It's easy. There is a web-site.
Ray tracing simulator: https://ricktu288.github.io/ray-optics/simulator/
I have no idea who runs the site, nor do I know how accurate it is.
But the guy who wrote it did a bang-up job. It helps a lot.
But it really can answer what happens to the light as it travels through the coverglass or hits an object.
Rules are simple and with a little practice you can figure it out.
In this picure you can see an 18 degree point source hitting a nearly flat lens at an angle and then reflecting.
Try it - you wiil be impressed.
