Do Video Games Fake Buoyancy? 

Get a free 30 day trial and 20% off an annual plan at brilliant.org/acerola ! #ad Simple topic today thanks friends happy new year

I'm actually really glad the cat gag hasn't been removed because I find it genuinely fun to watch your cat

My favorite fake bouyancy is in the original half life. All they did was put a trigger plane slightly under the surface of the water, every time an object touches the plane it just kinda punches the object up a little bit And that's all it does

NO BATHS, NO MATHS

"Did Archimedes ever take another bath?" Actually yes, IIRC there were historical records uncovered in 2011 stating that he once bathed in blood inside Heavy's ventral cavity

I have one question - is there any correlation between buoyancy of the objects and successfulness of their distant relationships? Having trouble with my drowning simulation

The funny PNG computing man is back! My day has improved drastically

for the last problem, maybe you can list the incoming noisy planes in a cyclic buffer, and weight each plane by the distance from the newest entry in the cyclic buffer. You sum over all elements in the buffer and get an average plane, this plane is the target plane for each frame. Since we are continuously adding new planes to the buffer and removing the one with the smallest weight, the changes over time will probably be way smoother. Another thing one could do is to instead of snapping the orientation of the buoy, you could interpolate between current and target orientation.

Working on a buoyancy sim for my own ocean.. watching you go through the same thought processes as me was funny. To address the issues with the voxel approach (no control/ bad performance) i did a couple things instead of a plane fitting algorithm - Based the rotation of the object, if it aligned orthogonally with the oceans suface such that the cubes could same from ones "below" them, i could drastically cut down on the # of samples especially for ships which almost always maintain a similar equilibrium -To address control, i worked the buoyancy equation backwards to calculate the water density based on a desired height for the object to be at equilibrium for. This meant that for ships, all I had to do was set a specific y value to be the waterline and the program made it float there no matter what. It also meant the water density was different for each object, but that didn't have any effect so long as there weren't things that were Massively overweight and floating I have some questions about the gpu read back: What if you calculated, on the gpu, the lower frequency waves slightly ahead in the future such that when the packets arrived, they would be right on time instead of lagging behind (this would also help with noise). I'm not sure if its practical but I just thought of it now

Great video! I had to create a relatively convincing buoyancy sim at work for VR interactable objects. You did a fantastic job with this break down! The difficulty I found, most of all, was creating an interface for designers to end up implementing the parameters, per object, to determine physical values. Lots of fun! Designers have such high standards but then want simple controls!

Uh, thinking about the pressure on the surface of the object is actually way more applicable to how 3D objects in game engines are usually implemented. This can be done by using a displacement mesh, cutting it at the water surface and then calculating the pressure and area for each triangle to get the forces. Implementing things like slamming forces and surface friction also becomes possible. There is a great article by Jacques Kerner about the Just Cause 3 boat physics on the gamedeveloper website and a person called Habrador also has a Unity implementation with sample code based on it.

One thing that could also work is having the gpu return a grid of water normals around the origin of the buoy to the cpu where you calculate the difference in normals over time and apply that to the buoy. That way the cpu is interpolating the data in order to calculate while waiting on the gpu, so the buoys are always animating.

I kept thinking, wouldn't it be better to ask for the data in bulk? The time to make lots of little requests scales way faster than making few big requests. This is due to the individual overhead attached to each request. (Now imagine instead of talking to the GPU, you're sending data over the internet. Had to tackle that in my job.) Probably just shoving the heightmap into a render texture and reading that.

Since you mentioned the signal domain, the "noise" can be filtered with a simple damping filter (also known as Exponential Moving Average Infinite Impulse Response filter): o = lerp(i, o, t). This effectively removes high frequencies from your signal, simulating inertia and mass. Of course, you don't have to stop to just one filter (1st order), you can have up to 3 filters chained one after another for an even smoother frequency cutoff.

Your thumbnail made me realize where the word buoy comes from, so thanks for that random little insight :) (seems kinda obvious in hindsight, but then again I suppose most things do)

My first idea would be to sample the 4 corners, use a plane approximation, and filter that using a moving average window.

Amazing video. Love your content.

Isn't it possible to just stream a downscaled height texture of the water back to the CPU? That should be much faster than individual reads for each object. Also you can set a spring constraint in many physics engines, even the one unity uses. If you add an X/Z (or X/Y) lock to the body, you end up with a buoy that doesn't move and doesn't topple over (artist control) while still being physics based.

One thing I think could quite improve the simulation is drag. Objects in water experience significant drag which slows them down (tried running through a pool? Impossible). Moving objects, like ships, rely on there being far more drag sideways than forward/back in order to be able to turn properly. I made a game in 3rd year in high school where I implemented water simulation. The boats I used would sink noticably when jumping into the water, and would slide across when turned. Adding drag (high drag sideways, very high vertically) mostly fixed the issue. I don't remember much from his previous water sim video, but if the simulation isn't incredibly compute heavy, you can in fact just simulate it on the CPU for every point you need. I sampled 7 points on a boat's hull in order to determine the buoyancy.

i remember doing this myself and following a bunch of tutorials and what we ended up doing is getting the bounding box and then at the 4 corners of the intersecting plane with the water use spring physics to pull the current “plane” into alignment. i by no means came up with his myself but it’s a neat solution that gave really nice results, especially since we had a full copy of the water shader living on the cpu and could then use this copy to interact with the rest of the cpu things

I like the part in the intro where it's just a color background with texts, reminds me of monogatari series, so nostalgic ahhh😊

Great video. Presenting vastly different solutions is very important, if you need to decide which solution fits your project the best with a limited time budget. Thank you for providing this to everybody, Acerola. The voxel solution looked very promissing here. It could be something that might become feasible in future games. Almost then years ago I worked on a game with a large body of water and wrote a full height field sim on the GPU and a per-sample sim on the CPU. They were deterministic and ran synchronised and used artist-controlled wave patterns to improve control over visuals and gameplay. It was similar to sum of sinuses, it makes several things simpler, but less realistic, as was pointed out in this and an earlier video. You could perform multiple thousands of CPU side "samples" (they were pattern samples and computations instead of actual samples of a map, the height field did not exist as such on the CPU side) within a reasonable budget (a single / few ms out of 33 / 16 ms per frame) on then-current consoles (with very weak tablet-level CPUs), of which we only used a small fraction in the final game (probably low hundreds, it never came up in the profiler, so I don't know). To reduce the CPU side overhead, you could bundle multiple samples that were then computed in one go. That yielded some meaningful savings for scenarios like the one in the video. The approach in that game was otherwise quite similar to the last solution. I was a little worried for a while, that I had missed an obvious better solution. 😅 Seriously, there is always something new to learn in these videos, even if you've already got some experience in the topic. PS: This is one of a few select channels where I don't mind the in-video ads. I usually don't skip them anyway, but with these channels, I genuinely enjoy the presentation, as weird as that might be.

I think you might be able to optimize considerably the voxel technique by using different shapes. With that buoy example, 4 or 5 well positioned voxels might be sufficient to do both the height and the tilt, with one in the center and the rest in corners...

Fantastic video as always! We need more of what you have to offer! Your work researching, explaining, and covering topics without just talking about what your code does and showing code allows us to learn to code it on our own in our own ways. Keep this up! I'll for sure be subscribing to your Patreon!

Yo Ace I’m loving binging your whole channel as I learn blender

Love that you named your cat Brilliant, and that they sponsored this video 💕

I don’t know what it is about the way you make videos but don’t stop, your videos feel so casual while still being informative and it’s great.

I'd love to see you take on some rudimentary water interaction physics pretty similar to how RDR2 detailed theirs in the GDC paper. I think that would be an extremely interesting thing to add to your ocean simulation. Plus it'll help as you add more objects to the world

an acerola video a month keeps one feeling comf

Great video. You have one of the best and most informative channels on the internet! Love to watch your stuff!

My immediate thought in regards to the lag is that since it, gameplay-wise, doesn't matter what time the ocean simulation is at, if you could hold back the clock for the rendering time, you could have the wave visual sync up with the values you got from the gpu->cpu reads. I'm too lazy to go back to the previous vid to chek how the sim was stored, but given it's not just a simple function of time like a sum of sines would be, I suppose this might require a circular history buffer of wave maps or something

A physics video starting with a monogatari reference? What kind of dreamscape did i just stumble upon

TBH buoyancy feels so unpredictable IRL because of all inertia that I can imagine that this spring physics with some tuning will give believable effect. The fact that delay didn't affect subjective feeling only shows how much one can cheat on this.

Happy new year Acerola! Great vid as always)

Acerola must’ve tried a long distance relationship that went bad. Cause that was very accurate

Dude your videos are so good. Your timing between images is impeccable

i love your vids SO MUCH! thanks, Acerola.

Ayy new Acerola video! Happy New Year

At 16:00 I would recommend a dashpot/damper rather than a spring, I don't wanna overexplain if you know what it is, but basically instead of resisting based off distance like a spring, it resist motion from its current point, this prevents it from being pulled to the normal and instead allows it to drift around without being erratic

I love this video because the topic is one of the most obvious things that regular game players haven’t ever thought about. How I went my entire life without questioning how they make things float in games is wild

what a nice way to end the year with another acerola graphics adventures

Happy New year bro love your Christmas special

15:40 If you measure and plot the normal vector angle fluctuations, and then tune the spring and damping constant so that the angular spring has a similar resonant frequency, the motion won't be quite as smoothed out. Alternatively, if you all you want is to keep the buoy upright, you could apply a similar angular spring to the physics-based system. That way you could keep the nice angular displacements, while having a tunable parameter that keeps it mostly upright.

It would be interesting to see how the amount of voxels, (and maybe their shapes & distribution in the cube) changes the simulation. Great video as always !

I learned something new, the video is enjoyable, and there is variety of options presented! 🎉 10/10 video

You say bad game design, but I think it's perfect. I want large waters to be anti-player boarders in my dream game. Having rough seas that actively move the player is perfect! I want a 99% game over, but with a real possibility of survival. Like an irl rip tide. They don't automatically kill you, miracles can happen, but you're probably dead.

I always get such a happy feeling of excitement when this dude uploads I love the silly and random cool and interesting programming videos, it's so fun!

Very nice. I imagine that if the object wasn't interactive you could simulate it all in a shader.

Why did acerola have to go so far with the longterm situationship? Definitely hit a bit too close to home for me😂

Incredible. This is inspiring and really well done. As an audio guy looking to begin game dev, I wish there was a channel just like yours but for us audio nerds… but as you know in the industry, who gets their data compressed and cut first? Audio 🤣 thanks a million for the inspiration!

that's so cool, acerola. happy new year. edit: i just watched an entire ad read because cat videos were playing off on the side. genius?

16:00 so my suggestion is to use a first order lowpass filter here (there's some similarity between ideal springs and lowpass filters), each frame setting the value to partway between the last value and the updated value. any changes too far above the filter's cutoff will be reduced and that smooths it out. it can completely remove changes if they happen too fast, so sometimes it requires scaling up the input or output to compensate, but a higher order filter could more easily allow changes you want while still smoothing it out. a higher order filter could have a higher Q and rock back and forth faster when the frequency is just right, as often happens. there's possibly some overlap between this and what you were doing but hopefully it gives you some ideas to explore.

a monogatari and persona 3 ref in first few seconds, you have my sub

Hey, i made something similar a year ago. I was inspired by a part of the sea of thieves documentation, were they talked about having a complex visual ocean (gerstener waves) based on a more simple combination of sine waves. So my solution was having a nice looking shader(back then only shdergraph, bc i just started on cg) and calculating the the hight of the water with the biggest waves represented as sine waves. it looked nice and was really easy on the pc(my plan is to redo that stuff at somepoint and make the vr sailing expierience or puking simulator).

I think adding a little blip noise when notes/corrections are put on screen would be helpful because I'm a listener not a watcher and wouldn't know what I heard was incorrect unless I saw the screen.

Another banger! Man I like this channel!

Me, small brain: *Lerp it for smoothness*

For the more realistic simulation a thing that came to mind that would give quite a bit of artistic control and shouldn't be that much heavier to compute, just have a buoyancy multiplier for the voxels/areas and then you can easily make different parts of the object more or less buoyant. With that just making the top more or the bottom less buoyant should make the buoy auto correct unless it's completely inverted.

Beautifull! I loved the plot twist with reading data back from the GPU!, and seeing you go through a similar thinking process for bouyancy,, even though, i never went with the voxel approach for performance concerns, i did, stategically placed a number of "buoyant detectors" arround what i decided would be the bouyancy line of a given boat model,, theese detectoirs simply read a few data points for our ocean, and apply the bouyant force at a rigidbody at each detector location., if they are below the ocean water., they push up, and if not they fall, by gravity, wich ensures that the rotation of the bouyant object will match the waves outline arrount it, although that push up or down is running in cpu, is constantly in motion riding them with no lag. I love to see you took the simulation approach! Amazing!!

Awesome video man, really interesting project and great script!

there was no need for the long distance relationship gag because that literally happened to me and now I'm crying great video tho

My favorite math daddy

cant wait to see you fully simulate the wind forces and buoyancy of a pirate ship having the sails and rudder actually work

But Acerola?? How do you make these informative and entertaining videos about an obscure topic that is very hard hard to learn?? On a serious note your channel just became my favorite, thanks for all the hard work!

That intro of flashing text reminds me of monogatari

This was my final project for my computer animation class in my last semester of college

An interesting idea is to just combine them both! Have the cheaper method applied on buoys far away, where accuracy is not the greatest concern, and then when the buoys enter a close range of the player, switch it to physics mode.

i like how this video has floated to the top of my youtube suggestions. I hope it has the staying power to remain afloat and garner many views!

you are such a legend, i love your videos

great video, great explanations 10/10

Very entertaining. It seems that this is a case where the delay is not only helpful, but you want more of it. Because water is compressible, objects (especially heavy objects) don't react immediately to changes in height or direction. Thus you could send some portion of the changes into an "accumulator" that would release an average of the changes. I did this with a flight sim where I wanted to add a little lag into the time between inputs and results - to reflect that controls wires stretch and contract (like springs) and air is compressible. It worked like a charm. That might just be the tweak that you need.

You could set a linear interval to sample the gpu requests to smooth out the raw data coming in. That could be a "sample rate" variable that you can set wherein a higher sample rate is more accurate but has more noise, whereas lower sample rates result in less accurate but smoother motion. You could also simply bake the motion if the object is static. Since the sin waves won't change at that exact position after a each cycle.

It’s a bad game if the developers don’t take into consideration Quantum Entanglement.

0:47 why does this remind me of “speedy thing goes in speedy thing goes out” 💀

"Fake it till you make it." -Video Games

Great video as always. Wish I had more time to try it myself.

I just want to say Acerola’s cat + advertisement segment is the smartest thing ever.

It amazes me how similar is sound/music field to video game/grogramming. All these algorythms pretty much work the same but with different data. It makes me optimistic that if i understand one i'll eventually undarstand another.

Watching your videos with the sound off is like solving a rebus puzzle

a nice relaxing Acerola video (I'm shaking and out of breath from grinding out AC6's NG++ final boss (I was so damn close last time))

You need to set your center of mass on the buoy to be lower to automatically correctly avoid the stuck on its side problem and apply the force at the voxel position not at center of mass. It will then naturally want to tip to an upright position.

One idea is to do a bit of time smoothing so that the CPU snapshot has less intermittent effects. Sure, it'd make there be more latency between the water movement and the buoy movement, and you'd have to draw the water to a texture to do the time smoothing on the GPU side, but maybe it'd make up for it with the buoy being less noisy

yay new years graphics vid! Wonderful!! Thank you!

I feel like doing as many FFT computations as there are voxels in the object to get the water height only at that point might not be too expensive to do on the CPU, as long as the grid is sort of coarse.

3:50 was not expecting that to hit way that close to home for me. reopened some wounds there

Super interesting. Nice job man!

You can cut your simplified cylinder with the water plane and find volume and center of mass of the submerged part. That gives you a bouyancy vector. You can do a series expansion on cpu to get the value in single point.

My solution to all denoising for movement is recency-weighted exponential falloff. position and orientation = (alpha * previous) + ((1.0 - alpha) * newest values). When alpha is 0 you get the jittery one. When alpha is low you get slow movement. Tune it low for turbulent waves and heavy objects. High for light weight plastics and flags.

Acerola uploads, we watch.

the monogatari editing is so peak

New acerola video!!

get avg height of water in the area that's being touched, then lerp the results. movement up and down + rotation can be controlled with a variable. this also gives you control over the "sim", it's not going to look the best but it's certainly good enough in most cases.

The final problem just looks like a PID tuning situation.

Feels like spring has "too tough" coefficient. It takes several guessing iterations to find a nice look. At least in cloth simulation from scratch it took for me.

For the voxel aproach you dont need the volume displacement for them. if we have a dence enough voxel field we can approximate the displacement by just sampling the waterhight.

RU-vid RELENTLESSLY recommended this video to me since its release. I have high expectations now

Inertia (physics) and interpolation (simulation) would lend themselves well together. You can also use bounding boxes, coordinate systems, etc, as a performance optimization. Also, coarse grids progressively being refined into more granular grids only in small areas... Dividing the water into "chunks", etc.

the long distance cpu and gpu relationship hit way too close to home and tells me that I'm still not really over my 7 year relationship... thank you for the happy new year video computer game png man

thanks for continuing to provide the good knowledge acerola

"It's at this point that our problem space moves from physics to signal processing, as all things do." this line goes insanely hard