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Analysis Game Dev Digital Foundry - Tech Focus: Global Illumination - What It Is, How Does It Work And Why Do We Need It?

Jun 1, 2021
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I remeber there was a conversation about global illumination in a ray tracing thead a few weeks and there seemed a lot of confusion with some about it actually was, I did try explain that it wasn't new and there was different ways of simulating global illumnation but it may well be simpler to watch this video for anybody who doesn't understand what it is.

 

cormack12

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Mar 21, 2013
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Global illumination


Exhaustive luminescence
 
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Armorian

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Real Time GI should be mandatory in current gen games, consoles have enough power. At least in open world games, liner titles can get away with baked GI.
 
Jan 3, 2021
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fair to say, metro exodus ee with pure global illumination looked fantastic, i also hope to see more of it going forward
 

Negotiator101

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Jan 24, 2021
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That is actually a really nice summary of why RT is so important going forward or rather what kind of limitations you face if you don`t use it.

I´ll just link this video every time I see another "RT doesn`t matter" idiot from now on.
It's also very demanding on hardware, is it worth the tradeoff? The answer to that would change from game to game I would imagine. Certainly calling people idiots for a difference of opinion is not the way to go.
 

Haggard

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Nov 25, 2020
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It's also very demanding on hardware, is it worth the tradeoff?
Watch the video again. It`s a resounding yes, as long as you`re not targeting a very abstract or comppletely static look or are extremely power limited. See Metro Exodus EE (on PC) for example.
Certainly calling people idiots for a difference of opinion is not the way to go.
RT has been the standard for any klnd of light in CGI for decades and it is to this day the only way to get light right without making everything static. People belittling RT absolutely are idiots because their opinion completely ignores the technical facts. No developer would ever bother with lightmaps and co again if we all had enough power for RT in all games. RT or derivates thereof like Voxel-GI / Lumen will become the standard for anything that is within our power limit, simply because it is by far the best solution.
 
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Jun 1, 2021
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No graphical techniques shoudl ever be mandatory, it's far better that it's left to the artisist and technical team to asses the best use of resources.
Also, it's worth pointing out that no game does global illumination accurately, there are always shortcuts that have to be taken to get the games to run on the available hardware. That's even true with high end offline rendering. For global illumination to be done accurately it would need an almost infinite number of rays and it would also need to calulate how much energy is used by each photon each time it comes into contact with something, how much energy is left in the photon once it leaves the object, was other objects does the photon come into contact with after it's left the first object, how much is absorbed by the second point of contact and how much is bounced off again, etc. etc.
Even with that, it's really oversimplifiying what would need to be done achieve it accurately.
"Faking it" has always been a large part of computer rendering and it likely aalways will be.
 

Bulletbrain

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Dec 12, 2020
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^obviously even the most top drawer offline rendering techniques are "faking" it to some extent. But RT is an objectively better technique at simulating how light behaves (I'm talking technically and not artistically mind). It also makes the life of an artist that much more easier vs. having to figure out by eye where to place fake point lights to get the look they want. The roadblock was always performance; we are finally approaching that threshold where we have enough raw power and other ways to mitigate performance loss via good upscaling/FSR/DLSS. In that sense, the industry moving to a GI workflow is inevitable.
 

Negotiator101

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Watch the video again. It`s a resounding yes, as long as you`re not targeting a very abstract or comppletely static look or are extremely power limited. See Metro Exodus EE (on PC) for example.

RT has been the standard for any klnd of light in CGI for decades and it is to this day the only way to get light right without making everything static. People belittling RT absolutely are idiots because their opinion completely ignores the technical facts. No developer would ever bother with lightmaps and co again if we all had enough power for RT in all games. RT or derivates thereof like Voxel-GI / Lumen will become the standard for anything that is within our power limit, simply because it is by far the best solution.
Well you just hit the nail on the head, "enough power" currently we don't have that in the console space. Metro Exodus has RTGI and has very low resolution and the image quality suffers. You Sir have your blinkers on and you're coming across very passive aggressive.

Each developer makes their own decisions on what graphics features to prioritise. If what you are saying is correct then they must all be "idiots" as well, correct? As I said earlier, calling fellow posters "idiots" is not the way to go as we have not reached a point in real time graphics where RTGI is possible in every game.
 

Armorian

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It's also very demanding on hardware, is it worth the tradeoff? The answer to that would change from game to game I would imagine. Certainly calling people idiots for a difference of opinion is not the way to go.

Tradeoff depends on what is implemented and how well, for example i can't imagine playing CP2077 without RT reflections and RT AO but RT shadows? This option can just gone from main menu and I wouldn't notice, it's not worth it.

Need is a strong word. I just want to play videogames, bro…

So what are you doing in this thread?
 
Jan 3, 2021
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low res? sx pushes 1200-1512p 60 fps with full RT GI on metro exodus EE...

that's more than enough.

even ac valhalla runs at 1100-1200p 60 fps without any rt stuff . proves that ubisoft is trash compared to 4A games. or just look at doom eternal, it runs locked 120 fps on both consoles, and provides a 1440p+ 60 fps rt mode go figure!!

4a games and id software proved that 1440p 60 fps ray tracing is possible with these consoles. 4k was never a realistic target anyways... most games run 1440p 60 fps without RT. yet these two devs went ahead and pushed 1440p 60 rt on both consoles!

devs should learn to optimize their titles
 
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Shmunter

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Aug 25, 2018
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Let’s hope after all the resources go into real-time bounce lights, there is enough to create dynamic environments.

Played a bit of Metro on PS5, looks good….but I didn’t see anything dynamic environment wise thus far.
 

Haggard

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Each developer makes their own decisions on what graphics features to prioritise. If what you are saying is correct then they must all be "idiots" as well, correct? As I said earlier, calling fellow posters "idiots" is not the way to go as we have not reached a point in real time graphics where RTGI is possible in every game.
You`re putting developers which have to decide against RT due to power limitations and forum posters calling RT a "gimmick that will vanish again" in the same basket.....
The former are people who know exactly what they are missing out on and are probably crying in their blankets every night, dreaming about crooked lightmaps, and the latter are uneducated idiots.
 
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RoadHazard

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Haven't watched the video yet, but it's obvious that GI is incredibly useful in any game that has dynamic environments, time of day, etc. Anything where the lighting can change in real time. But if you're making a game where the lighting in a certain scene will always be the same (like an Uncharted or whatever), that processing can be done offline and baked into the game with as good (possibly better) results, and those resources used for other things instead.
 
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