Ray tracing

https://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Not in OpenGL: http://stackoverflow.com/questions/3667218/ray-tracing-in-modern-opengl-where-do-i-begin

Closed source implementations:

https://en.wikipedia.org/wiki/OptiX, NVIDIA

Open source implementations:

https://embree.github.io/ https://github.com/embree/embree

Hardware implementation

https://en.wikipedia.org/wiki/Ray-tracing_hardware

Imagination bought Caustic in 2010 from ex Apple engineers. CEO mentions it in 2015 interview: https://youtu.be/7rpXL8TFLlw?t=1701