How Do Games Render So Much Grass?

An overview of my grass rendering explorations and an implementation of billboard grass, a common technique used in nearly every single video game.
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Code: github.com/GarrettGunnell/Grass
References:
developer.nvidia.com/gpugems/...
Music:
Gold Falls Casino - HuniePop OST
Joy - Persona 3 OST
Bad Bully - Kizumonogatari 2 OST
Chapters:
00:00 Intro
01:36 Getting Started
03:37 GPU Instancing
06:51 Improving Appearance
10:07 Finishing Touches
11:50 Optimizations
14:04 Conclusion
Thanks for watching!
This video is dedicated to my friend, Alotryx.
also please subscribe haha please man please just subscribe dude please just like one sub I swear I'm not addicted please man please just one sub please
#acerola #gamedev #graphics #unity #indiegame #unity3d #madewithunity #indiedev #unity2d

[@spwwww8258]

Just wanted to address one point about using GPU Instancing: Without GPU Instancing mesh data isn't copied from the CPU to the GPU every frame. That's why the GPU has its own memory. The mesh data is loaded to the GPU once, only a small amount of data which tells the GPU how to render that mesh is updated constantly. For example data about where the mesh should be rendered. (uniforms) The performance problems thus don't stem from having to load too much data to the GPU, but by bad scheduling. When rendering each instance of an object separately, the GPU and CPU are constantly in a dialogue and have to wait for each other. With GPU Instancing the CPU combines all of that data, sends it to the GPU and then lets the GPU vroom vroom through the workload without any interruptions. Whats also nice is that with GPU Instancing you can just keep that data around on the GPU for as long as you like. So you have the flexibility of updating it every frame, only sometimes or only once. Updating a complete mesh every frame is sometimes referred to as streaming and only done in very specific circumstances. Constantly shapeshifting terrain maybe. Though even then other methods are usually preferred when possible.

[@ewinter9021]

Great explanation. Wanted to ask where did you learn about this topic? (A class or book perhaps? because as a wanna-be indie dev with no technical training i would love to begin researching things like this but it definitely doesn't seem like entry/gateway material and prob has tons of prerequisites to understanding lol). TLDR: How did you go about learning this information? And do you have any tips on resources that could be useful to learn or understand this in more depth for those getting started?

[@turkym7md5]

@@ewinter9021 You can fire up a c++ project and start tinkering with OpenGL, look for an opengl c++ series or a book it would teach you alot about GPUs

[@turkym7md5]

Another use case for updating a mesh every frame is for 2D batching, because every frame you have to resort and recalculate the batched sprites and send their mesh data to the GPU.

[@bash0985]

@@ewinter9021 There are also some good books and video series' using Java instead of C++ which might be a bit more friendly to people who haven't dealt with it before. I personally recommend ThinMatrix's 3D engine series on KZbin and the book "Computer graphics programming in OpenGL with Java". They teach graphics programming from the ground up and are much lower level and in depth than anything you might do in Unity

[@maximeumbra7235]

Pretty accurate description although the performance issues aren't "exactly" due to bad scheduling over which you get no control in the first place, big part is very poor bus performance with the number of commands sent but that isn't it alone either, on the GPU side large bottleneck also arises from warp under utilization when the commands are sent in a manner that don't use the full warp width, in addition say 10k commands to process isn't exactly a walk in the park within a common 5ms frame budget usually afforded for driving the rendering. The basic notion is damn good though and while the position data isnt necessarily uniform this does a good job to illustrate that if you have more than a dozen of anything you need to batch in one manner or another (method described here isn't the only one, you can also use constant buffers for direct pointers to the vert position buffers etc)

[@level7feeders13]

1970: people in 2020 will have flying cars 2021: in order to render grass you need grass

[@Rudxain]

This is why we need to touch grass

[@joewilliams8286]

Best video I’ve seen on the topic, love how you give detail over the whole process and explain the theory behind it… gained a subscriber

[@Acerola_t]

Thanks so much!

[@AlexTuduran]

You could randomize the y-axis rotation, randomly darken it with a very low frequency noise for more color variation, use material ambient occlusion to further improve the definition of the grass, use an atlas of grass textures for even more variation, implement basic specular reflection for a more pbr look and some basic sub-surface scattering. Regardless, this is a nice explanation.

[@HKragh]

Hi, fellow tech artist here: Overall nice look. I would add some additional effects. Grass should animate a little more in zones of related movements, and in waves. Then there is lighting. Calculate a standard fresnel effect (dot(pos-cam, viewDir) as uv in a fresnel LUT), and use the sky color as a tint where grass is seen very heads on. It will highlight the curves of the terrain. Also grass is a 3D structure in a vertical position, so calculating some light based on viewing direction (dot(pos-cam, lightDir)) would work wonders. As grass animates, it changes how it faces light, so could also do something here, to make it change lighting as it waves. Lastly: grass is shiny, so adding some soft specularity (again use the pos-camPos as a pseudo normal) is a nice final touch

[@ChoiceOfIllusion]

4:30 I don't think storing a huge buffer of positions on the GPU is by itself instancing. The way I understand it is if you have say a 50 vertex mesh and you need to draw this say 50,000 times, you could get the CPU to create a buffer of 50 vertices * 50,000 and submit that large buffer to the GPU. You would still only need to do that once because the grass does not move, so you incur the hit one frame only. However that still means you are using a large amount of GPU memory on repeated mesh data and also some performance as the GPU has to process that large buffer. So instead of duplicating all 50 identical (non-transformed) grass mesh vertices 50,000 times, why not simply store a single instance of the grass mesh vertices on the GPU, then get the CPU to create just a position (and possibly rotation, color vertices) for each 50,000 grass object instead of the full 50 vertex grass mesh. So instead of 50,000 * 50 * vertex_size you are submitting and storing 50,000 * vertex_size on the GPU (simplification but the general idea). The GPU still needs to process this 50,000 buffer but it is now much smaller using far less GPU memory and the GPU spends less time doing so. It then takes that single mesh instance and transforms it when rendering each instance to the correct location using the single vertex position data. Of course this means that GPU instancing is only useful for world objects such as grass where the mesh is identical for all instances. Providing a per instance rotation vector (and possibly color vector) can make this duplication much less noticeable. I've implemented exactly this for grass recently using Godot and the MultiMesh class it provides. docs.godotengine.org/en/3.5/classes/class_multimesh.html#class-multimesh

[@HallyVee]

Can this be done for billboard trees at vast distances? ... er wait, billboard != mesh, is it :)

[@adelAKAdude]

That was surprisingly enjoyable to watch ... and informative ... Thank you !

[@AndreCastel]

Just discovered your channel and it's exactly what I needed, so thank you for the great content. Please don't change 🙂 the low budget 2000s look and effects is a breath of fresh air. Keep up the good work.

[@TacoTechnica]

Underrated stuff! Was looking into grass rendering and stumbling across this was very helpful, Gonna check out the rest of the grass stuff and also the rest of the channel since your presentation on topics is great!

[@heyjakeay]

Never would I have expected HuniePop and Kizumonogatari backing music to a technical topic like this

[@James-Calvin]

Another wonderful video, Acerola. I have seen this technique used before in games I've played. Your grass looks amazing! I love the yellowing effect you added related to the height. It's amazing!

[@antonynepgen2045]

I love the entire way that you explain everything, I honestly learnt enough that I will remember most of it while it was entertaining - I could watch these for fun for ages

[@MrWaketeu]

Fantastic video ! I knew everything about instancing, but for an unknown reason, I stayed until the end of the video ! Please continue to make such great content

[@DreamPharaoh]

That was great, thank you for all of the details too. I will be tackling this problem soon and so it was nice to have a direction on it.

[@Acerola_t]

Good luck! It's something I've been researching for quite awhile.

[@buttforce4208]

Amazing video, I've been looking all over for something like this. Thanks so much for making it, GPU Adrien Brody!

[@icedude_907]

Just want to inform you that both me and a friend were recommended one of your videos today despite never seeing you before. This could be about to hit the algorithm. Watched a few of your vids now, extremely well done content

[@wordydird]

I just looked this up cause I was curious what the 2d plane grass was called, but this was really interesting and I learned a lot more than I expected. Cool stuff man, definitely gonna sub and watch more

[@soul-candy-music]

I love everything about this video, lmao. Super knowledgeable, funky detective and retail store style beats, intriguing kitchen/living room ted talks - instant sub.

[@DarkDax]

Great video mate! Just started looking into shaders so this video was really informative. Some of that math might have gone over my head but still really enjoyable haha

[@JoBot__]

That quick recap on the previous video was very useful, and I got everything I needed. Thank you.

[@HuxleyCrimson]

Top notch content man. We have some real added value information here, and it gets deep enough while clearly conveyed and staying at reach. Kudos to you. Instant sub.

[@aleningi96]

Great video about gpu instancing. I'm getting into shaders rn and this was super useful!

[@maribelmenese4845]

I really love how you put the music you use on the description

[@mariovelez578]

This is an amazing video! I learned almost nothing because I already knew this stuff, but you explained it so well!

[@Acerola_t]

Thanks! The next 2 grass vids go into some more modern techniques.

[@mariovelez578]

@@Acerola_t Just did, commenting on all of them to help the algorithm

[@Whatismusic123]

dragon vale is a fire game

[@mariovelez578]

@@Whatismusic123 Lol, yes it is!

[@gus3000spam]

Cool video, chill and informative. I like your style !

[@KoshakiDev]

The editing is on point. I enjoyed the video as a casual viewer and also enjoyed it as a legitimate tutorial

[@jeffmcguire1599]

Dope videos. Going back to watch others. Thanks for making this stuff!

[@Buttered_Bread]

Super interesting stuff, real glad I came across ur vid!

[@19vangogh94]

I love this "Standing In Room Microphone sprinkled with animations" format, its so unique, you shouldn't loose it!

[@johncreativeproducts5688]

what a great video man! thanks so much!!

[@PMARC14]

The math was surprisingly easy, but what was crazy was the artistry in it by taking into account all the many properties to make it look nice.

[@joeypepperoni6078]

I've been searching for this video for months even though I didn't know it existed. I feel like I've found a secret tome of knowledge in this video and your channel. Thank you Acerola!

[@pcih6176]

I loved your performance in "The Pianist"!

[@Korcunu]

Great video and great editing! Really useful info for me as a hobbyist gamedev although I understood only 10% and probably need to rewatch the video multiple times xD

[@jarrednorris]

glad this popped onto my recommended. Inspired me to work on some more code. Keep it up and enjoy 1 more sub!

[@allepiccondor1166]

Great video man can’t wait to see more

[@Kenji_195]

Videos like this really motivates me to keep experimenting with Unity, it was very interesting and fun to watch!!

[@ghwii]

As a game Dev, and also someone who really digs math and algorithms, you can't even begin to grasp how grateful I am KZbin randomly decided to recommend your channel. All of your videos I've seen are a gold mine. Absolutely awesome content!

[@WizardsCode]

Great work... learned alot. Thank you.

[@KaiMCGRPS]

i saw one vid by you and i'm currently binging your content, your videos are so cool

[@Acerola_t]

Thanks!

[@HarryTheLoser_]

Damn, this helped a lot, you definitely will blow up!

[@arsnakehert]

Love how this video is very much a paper in video format, but not only that, in _interesting_ video format Thanks for making this! \o/

[@adiyn_]

Best intro, amazing humor, cool nick, looking goo- i mean nice content quality, man i'm subscribing

[@towyan8187]

Dude your voice with that BGM is addictively great. It helps me sleep lol

[@RosemaryWilliams49fruits]

+1 for very informative. +sub for comedic style being on point.

[@fluffycritter]

Nice technique. A physical wind simulation could be done by doing some shaders that do a fluid dynamics simulation (e.g. water ripples) within a texture and then use lookups into the texture to determine the sway amount. I've also seen some really clever techniques of using the depth buffer of a camera pointed down on the environment to drive the fluid dynamics based on objects moving around (for example, having large gust-of-wind objects that are only rendered on the dynamics sim texture).

[@kitkittsy]

My immediate thought when animation was brought up was that the sin of the x/z positions of the grass would be used to emulate waves of wind. Perhaps not as accurate as a simulation, but trivially different to implement than height-frequency method used here?

[@realPowerPaul]

Thank you for explaining and sharing in detail! First video I found from you and I look forward to check out your channel later. You earn more subs and if you are consistent, I'm pretty sure you will get them! Stay tuned!

[@voizeh7140]

Holy cow! Your channel are awesome! And also funny

[@sethhannah7191]

This video style is hilarious! subbed :)

[@sethcarson2201]

That quick rundown on Dynamic Details was genuinely the cherry on top

[@ZettXXII]

I learned a lot, thanks mate.

[@jake3255]

I remember in Just Cause 2 they had trees billboarded beyond a certain distance, and just made sure that the texture was always facing directly at you. If you flew directly above a tree, it would be lying flat on the ground and rapidly swivel beneath you

[@Acerola_t]

breath of the wild also used this technique for their trees, pretty neat!

[@purp.squared]

a lot of games also use it, mario 64 does it (i dont blame them, it was 1996) half life 2 does it and a few others

[@mariocamspam72]

really nice explanation of a difficult concept

[@DatBass]

awesome video, i've always wondered how this was possible.

[@2Fast4Youtube]

Okay, you got me with the recap. Subscribed forever now, you are stuck with me

[@six-sided-matrix]

This dude sounds like his boss told him to make a video but sound enthusiastic about it

[@TreesPlease42]

This is cool, thanks!

[@nguyenhoangminhtrung2779]

Thank you for these videos!

[@INeatFreak]

Thanks for this superior tutorial.

[@zerosick]

liked the monogatari references subbed

[@CausticCatastrophe]

I really appreciate these videos. they are a breath of fresh air. :)

[@meerkat22]

Strangely perfect explanation!

[@fredericklyle4001]

10/10 my new favorite youtuber. Needs more cowbell? no, needs more grass. (i'm here from your video about bad grass tutorials)

[@kylejennings819]

As an artist with little code experience longing for a powerhouse grass setup. I would love to see an in depth tutorial including code

[@Acerola_t]

Unfortunately I don't have much interest in doing coding tutorials, I prefer focusing on theory and leaving the rest as an exercise for the reader. This is mainly because when I was learning, I noticed a sheer lack of theory focused graphics content. The core of this implementation is compute shaders which I learned from this great tutorial: kylehalladay.com/blog/tutorial/2014/06/27/Compute-Shaders-Are-Nifty.html Additionally my source code is in the description, it is a little messy but referencing it and reading documentation on functions you aren't familiar with should be able to get you there.

[@etopowertwon]

You can use different textures and add random rotation during placement to make it look less uniform. Also I know this technique since Quake 1 days. There they used it for explosions, as they are spherical by nature. I defitenly remember it seeing in other games, but Q1 is my first memory as it also was the first game I played that had real 3d

[@FedSilVor]

As a person from the future I appreciate that you said that is not a new video if someone's from the future.

[@copycatlyn]

i have no idea how i found you, but i am happy you're did. no clue what you're saying either. this is just great :) not due to your explaining, but due to my stupid and ignorance.

[@idontlikethis980]

I am indeed watching this in the future Thank you for addressing this matter

[@a_random_person_]

That was a great video. Even gave me motivation to look at real grass to compare realism

[@TheHypnotistDK]

Awesome video! Keep going

[@socks2441]

fascinating. its so clever how this stuff works. i feel like the grass could do with some better textures though. also, i dont know how hard it would be to add shadows to them but that would look amazing too. probably completely tank performance though, unless you could bake the shadows and animate them swaying with the wind along with the grass etc.

[@QckSGaming]

Excellent video, that's a sub!

[@MikolajZMiasta]

Great video, thank you a lot!

[@dyna6460]

I love the way you explain things thanks you

[@stoneboi1395]

surprisingly high quality, hidden gem of a channel

[@stoneboi1395]

My tips are to allow more head room in your IRL shots, but i loved the editing and the grass solurion was really cool

[@Acerola_t]

Thanks! I'll take that into consideration

[@Ugric]

This video is really enjoyable, well made and easy to understand! :) Wouldn’t be surprised if you got really popular soon!

[@EthanFilms]

Amazing video!!! Subbed!

[@manuelsalgado9855]

dude, you are my hero

[@user-db9do2hi7b]

Man youre awesome, thanks

[@nathanfan1130]

Amazing informational video but you really used Hunie pop bg music and thought I wouldn't notice XD

[@g45h96]

Super informative video. And it's awesome that your explanations lay outside of the specific engine you're working in. Also you're one letter away from being a nipple, js.

[@ThatPawikBoy]

I love you Sir, thank you so much.

[@hmidi]

enjoyable to see and learning stuff as well .. Good Busy (as we say in dutch)

[@DexFlex_YT-]

you could also use the terrain displacement map for grass yellowness cuz all the water goes down from the hills, so lower=green higher=yellow

[@bunksoup8137]

My favourite part is the wire plugged into a wireless mic.

[@Acerola_t]

It's unfortunately not wireless it's a samson q2u

[@yuukil5522]

Your channel is like the brutal moose of video game design like same humor and same quality

[@Gilesone1989]

Interesting video to understand what's going on behind the scene

[@bluebaby30]

Great video, P3 music was the cherry on top

[@ktz1185]

2:01 "In order to render grass, you need grass to render" fucking love it

[@alice20001]

Yay! I'm the one from the future. Also, that's the swaggiest way to intro a video. LovedIt!

[@AB-td5oo]

i have been searching for this video for a year now... finally found it

[@KnifeChampion]

I am indeed watching this in the future! how did he know?!? :O

[@centur]

good vid, subbed

[@Tenetri]

cool vid dude, keep it up!

[@Denester31]

This is a great tutorial! You gained new sub. How you achieve GPU instancing for grass?

[@Acerola_t]

Thanks! If you're interested in doing GPU instancing with Unity, check out these functions: docs.unity3d.com/ScriptReference/Graphics.DrawMeshInstanced.html docs.unity3d.com/ScriptReference/Graphics.DrawMeshInstancedIndirect.html

[@emiel333]

Awesome. ❤. I’ve subscribed

[@billzoaiken]

Comment for the YT algorithm and to say thanks for the great content!

[@DavidRutten]

That arrow with the fake alpha cracks me up every time.

[@bluebukkitdev8069]

So I've been looking for someone who is competent with graphics programming and is happy to explain in detail for some time now. Everyone on YT right now either doesn't go into detail, or uses too much technical jargon, or is outdated by at least 6 years. This was a good find. Have a free sub.

[@EpicDragonfly]

amazing video!!