A better one with Swift,

https://www.amazon.com/Metal-Programming-Guide-Tutorial-Refe...

There is a better one, focused on Swift.

https://www.amazon.com/Metal-Programming-Guide-Tutorial-Refe...

For the rest, yes, WWDC videos, samples, and then documentation, by this order.

I picked up this book by Janie Clayton, it's pretty good: https://www.amazon.co.uk/Metal-Programming-Guide-Tutorial-Re...