If you're talking about accurately simulating optical effects, you have to ray trace.
Nope! Ray tracing is classified as an image-order algorithm. It is still (and perhaps only) possible to get object -> image one-to-one accuracy without a purely image-order algorithm.
Also, this is false despite the existence of alternative algorithmic approaches that share the premises of ray tracing (i.e. discrete light paths). If you want to talk about accurately simulating optical effects, ray tracing should be considered a naive hack. Speaking of ray tracing as a mapping rather than an algorithm, it's a messy injection of light paths into screen-space (whereas a similar technique such as beam tracing is a more accurate). It's absurd to call this accuracy. It's brutal.
The importance of object-space in the prospects of accuracy is demonstrated here (in application to ray tracing; from the aspect of mapping): http://www.cs.uaf.edu/~genetti/Research ... 93/GI.html
Correctness is a different matter. Nevertheless, for the record, many raytracers fail to be physically correct.
Quite. Shortcuts are great. As long as I can get the result I want, I'll happily shave cycles off my rendering routines for use elsewhere. I probably didn't make that clear in my post.
Indeed. Inherently, a shortcut is merely a path of execution which arrives at the same destination but in shorter time.
It's interesting that Hugo states that raytracers tend to only calculate one bounce for each object in the scene.
Actually, he makes a comparison between radiosity and the Monte Carlo methods of global illumination. Most old raytracers don't implement any diffuse multi-bounce because it would either be horrendously slow to render on old hardware, or without a large increase in sampled rays, it would be pointless. To the contrary, it's pretty easy to simulate multi-bounce specular reflections as long as they are perfectly sharp and not glossy. This is the 'classic' raytraced look.
I'm pretty sure that I remember seeing a setting for a bounce limit in many of my rendering packages. Obviously, you have to limit the bounces to render the scene in a reasonable time, but turning up the value produced better images and more accurate reflections.
Me too. From my experience, accounting for "multiple bounces" does not necessarily produce global illumination. Although the simulation of multiple bounces is elemental to the principle of global illumination, I have found that even if a raytracer follows multiple bounces, it may be insufficient for a realistic global illumination effect. There's a lot more to distribution than merely recurrence (what you're distributing and where it is distributed e.g. irradiance and BDRFs). This is where "the Monte Carlo method" is relevant to the topic of global illumination in the context of raytracing.Let's make a clarification:
Ray tracing is not the only technique that models discrete light paths. Also on the behalf of my opinions: in terms of accuracy, image-space is simply inferior to object-space. In terms of performance, I think image-order rendering is usually inferior to object-order, although this comparison is heavily dependent on the situation of the renderer. I believe that it is necessary to develop a new hybrid method.