The screenshot is saved in the Previews directory for later use.
- The scene is reverted to its original form.
I thought about this - and did test it, but the results (and its undocumented nature) are too unpredictable.