Something I've noticed within a lot of gaming enthusiast communities is a tendency for people to adopt terminology used in computer science or game development and then use said terminology based on their own intuition instead of putting forth the effort to research and understand the significance of the terms they use on a fundamental level. This kind of behavior results in a lot of widespread misinformation, and the next thing you know, entire conversations among the public conscious revolve around complete misconceptions.My goal with this thread (and subsequent related threads) is to provide clear distinctions on terminology used in this industry, as well as easy-to-understand comparisons between the techniques video games use to approximate real life phenomena, and actual real-life phenomena.For the first topic in this series, I'm going to talk about Volumetric Lighting.There seems to be a lot of confusion about this effect, probably due to very different implementations of it used in modern games today. However, the biggest issue I've noticed regarding Volumetric Lighting is, ironically, the name itself. You see, when we consider the behavior of light as it pertains to the real world, it doesn't really make sense to call it 'volumetric'. Everything we see is the result of the sub-surface scattering of photons that are eventually reflected directly into our eyes. Whatever light we are able to see is no longer at the point that it originated if we can see it, and is not contained within any medium where it can be considered to have volume. So why call light volumetric if light doesn't actual have any massive volume? Well, just because it isn't actually volumetric, it doesn't mean that it can't appear that way sometimes, and that's exactly why we use that term in the first place.The concept behind Volumetric Lighting as it's used in most video games is based on real life phenomena called crepuscular rays, as you can see here:Although the shafts of light that you see in the picture above appear to converge towards a single point, that is in fact, a perspective illusion. The rays of light that have traveled from the sun and entered the Earth's atmosphere are actually nearly parallel to each other, but our brains interpret parallel lines from such great distances as convergent. More importantly, however, is that these shafts of light aren't really shafts of light at all. What we consider to be shafts of light are actually just distinct reflections of atmospheric particulate matter. When matter approaches a physical size that is comparable to the wavelength of the light that it's scattering, as opposed to sizes larger or smaller than that wavelength, it is known as Mie Scattering.Here are other examples of Mie Scattering:Now you might be wondering what's the difference between light's behavior during general mie scattering and light's behavior during crepuscular ray formation, because clearly we can see that crepuscular rays have visible shafts that appear to radiate from the light source, while general mie scattering does not. Well, there is one crucial difference, and that is that crepuscular rays form the appearance of shafts due to objects (clouds, in this case) obstructing the pathway for light to travel. These obstructions result in the clouds casting shadows, and the shadows subsequently providing contrast to the light that is able to travel through the openings in the clouds and illuminate the atmospheric particulate matter below. The contrast between alternating patterns of light and dark (or very bright light and not as bright light) is what causes our brains to perceive the illuminated particulates as 'light shafts', but I can assure you, light is not just sitting there suspended in these massive, volumetric media. The atmospheric particular matter is what is volumetric and suspended in the air.It is extremely important to understand the relationship between mie scattering and the formation of light shafts, because without the participating media that causes mie scattering to occur in the first place, it is impossible to see light shafts, as there would be nothing for light to interact with on a scale that allows for this particular phenomenon to take place. Which leads me to my main point; Volumetric Lighting in video games.So if you've been able to follow along this far, you have probably realized that particulates like fog or haze are pretty necessary in order to see light shafts, yet many video game developers do not take this into consideration at all. Instead, developers will focus on the effect as our brains perceive it; light shafts (also known as god rays). These days, the god rays are simply rendered as a screen-space effect based on the depth buffer information for a given frame. The atmospheric conditions don't even matter; whenever the sun is on-screen, the game will magically produce god rays through spaces where objects aren't obstructing a direct view of the sun. It has been such a staple in the industry that many people don't even question how unnatural or unrealistic it is to have god rays without any participating media to cause the effect in the first place. There are exceptions to this industry trend, however, which I will cover shortly.Here are some comparisons between the Volumetric Lighting solution used in the Witcher 3, and the Volumetric Lighting solution used in Deus Ex: Mankind Divided:Witcher 3 (light source on screen)Witcher 3 (light source off-screen)Mankind Divided (light source on screen)Mankind Divided (light source off-screen)As you can see, the approach to representing Volumetric Lighting is very different between both games. The Witcher 3's solution is to focus on the god rays themselves, artistically designing their appearance to look mie scattered, per god ray. However, these shafts cannot persist beyond the line of sight of the light source, due to how screen space techniques work on a fundamental level. This is not how it works in the real world, as I've explained before. Mankind Divided's solution is much more realistic and much closer in its appearance to the crepuscular rays we can see in the real world. Instead of selectively rendering god rays, the engine approximates a mie scattering effect for a given scene, and renders depth shadows in mid-air that serve to contrast between the particulates that the light rays are able to reach, and the particulates that the light rays are unable to reach, due to surfaces that obstruct the pathways of the light rays, which naturally provide the illusion of light shafts.Unfortunately, neither the solution used in Mankind Divided, or nature's very own crepuscular rays are nearly as glamorous and defined as the god rays seen in games like Witcher 3, so the screen-space solution has remained the industry standard for now (not to mention it's simply a cheaper solution). One of the problems with Mankind Divided's solution, in terms of how it affects the consumer experience, is that developers have less control over how the light shafts appear, if they even appear at all. In fact, some people believed and complained that the Volumetric Lighting feature in Mankind Divided was removed altogether upon release, as it was not very prominent. In reality, however, it was merely a case of many scenes in the game not having enough mie scattering in the atmosphere in order for light shafts to take effect; it was completely dependent on the atmospheric conditions in a given scene, so if there were no atmospheric particulates for that scene, there was no Volumetric Lighting. This was especially true for the lack of sunbeams, since there wasn't a lot of mie scattering near the horizon. Nevertheless, the final version of the game does indeed have Volumetric Lighting, under the right conditions. Despite the realism though, it's not always the most ideal route to take for a developer who wants a lot of control over the visual representation of their game.At any rate, the main take away from this OP is that you cannot always interpret terminology literally, especially in computer science. Light does not have volume in the sense that we define volume, though it can appear that way under the right conditions (like interacting with atmospheric particulate matter). More importantly, please take the above facts into consideration when judging the quality of Volumetric Lighting in a game. The most prominent examples of it may not be the most realistic or computationally taxing, and the more realistic examples may not be the most ideal for all developers.And that concludes my first topic on Virtual vs. Reality. Stay tuned for the next topic, coming soon!