Starting near the end of the second section of Lesson 1, the .cpp file extension is used instead of .mm. <img width="130" alt="Screenshot 2023-12-31 at 5 18 25 PM" src="https://github.com/wmarti/MetalTutorial/assets/84483508/e6a6df61-c999-4ce0-9d7e-c83ad31815a7">