https://t.co/RHZKjvseIT https://t.co/RHZKjvseIT "I've decided to make pdf's of my ray tracing books available at "pay what you want". This can include zero, wh

https://t.co/RHZKjvseIT https://t.co/RHZKjvseIT "I've decided to make pdf's of my ray tracing books available at "pay what you want". This can include zero, which I encourage for students and any other cash-strapped people. 50% of gross proceeds will go to programming education non-for-profits." Peter Shirley https://twitter.com/Peter_shirley/status/984947257035243520 https://twitter.com/Peter_shirley/status/984947257035243520