Tech Focus: Global Illumination - What It Is, How Does It Work And Why Do We Need It?

Welcome to a brand new Tech Focus! In this video, delivered with early access to DF Supporter Program backers, Alex goes into depth of Global Illumination - or GI. What is it, how does it work, what are the implementations with rasterisation and ray tracing?
00:00 - Introduction
01:13 - Part I - Theory: "What is Global Illumination?"
04:33 - Part I - Theory: "How does ray tracing simulate lighting?"
06:45 - Part I - Theory: "How does rasterisation emulate lighting?"
10:42 - Part 2 - Technique: "Lightmaps"
17:14 - Part 2 - Technique: "Ambient Colour"
19:54 - Part 2 - Technique: "Image-based Lighting with Cubemaps"
27:30 - Part 3 - Technique: "Probe-based Indirect Lighting"
32:21 - Part 4 - Conclusion
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[@BIaziken2]

good video, very illuminating.

[@andrewpiltenko9432]

quite enlightening, isn't it?

[@andrewpiltenko9432]

shines some light on many details

[@andrewpiltenko9432]

it's nice to hear a good explanation from a bright person

[@andrewpiltenko9432]

it was definitely Alex's time to shine

[@wiskerfall4519]

Kill me

[@BlueisNotaWarmColour]

I love this stuff! You guys should do more series documenting the evolution of specific rendering techniques/attempts at certain kinds of effects, sorta like the H2O video John did a while back.

[@ZK-ff2ru]

1 month ago but the video came out 7 hours ago??

[@alexbandli]

@@ZK-ff2ru early access

[@BlueisNotaWarmColour]

@@ZK-ff2ru fear me mortal

[@NextgenPL]

Yes do more stuff like this!

[@CmdrKeene]

100% agree!

[@apictureoffunction]

One thing this channel has taught me is that a lot of technical terms about gaming are incredibly straightforward.

[@RayCharlizard]

Tech Focus is back baby!

[@notRuskia]

I used to be a student of the professor that invented SVOGI. Wild to think that it'd be implemented in video games through ray tracing just a few years later.

[@TheCrewExpendable]

It’s still wild to me that real-time ray tracing exists in my (younger) life time. I thought I would be ranting to my grandkids “back in my day we had rasterized lighting and we liked it! None of this ray-traced 5000 fps retina projected images y’all have! Kinds these days are soft.” “Mom! Grandpas ranting about having to walk up hill both ways in the snow to pay 2 times MSRP for a used 1080 Ti again.” “Calm down dad or you’ll spike your blood pressure again.”

[@sushimshah2896]

Yeah I really hoped he at least mentioned SVOGI, in fact I commented that I hope to see it even before watching the video

[@mhannola]

This is one of those videos I could watch many times over and always learn something. So much great information packed into this. Great work!

[@EposVox]

Fantastic breakdown.

[@NubbinzGaming]

how is your reply one month ago when the video just came out? also love the quality you DF and harris heller bring to the platform. keep it up!

[@pastormolez8235]

@@NubbinzGaming Early access

[@gurkiratsingh8747]

@@mikeuk666 Wouldn't really call the second part as some sort of a win and actually unncessary to even mention that.

[@Taijifufu]

@@gurkiratsingh8747 It's ok, you'll get to say First on the next one.

[@Bossix84]

@@Taijifufu :D

[@E_Sunbro]

Alex knows his shit. Great video as always!

[@thewirv]

Nice, Remember Me, what a deep cut

[@soumyajitdeb3943]

Remember Me was also one of the first games (maybe the first?) to have a fully PBR pipeline. Still looks spectacular to this day.

[@x0b34rd4]

@@soumyajitdeb3943 what is PBR? Probe-Based Reflections?

[@soumyajitdeb3943]

@@x0b34rd4 Physically based rendering

[@Nolasco.]

Thank you Alex, i am a layman in terms of technology so this was really interesting for me and easy to understand. Thanks homie 💕

[@PotentChr0nic]

Yea can't believe how easy it was to follow! Would've loved to have an explanation for svogi as well but maybe next time

[@blanchbacker]

Global illumination is the most important part of modern game graphics in my opinion. Such a drastic change for people that can recognize fake/real lighting

[@Andrew-wb2zq]

Totally agree. It's the thing I'm most excited about regarding graphics technology.

[@SimonBuchanNz]

The problem is that we've gotten so good at avoiding the problematic situations for traditional techniques that you really need to know the tech to understand when something's impressive.

[@RoganGunn]

@@SimonBuchanNz Yeah devs have gotten so good at 'faking it' that normies often don't notice. Even for a nerd like me, sometimes the difference is so slight I'd choose rasterised over RT just to get the extra performance. Depends on the game though, of course. I guess it will save loads of dev time though, and like all new tech the devs need to learn how to use it to get it looking its best. Plus, we're in a transitionary stage right now... One day, real-time ray-traced GI and reflections will become standard, like pixel shaders and normal maps are today. Will need hefty GPUs though!

[@jcm2606]

We're only good at faking it in a very specific subset of games, typically games that can get away with baking most if not all of their lighting. In more dynamic games, many of the techniques that get close to full raytracing just aren't feasible due to the dynamic nature of the games, and so you're left with alternative techniques that just don't cut it, for one reason or another. GI especially is a hard one, because the only alternatives are generally slow (slower than even full raytracing, when you try to fit more geometry detail into them), and support a limited amount of bounces (1, 2 if you're lucky).

[@omgawesomeomg]

35 minute Tech Focus? Yes pleaaaase.

[@sadstormtrooper]

2:10 'Perfectly Dark', pops in a photo from Perfect Dark, hahaha, I love Alex's humour and his effort to insert such details

[@MediaBrad]

9:01 Pitch Black reference with Vin Diesel too

[@moosemaimer]

@@MediaBrad you don't need bounce lighting when you have _family_

[@Boodoo4You]

@@moosemaimer That whole “family” BS meme was cooked up by FF marketing department. They astroturfed Reddit hard with that shitty meme

[@alexsilva28]

@@Boodoo4You took a page from the Sonic movie I see

[@AndyGilleand]

Sonic Unleashed is one of my favorite examples of games that used baked GI but incorporated one of the first examples of light probes to generate a GI look in dynamic objects

[@cobiefullerton6015]

Alex and John make some of the most high quality videos on KZbin, those guys are nuts

[@SirCalalot]

Incredible work as always Alex! Even as an industry tech guy, I still learn so much from your videos. Keep being awesome! (Now to look into the viability of converting Turok PC over to a Path Tracer...)

[@dannonyogurt98]

10:22 who else has that StarCraft theme burned into their skull?

[@Xator]

This guy!!! ;-P

[@offspringfan89]

Terran Theme 1, my favourite!

[@gingersnaps6941]

Was looking for this comment.

[@ThomasTrala]

My exact thought! Glad I wasn't the only one!

[@thyroid99]

Now I have to find the track to get it out of my head lol

[@faustianblur1798]

I'm surprised there was no mention of SSGI, either the UE4 implementation found in Gears 5 and Days Gone or Pascal Gilcher's Reshade implementation. It's that missing link between ray tracing and rasterisation that perfectly demonstrates the limitations of the latter.

[@okaybutwhythough7456]

How does it perfectly demonstrate the limitations of rasterization? RTGI itself is already a perfect example of that and SSGI is just a downgraded version of that, and thus doesn't show the difference as much. It's still a pretty nice thing to have and is a decent solution to add on top of existing lighting if full RTGI is too demanding.

[@faustianblur1798]

@@okaybutwhythough7456 SSGI is a post process and can only work on the limited information available in the framebuffer. It exhibits artefacts due to missing information from surfaces being off-screen or occluded causing the indirect lighting it produces to change radically as different pixels become visible, even from relatively small camera movements. It's really a very poor and unstable approximation of GI compared to any other method.

[@okaybutwhythough7456]

@@faustianblur1798 Then what were you on about talking about how it perfectly demonstrated the limitations of rasterization?

[@faustianblur1798]

@@okaybutwhythough7456 rasterisation works by sampling the scene at each visible pixel on each visible triangle. At the time of shading it doesn't know anything about any other points on any other surfaces, let alone how much light they might be reflecting toward it. To approximate GI you therefore have to sample back a pre-lit representation of the scene passed to the shader. SSGI makes a good example of this limitation because it traces/marches rays through a representation of the scene, similar to RTGI, but is limited by that representation having been rendered into a 2D image (with depth information). It's that lost information about the scene that is the key difference between rasterisation and ray tracing.

[@okaybutwhythough7456]

@@faustianblur1798 Yes but at that point just using full on RTGI as an example works better than SSGI.

[@griffgames9538]

Lighting is the crucial baseline for human vision to perceive color, dimension, and depth. One of the reasons we're easily impressed by viewing a game scene with plenty of realistically arranged well-baked lightmaps, despite being static diffused lighting. Or why more stylized art direction like R&C Rift Apart can still feel incredibly sophisticated and immersive - our minds can suspend disbelief of the stylized presentation, yet still be dazzled by impressive lighting and ray-traced surfaces, as it communicates significant information and 'sense of place and time' to human perception of our surroundings.

[@dustblowingman]

Yay been looking forward to this since it was announced

[@AndyGilleand]

I can't wait until the day when RTX will have so many rays possible that we'll be able to do the same kind of full scale path tracing that is even rare in CGI movies today due to how time consuming it is.

[@unfa00]

I am not sure it'll be an optimal use of resources, because a lot of the lighting can be "faked" pretty well with rasterization-based techniques. Having *fully* realtime global illumination (not just indirect lighting) is very exciting, but it could also be distracting in games and make it harder to play. Quake 2 RTX has some of that, where the lighting becomes too dynamic and the game world can go from pitch black to blindingly bright very quickly during frantic fights in tight spaces and it can have adverse effects on the gameplay IMO. Modern games use raytracing mostly to augment the rasterized image, not to replace it completely as that'd be unfeasible but also needlessly expansive even if possible - as Quake 2 RTX demonstrates IMO. I guess it is possible that the raytracing techniques and hardware will improve with time bringing both manufacturing and running cost down to the point where it becomes feasible to make raytracing-only games, and dropping a traditional rasterized lighting as a fallback. It'd be interesting to see what game designs could emerge from that, especially when the indie scene gets their hands on this technology.

[@AndyGilleand]

@@unfa00 my point was that eventually, there will be no reason for those shortcuts, the power will be so good that it would be a waste not to go full multi bounce GI pathtracing all the time.

[@Secret_Takodachi]

Man... imagine still being optimistic for a "better future" 😂 it's a race to the bottom dude IDK if you've been paying attention but success isn't achieved by those who work the hardest or push their medium to its limits. Success in 2023 comes from exploiting existing intellectual property for the lowest possible cost & selling that hackjob product to the massive audience of frachise fans (who have no standards or reservations about buy & playing a badly made game that's based on their favorite IP) LOL, wait... did you actually think anyone involved at the leadership level actually cares about making good games? Dude, almost all of those people retired/left the industry years ago. It's all about licensing existing assets & crunching disposable workers to make those licensed assets into a facsimile of a "game" with a "story" 🤣 "Imagine how good future games will look..." No. I don't think I will engage in this pointless thought experiment.

[@AndyGilleand]

@@Secret_TakodachiNone of that is true.

[@StrazdasLT]

@@unfa00 Light baking is very resource and developement time intensive and will go away and be replaced by ray tracing as soon as the average gamer has hardware powerful enough to run that at normal framerate.

[@cosmic_gate476]

17:33 is literally what Venus looks like, due to the dense clouds and no bounced lighting from nearby objects.

[@granatengeorg]

Coming from an environment artist working in dem vidjagaems, I just want to let you know how much I appreciate the research and attention to detail that you clearly put into the video. Great job!

[@sushimshah2896]

We (I know it's a small %) certainly respect & appreciate all the work & attention to details game devs put into games. And I obviously like watching videos like these as well which point out such details

[@abdmo7575]

very underrated video unfortunately i hope youll have more time to make more 'tech focus' videos in the future

[@nbafrank]

This is so detailed yet very accessible. Perfect technical communication.

[@Grammostola]

Probably the best "why Raytracing is so important"-video I´ve seen so far.

[@mattdhargett]

Great shoutout to Remember Me!

[@strgazer24]

This type of content is why we all love df

[@gangstarxxl]

The Outro Song was amazing ahahaha

[@glinteastwood]

This is so elegantly laid out. Fantastic work!

[@Mastersaifer]

This is incredible work, Alex. I need to watch it like three more times to retain it all, but if I was a teacher I would proudly show this to my class. Well done!

[@resonatingraptorid6519]

Thank you for shedding light on this

[@OroborOSX11]

I absolutely love this. Would love even more detailed breakdowns of complex topics in lighting, materials (PBR in particular), evolutions in modeling, etc. Great work!

[@Depi115]

Fantastic, thanks for this, was waiting for a new tech focus. Would be much appreciated if you did them more often.

[@jaytb6458]

I'm always looking forward to videos like these. Keep up the great work!

[@TheCanadian0495]

So happy to see Tech Focus coming back. Tremendous video as always!

[@DGFTardin]

I was missing Alex, great to have him back

[@pillington1338]

One small correction, many games with only direct lighting don’t have pitch black shadows (unless we’re counting ambient light color). Shadow stencils in Doom 3 have that effect but shadow mapping is a second pass and the shadows generated there are overlaid on top of a color pass that’s already been made, and the devs get to decide how transparent those shadows are. Shadow mapping still uses only direct lighting though.

[@sheldonpetrie3706]

You don't need rasterization when you've got Family. I will always appreciated an excellent Pitch Black reference.

[@F7GOS]

Love a Cheeky Tech Focus Video - especially when it is so clear, concise and entertaining.

[@joey199412]

Amazing video, this helped me understand lighting in game development more.

[@goonerlee]

Thank you Alex and the rest of the team. I have learnt so much from you guys in the last couple of years.

[@GTD_Galatea]

I feel enlightened after watching this video. Please make more videos focused on the tech behind the games we play in the future.

[@Jprime777]

Great video, this shone some light on the topic. I feel brighter already.

[@gurkiratsingh8747]

0:50 I remember this, Remember Me

[@ramyabouhassan]

YEAH Ive been save from boredom now with this video i can distract myself for a while, thanks for such deepdives love the content and detail as always

[@Sperry21322]

I feel like I am back in school and loving it!

[@theusual5uspect]

I really enjoyed this. I’d highly recommend using Cycles and Eevee in Blender to showcase these effects, would really allow precise demonstration that some of the diagrams can’t easily convey. Especially things like screen space effects which were glossed over a bit.

[@TheSliderW]

isn't screen space basically cube mapping ? Edit, oh, no I was thinking about something else. Yes, screen space reflections are an entire different thing using a specific screen buffer to provide the colour data to other objects in the scene but mostly for reflections.

[@theusual5uspect]

@@TheSliderW no, it’s basically in a very basic sense copy pasting what’s on the screen, that’s why the trees disappear when you look down at the water in a game like far cry. A cube map isn’t limited by screen space.

[@ReneHoffmann194]

Well explained. I love this type of content. Thanks a lot.

[@Paddydapro]

Holy shit, this is one of the best videos you guys have done, also special thanks to Alex for his in depth presentation it really seemed like a single take :o Auf Wiedersehn!

[@DTKblaster]

This was fantastic! I'd love to see a similar Tech focus episode looking at the evolution of shaders and the hardware they run on, from pre DX9c fixed function HW with non-programable shaders, through the DX10 era with the G80/HD series cards up to modern DX12 stuff :)

[@dustarma]

I wish you had showed some examples from Sonic Unleashed, given just how high quality its prebaked and dynamic lighting was for a 2008 game.

[@oneandonlyjark]

Back in my day, we learned this as: specular + ambient + diffuse lighting sources

[@bloodlustuponme]

10:21 That StarCraft/Brood War music brings back memories. *injects Stim pack*

[@chumpwhizii]

DF is knocking it out of the park as of late, great work all.

[@Schraiber]

I just started the video and I'm already so excited

[@vesselinkrastev]

Outstanding work! Very informative. I love Alex's tech focus videos!

[@samza9622]

It's the most taxing ray tracing effect it's crazy that metro exodus has it on console especially being 60fps and the resolution it's at.

[@samcs06]

Really hope other developers see that it's possible and try to use the same approach

[@guspaz]

We'll eventually see all games migrate to it as sufficient raytracing performance is available on lower and lower end cards and as the market share of non-raytracing cards shrinks. Sort of like how Doom 3 more or less sounded the death knell of DX7-class cards (though the popularity of the GF2-in-disguise GF4 MX required an exception). Metro Exodus might be the first game to require it (though that's actually debatable since the "non-enhanced" edition exists as the fallback), but there will be more, at an increasing rate, until all games do.

[@sushimshah2896]

Isn't RT reflections more taxing?

[@theninjamaster67]

@@sushimshah2896 Technically yes but there are games with 60fps ray traced modes on console you just gotta make some smart optimizations to make it possible.

[@sergeysiminyuk]

@@theninjamaster67 consoles most likely will see RTGI along with reflections and shadows in at least 3-4 years when RT techniques evolve enough to run on the weaker RT hardware. Granted the Xbox has the potential to do it earlier if DirectML delivers something close to DLSS.

[@Daniel-yz3zf]

I think these are very important videos in the context of this channel. I think you guys overestimate the amount of people that actually understand what you talk about in your videos! I genuinely believe a large majority of your viewers are very casual with not much deep technical knowledge, who may not even understand any of the terms or techniques you discuss... so these videos are important ways to bring those viewers in even more.

[@TheSliderW]

Oh wow, I wasn't expecting you to dive so deep into the subject. That was much more informative than expected. Great work !!

[@IRDean]

Really enjoyed the video. It is clear a lot of time and research went into it. Kudos!

[@fabrigarciacartoons]

This is one more reason why DF are the true lords of knowledge

[@carlosnascimento9269]

This is excellent work, Alex. Congrats.

[@taylorrajaniemi8678]

Would love to see more videos like this from the channel - very informative and approachable. Love the examples given, really showcased the points. Thanks for all the hard work!

[@CesconetoG]

One of the best Digital Foundry videos ever! Please do one more talking about the other techniques!

[@jdgonzo1982]

that was awesome...and what an outro!! :) thanks Alex!!

[@PenguinYayOne]

Finally some good tech material. Go DF!

[@mookid2223]

I love these videos, so much detailed information for so many different techniques, super interesting stuff.

[@MelissaAtwell]

Thank you for this informative video, Alex!

[@georgelopez9411]

Amazing. Would love a "Lumen vs Real-time raytracing" tech focus

[@okaybutwhythough7456]

Lumen is not as precise but runs a lot better and doesn't require hardware acceleration. Pretty much sums it up. It just uses and combines several different forms of tracing instead of triangle tracing like RTGI.

[@MrBurtbackerack]

Love these videos not just for the content itself but the comment section is usually more chill with the more tech nerd types coming out and the gaming fanboys mostly gone.

[@Yura-Sensei]

your favorite game sux balls

[@wmka]

Watched til the end. Wasn't disappointed. Thank you and have a good one.

[@Demmrir]

Know what'd be really fun to see? A ray-traced Doom 3. Substantially better quality models than Quake 2 with actual bumpmaps and such, but also it's a game with the harshest direct lighting in existence and global illumination would fix one of two primary complaints with the game (how goddamn black it is).

[@cosmic_gate476]

The other thing is the movespeed and mechanics, which I doubt would change lol

[@concinnus]

Since Doom 2016 was a reboot, this seems unlikely. Maybe a prequel with a Doom 3 level design would work though.

[@TonkarzOfSolSystem]

The game isn't designed for less blackness. It would be an interesting tech demo but as a game it would only be fun by chance.

[@tiarkrezar]

It'd easily be the most impressive way to show off what global illumination can do, especially as it was designed to have many moving light sources. Most other games since the late 90s at least attempted to approximate GI in some way, while Doom 3 just went "lolno, pitch-black ambient is all you get"

[@Whisper117s]

I understand the appeal but as TonkarzOfSolSystem said, the game would completely break as it'd lose its main feature: being afraid of what can come out of...pitch darkness. What could be interesting tho is raytraced shadows to get rid of those horrible shadow edges !

[@GalZemach]

This was really great! I learned a lot, thanks!!

[@Draggobuttboi]

Pretty soon we'll finally get fluid simulation, only 10 years late!

[@Lordbugbug]

do you think if we got fluid sim, we'd also be able to achieve accurate smoke sim?

[@bladerj]

we had fluid simulation for years, they just dont implement on games because it is too taxative on consoles cpu, now smoke simulation is something im more interested.

[@jashpaper8370]

With ML it might be possible within a year or two

[@concinnus]

As soon as AMD adds ML hardware to their GPUs.

[@Lordbugbug]

@@concinnus whats ml

[@AlexFromTheDistance]

Bravo! Great educational content! Please continue.

[@TilSkywalker]

So glad the bespoke Tech focus videos are back!

[@alexsilva28]

That was really informative and explained a ton of things I noticed from years of playing games but never bothered to research or try to understand. Fantastic video

[@SteamPunk96]

It's videos like this and DF Retro that make me want to support you guys on Patreon, I can't right now but I will... someday! Fantastic as always, Alex.

[@symol30872]

Great video as always. I love these technical discussions

[@GhostofCam]

This video is superbly executed. Well done !

[@meshumi1]

Fantastic breakdown. Thanks for this.

[@Tactic3d]

wow! What a great video! It's detailed, well explained, and required a lot of work. Respect.

[@rx1834]

A brilliant essay, very well-done. And it's an important one to watch to fully understand DF videos and the technology they talk about.

[@kelownatechkid]

Alex is back! Awesome video!

[@ShadyFurball1]

Excellent work. First time seeing Alex without his headphones I think.

[@CowCatwithafancyHat]

This took a lot of work, Thank you!

[@MangoBS]

I really enjoy the tech focus videos. Please continue to make many more.

[@BeatCrazey]

Lovely video! Those diagrams perfectly illustrate what each technique does. I remember learning a lot about them when mapping for both the Source 1 and Source 2 engines...

[@Navhkrin]

It was a bit ambiguous to explain fill color after light maps even though fill color is the oldest technique in the list (predating even the direct illumination) but very well made video! Fill color is basically act drawing things as they are without any lightning calculations.

[@Boodoo4You]

Such incredible technology that we take for granted every day. Great video!

[@xen0bear]

Learned a lot from this. Fantastic video!

[@Vagabundo74]

This was an amazing video! This kind of content is definitely worth subscribing to.

[@harrygeoffrion4520]

Fantastic video Alex, thanks!

[@kemalatayev]

Brilliant as always!

[@St3althPaRad0x]

So much information. Thank you!

[@mikemuponda1781]

Thank you Alex, fantastic job!

[@e2rqey]

Oooohhhhh yeah. I've been waiting for this!!!!

[@Literal32]

Love the use of the Turok character model. Always a blast to see in your videos

[@robertcarr4172]

Excellent vid Alex!!