VFX Artist Explains the HARDEST Visual Effect to Make

visual effects can bring our wildest imaginations to life now more than ever in fact it almost feels like it's easy except recently i saw a shot that blew my mind [Music] no it's not the dino we've been able to do dinosaurs for like 30 years now no it was the water caustics on his back the way light concentrates into these patterns of light is something we actually see every single day but is actually one of the hardest things to do in all of cgi that's why in this video we're going to be diving deep into how caustics work and why everything is alive holy crap did i just nail it actually what is the definition of the word caustic definition says able to burn or corrode organic okay that can't possibly be it sarcastic in a scathing and bitter way i don't think that's also it that was stupid and a waste of time a caustic is essentially the concentrated patterns of light you get after the light passes through stuff like glass but you see them all the time and you probably don't even realize look at that costume oh what look at that costume right there [Music] there are lots of other examples in movies and shows throughout the years it makes for a very cool looking set caustics are a physical phenomenon which means that they can be simulated now simulation tools have gotten better faster and easier to use over time we can pretty much simulate most things you know we got smoke and fire we got liquid water simulations we got ragdoll physics rigid body dynamics however it's easy to forget the most common thing that artists simulate light because rendering engines literally simulate how light interacts with the environment in the world there's a bunch of different rendering engines out there and all of them handle light rendering a little bit differently [Music] the way light works in reality is pretty straightforward a light source emits photons that bounce around an environment before landing in your eyeballs or camera the brightness and color of these photons are directly changed by the materials they bounce off of so when they eventually land in your eyes they form an image rendering engines try to replicate this concept by tracing the paths of those photons but instead of measuring them from the light source to the camera they are usually traced in reverse from the camera back to the original light source if array makes it all the way to the light then you get the color and brightness information for any given pixel and this is called path tracing if the light simulation was not limited in this way then the computer would attempt to simulate the infinite number of light rays and bounces that propagate in reality which would literally take forever so if caustics are just a phenomenon of light then i should be able to render it right okay time to render some caustics let's do this i just made a simple little scene here got a donut got a cylinder got a little blobby sphere i have them coming out of the ground here look at this so i'm gonna see if i can get these to render caustics i've got it rendering out to 16 000 samples right now we're getting something we're getting something we're getting some gossips why is this taking forever a little longer than a few minutes later oh my god it's still nowhere close to finishing why is this taking forever i give up i don't get it why are caustics so hard to render costumes have been changed oh yeah this is jules erbach the founder and ceo of otoy which is responsible for octane render my favorite render engine hostics is an art form it's been something people avoided classics that they used to avoid you know skid there is a reason why classics are difficult and that's because you're you know when you're doing typical rendering if you think of light like water you're trying to catch a bucket of light and you cast a wide net and ultimately you get a result that's averaged out and it's maybe a little noisy but it worked if you're trying to render something like a laser or something for magnifying glass all that light think of it being sort of like put through a complex nozzle and all of a sudden those paths individually need to be traced you know that's where classics become really hard in order to just you know follow through the rules of physics and light if you do sample things you know caustics are the things that you need a lot more samples to get the actual result you just have to calculate a lot more individual photons versus just approximating an average of how light spreads throughout the scene and you know it's it's one of the more expensive parts of the red ring equation you know you could make it put a gobo right in front of a light and call back mustangs fake it with gobos okay great what's a gobo a gobo is a type of screen that you actually put in front of a spotlight to project a shaped shadow of something like say blinds or ferns or trees leaves that sort of thing and since that is something i can do practically i can replicate it digitally as well instead of using say ferns or blinds or whatever random shapes you have you can substitute any sort of black and white image in that you want or perhaps caustics and you can take that another step further by using an actual texture image sequence a video file you can literally record footage of the caustics at the bottom of a pool clamp it down into a black and white image that can now be our projected light shape it just happens to look like real caustics if you're to simulate that for real with an actual surface of water the light has to then bend the correct way and that takes so much longer to calculate it's the same exact principle of using a real gobo but it's so much cheaper to render this is generally the way it's done across the board in visual effects because doing it for real kind of just is not an option it takes too long so now i'm wondering if i can replicate that shot from prehistoric planet by using fake gobos if you remember the jurassic park video we did last fall we have a nice high quality 3d model of a t-rex and these are the results look at the patterns of light on the t-rex's back and how it actually falls off the same way it does in prehistoric planets i'm now convinced that this is exactly how they did it in prehistoric planet all of these caustics are probably the result of gobos but i'm not satisfied faking these caustics with gobos i want to do them for real and luckily there's a brand new render kernel called photon tracer it turns out that there's you know more sophisticated ways of rendering plastics and that's what the photon tracer does it's doing it in a way that gets you to the results that would take million times longer faster it is traditionally full-time mapping with path guiding all these things and you end up with something that solves all these problems no compromises full speed full quality it's not instantaneous i mean but it's really fast like a thousand times faster if you turn that off and you pitch to tap tracing it's not going to look any different if you let it go all the way to the same number of samples and that's the magic of it so now that i feel that i can actually correctly simulate caustics in a renderer i want to put them to the test by comparing them to what i can film in real life these are like the classic kinds of caustics and if you're using the sunlight something like this is actually strong enough to catch things on fire it starts getting oh my god it's already starting to burn fire fire fire this bee's already dead this this bee is already oh god oh god dude i want to have freaking spots in my eyes now don't ah ren dude you saw how quick that was you know that's hot i know it's hot but i just wanted to feel it if you have a vr headset this is exactly why you should not put it down with the lenses facing up because the sun will literally melt the screen so i got the idea to try to actually replicate moving the magnifying glass in real life so that i can replicate it digitally to see if the caustics match up to do so i'm literally going to use my phone as a motion capture device literally tracking the position and rotation of this magnifying glass here do the rendered caustics match the real caustics we'll find out here in a moment i wanted to take a quick break from all of this rendering talk to tell you about our sponsor squarespace you know what's nice about squarespace you don't have to know anything about making a website because they've got so many award-winning templates right for you right now if you're running a business it's imperative you know all of the analytics and data throughpoint through your website and guess what squarespace gives you all of that control and all of the data you could possibly want at your fingertips ready to go and if you want to take that a step further with multiple contributors you can have multiple different people contributing to your website all with different permissions set by you also i understand having to post across multiple different social media accounts well guess what you post your website it'll automatically post to all of your social media accounts all at once and i know what you might be thinking if squarespace is making my website do they own the website no everything you put out you own you know that for a fact if you got videos that you want to put on your website you can optimize the loading speeds of all of it by using their video block system to make sure that everything loads exactly when it's needed why do i do hand gestures i cannot talk without my hands anyway thanks again to squarespace for sponsoring the show they've been our sponsors for a very long time and i always appreciate the ogs in the sponsor space so if you want to start your own website whether it's for starting your own business or sharing your artwork head to squarespace.com corridor crew and you will get 10 off your first website or domain now for some caustics but here's the thing i can't replicate this magnifying glass unless i actually replicate the properties of the glass itself index of refraction dispersion these are things that i need to put into the material in order to actually get the same type of caustic and lo and behold i'm actually replicating the real caustics pretty accurately there's some small differences here probably because i didn't model the lens exactly the same but i mean this is pretty close especially when you see when i move the magnifying glass forward and back like that the way the light inverts that is pretty interesting the fact that i was able to replicate that for real man this has inspired me now that i know that caustics are literally as easy as hitting the check mark on the renderer it's like i kind of want to go crazy what sort of caustics can i make so i've become obsessed i have started rendering out a bunch of different examples just having fun with it it's super easy to set up caustics but there's still a problem caustics are still very slow to render this one shot right here took 100 hours to render at 720p it took 100 hours to render on a computer with a 30 90 in it that's a long time to render but think about it this way if i wasn't using this it would have taken 100 000 hours to render how long is that hey siri 100 000 hours in years 100 000 hours is 11.41 years i guess a hundred hours isn't that bad but i cannot stop thinking about that prehistoric planet shot like i feel like i can probably now actually simulate those caustics for real and that will give us an opportunity to directly compare the gobo caustics to the real physically simulated caustics and this might actually show us whether it's worth it to simulate those caustics for real now so check this out i've got x particles it's great and they have a super simple ocean surface thing technically this ocean surface is not simulated it's based off of a noise map but the light passing through it is simulated so i'm going to call this real i mean look at that it's real it's real i'm actually simulating real caustics on the back of a dinosaur i feel like i achieved something here now let's actually compare the results right away i think the first thing i noticed is that the fake caustics are a little too consistent if we ignore the scale here for a moment i think the simulated caustics have a slightly different off look at the intensity of the lights at the brightest points on each image notice how on the simulated caustics the light actually has this nice fall off it feels a little bit more natural compared to say the gobo where it's kind of just the same intensity everywhere but you know what the results are pretty similar like it's cool that these are physically simulated and it does technically look a little bit more real to me but is it worth it i'm not so sure especially when you're able to kick out like 100 more shots than you would be to simulate it for real so yeah it turns out there's not really too much difference between fake caustics and simulated caustics i mean yes the simulated ones are a little nicer in my eye it's just that the difference is so negligible it's not really even worth worrying about so much so in fact that we actually applied this principle in real life i literally took the exact same texture sequence i've been using to make all of these fake caustics but i put it in a real projector that we used to project caustics onto me for the opening shot of this video so that opening shot has real caustics fake caustics does it matter i keep using this term fake but think about it all visual effects all cgi it's all fake i mean think about reality you have an infinite number of light bounces going around a scene infinite number of substeps for all of the simulations you see around you all the textures are super high resolution everything is hdr and it all runs in real time without ever crashing visual effects it's all a trick none of it's real there's always some degree of craftsmanship that is creating something for us to live in for a brief moment in time to escape reality to suspend our disbelief and as long as the tricks we employ get us there it doesn't matter how we got there so now that you've made it to the end of this video and you've learned everything that i hope you've learned from this randomly super nerdy esoteric niche cgi video i want you to start considering the trailer of avatar 2. are the caustics in that movie faked like i've described or did wheta go beyond and above what is necessary by physically and accurately simulating how light works for a movie that takes place almost entirely underwater when you eventually get to check out this movie i want this to be on your mind are the caustics physically simulated if we can actually get wetter to make a statement about the caustics in the movie that would be even better that'd be so cool if you have any ideas for other sort of like randomly niche cgi things that i can maybe dive into and really get the whole picture about it let me know in a comment down below and maybe that'll be an upcoming video [Music] [Music] you

Channel: Corridor Crew

Views: 2,653,094

Keywords: vfx artist, react, reveals, shows you, explains, simulation, caustics, caustic, light, ray tracing, path tracing, octane, render, renderer, otoy, avatar 2, visual effects, cgi, learn, education

Id: 7l6QOcgWXfI

Length: 15min 38sec (938 seconds)

Published: Thu Jul 14 2022