Originally Posted by Offler
According to my knowledge about capabilities of GCN architecture, Accelerated RayTracing was possible years ago. Previously it was CPU operated - if present and used entirely only for shadow generation.
The discussion whether it will be "realtime" eg >30fps on a given resolution is of a different kind, because there is dozens of questions about how many rays there actually is. Typical shading operations usually used rays as well, but it was like... one ray for entire surface or object.
It depends on what you mean by "possible." The algorithms have been around for decades, but the raw computational requirements make a practical implementation very difficult. To do a decent job, you not only need to trace rays, you need to trace the scattered rays that happen when the first ray hits an object. The simple implementation is just specular reflections: one ray in, one ray out. To do diffuse reflections properly, to get the sort of ambient lighting that we're used to from real objects but never see in rendered imagery, that takes doing things like one ray in, a hundred rays out. Every time a ray, or a scattered ray, hits a surface, you multiply the total number.
You see how that might present a scaling problem.
The raytrace calculation, itself, is incredibly simple. You start with a 3-D spatial map with all the surfaces, you generate a bi-directional reflection distribution function (includes both specular and diffuse) for each surface, you start with some source rays each with a vector and intensity, and you point them in straight lines until they hit things. At each surface, the BRDF describes how many rays at which angles and with what intensity should come off of the surface based on the incident ray, and so you add those new rays to your list of rays to be traced and you keep going. Modern optical design software can handle the huge numbers of rays required for proper stray light analysis, and this sort of modeling is required to make quality optical systems. To use it in games is simply put the correct way to handle lighting, because it has the highest fidelity and is closest to reality.
That people got grumpy about Nvidia's stupid pricing for the RTX series does not change the technical superiority of raytracing for lighting simulation, no matter whose color is on the box.