Crop sprites at runtime, What's the best method?

Hello everyone! I was making a game similar to The Tower. https://youtu.be/_IYdYekZGSQ?t=58s

I was wondering how to implement the system that they are using for cropping the tower block textures.

I had thought about creating many sprites, and changing them as the width of block decreases over time, what other ways are there? Thanks a lot!