title: Forward based ray tracer in C++
body: <p>I am making a Ray Tracer in C++, and need it to be forward based (source to detector) instead of backwards based (detector to source). I need this as I am using it to model particular materials and their properties when interacting with light.</p>
  
  <p>There are a lot of Ray Tracing tutorials available for backward direction, which is understandable as it makes more sense when writing ray tracing for graphics purposes, but I can not find any good ones for forward direction tracing (light source to detector.)</p>
  
  <p>Does anyone know of any good forward based tutorials, or have a forward based ray tracer that they wouldn't mind me building on for non-profit purposes?</p>