I’m so glad you’re enjoying it!
I would be great to have another book with extra topics, but at the moment, I don’t believe one is in the pipeline. That’s not to say that there won’t be, and your feedback definitely helps 
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We had a post about picking: Detect tap on a mesh - as I wrote there, when I’ve needed to, I have assigned objects a color and then written the objects to a texture, then work out coordinates on a screen touch and read the color from the texture which gives the object hit. rumour had another method with ray casting.