3D render textures in a compute shader?

[unreal zodiac]

I'm creating a 3D render texture, and I'm trying to generate some noise on it in a compute shader so I can use the rendertexture in a shader I'm working on. But I can't figure out how to get it going! This is currently what I'm doing to create the 3d texture:

RenderTexture tex = new RenderTexture(volumeSize, volumeSize, 0, RenderTextureFormat.RHalf, RenderTextureReadWrite.Linear);
tex.enableRandomWrite = true;
tex.dimension = UnityEngine.Rendering.TextureDimension.Tex3D;
tex.volumeDepth = volumeSize;
tex.Create();

shader.SetTexture(shader.FindKernel("CSMain"), "Texture", tex);
shader.SetInt("volumeSize", volumeSize);
shader.Dispatch(shader.FindKernel("CSMain"), volumeSize,volumeSize,volumeSize);

im not sure how to get this thing to properly render though

this is the actual shader itself

// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel CSMain
// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture
RWTexture3D<float4> Texture;

int volumeSize;
[numthreads(10,10,10)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    float x = id.x / volumeSize;
    // TODO: insert actual code here!
    Texture[id.xyz] = float4(x, 0, 0, 0);
}

but for some reason, it just shows up as white in the inspector

[devout zephyr]

your numthreads seem strange lol

but anyway, you're looking at the texture during play mode right

quite confused actually

your texture cpu side is an rhalf but on the gpu side its a full rgba32

@unreal zodiac cursed

[unreal zodiac]

dude idek what a rhalf is i was googling like everywhere and i found someone that used that and just kinda went with it

[unreal zodiac]

i'll literally never understand how the threads work at all i just heard 8 was a good number

[unreal zodiac]

and also yeah i am looking at it in playmode

sorry for the ping bomb lol

[devout zephyr]

you need to understand how they work because you can't just guess. they need to be correct. like you're dispatching a total of 15,625,000 threads for your kernel right now which your graphics card definitely refuses to do

[unreal zodiac]

that doesn make sense...

oh wait thats bc this is 1x1x1 hang on

[devout zephyr]

you need to understand how it works because you can't just guess. it needs to be correct. like you're using a texture that has 2 bytes per element on the cpu side and on the gpu side you're treating it like a texture that has 16 bytes per element. not going to be a fun time

[devout zephyr]

good 😄

[unreal zodiac]

right so i gotta learn a bit more

im mainly using this to generate noise, so all i really need is just one float

but im not sure if there's a texture format that supports just a grayscale value

[devout zephyr]

so on the cpu side you got it right

[unreal zodiac]

oh so i just gotta change it to that

[devout zephyr]

yeah exactly

[unreal zodiac]

ok so that's the format done

[devout zephyr]

see how they match now

[unreal zodiac]

yay!!!

[unreal zodiac]

also this makes sense because this actually does work for a 2d texture

so that might be the trouble

im not necessarily sure how to figure out what thread size i need

[devout zephyr]

volumeSize is 25 right?

[unreal zodiac]

yeah

[devout zephyr]

https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/sv-dispatchthreadid

i suggest understanding that diagram

but as a tdlr

a thread is the basic unit in the gpu
threads are organized into groups
the numthreads(x, y, z) determines the dimensions of these groups
you dispatch groups of threads. dispatch(x, y, z) determines how many groups of threads you dispatch

so in your case, you thread groups are 10x10x10

and you dispatch 25x25x25 of them

[unreal zodiac]

ok that makes sense

[devout zephyr]

which totals to just a ridiculous number of threads

[unreal zodiac]

yeah im starting to see how i fucked up lol

what if i did a thread group of 1x1x1? and then did 25x25x25?

[devout zephyr]

okay so there's lots of ways of organizing this right

you could also do a thread group size of 25x25x25 and dispatch only one group

now, threads that belong to the same group actually get all kinds of advantages, like memory and performance stuffs

but, there's a max number of threads that can belong in a group

[unreal zodiac]

i dont think im able to do 25x25x25

yeah

[devout zephyr]

so that's your job to figure out how to do this efficiently

one option could be 7x7x7 and dispatch 4x4x4, but that would leave 6327 or 28.8% of your threads dispatched unused

[unreal zodiac]

i dont even know the math of how to figure that out

[devout zephyr]

basically you need 25x25x25

[unreal zodiac]

maybe 8x8x8 and 3x3x3? does that even work?

[devout zephyr]

but there's a maximum to each thread group which i'll leave you to find out

[devout zephyr]

that would only be 24x24x24 right

[unreal zodiac]

the max is 1024

[unreal zodiac]

oops

i mean i could just drop it one

[devout zephyr]

haha that's one option

powers of two are always nice

[unreal zodiac]

hmm alright

i do sorta wanna save the figuring out for a bit later, ive dropped the res to 24 and im now using 8x8x8 and 3x3x3

yet for some reason, it still doesnt really want to render

[devout zephyr]

show your code

[unreal zodiac]

sure, gimme a sec

tex = new RenderTexture(volumeSize, volumeSize, 0, RenderTextureFormat.RHalf, RenderTextureReadWrite.Linear);
tex.dimension = UnityEngine.Rendering.TextureDimension.Tex3D;
tex.volumeDepth = volumeSize;
tex.enableRandomWrite = true;
tex.Create();


shader.SetTexture(shader.FindKernel("CSMain"), "tex", tex);
shader.SetInt("volumeSize", volumeSize);
shader.Dispatch(shader.FindKernel("CSMain"), 3, 3, 3);

compute code:

// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel CSMain
// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture
RWTexture3D<half> tex;

int volumeSize;
[numthreads(8,8,8)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
    // TODO: insert actual code here!
    tex[id.xyz] = id.x / 24;
}

[devout zephyr]

zero the texture in the shader

[unreal zodiac]

still white

by zero, you mean output zero?

bc that's what i just did

[devout zephyr]

maybe switch to just the R channel?

im not sure how to visualize a 3d texture

that's weird to me

[unreal zodiac]

think of a 3d array and call it a texture

thats pretty much what i understand of it

[unreal zodiac]

yeah ill try that

its full white in all channels

[devout zephyr]

try it with a 2d texture first

[unreal zodiac]

already did, works

also

updated unity, it works

and it has a nifty 3d view

and you can view all the slices and everything

[devout zephyr]

oh what

how did you update

[unreal zodiac]

unity hub

[devout zephyr]

you're just going to see one side of the cube as a little black but everything else white

[unreal zodiac]

i was making it on 2019 because when i used the new versions the slowdowns were incredible

[unreal zodiac]

i am?

[devout zephyr]

should be?

[unreal zodiac]

oh no i changed the size of the volume to 24 so that extra one isnt there

[devout zephyr]

oh hmmm true

[unreal zodiac]

thanks for helping out though you're a lifesaver

[devout zephyr]

i did a lot of work to figure this stuff out so i thought id try to help make it easier for other people

imagine just staring at a black texture not even having a debugger or anything

but compute shaders are literally my favorite

[unreal zodiac]

it sucks ive had to download RenderDoc now

[devout zephyr]

i probably should download it

i just use the texture itself to debug

colors mean different things

[unreal zodiac]

yeah maybe

one thing i wanted to ask, im using keijiro's noise library to generate some perlin noise

and i believe i import it using this

#include "Packages/jp.keijiro.noiseshader/Shader/ClassicNoise3D.hlsl"

did that, tried referencing a method but its not doing anything and i dont know if its because compute shaders can't do #import or if it just isn't working

@devout zephyrhave you had any experience in it?

[devout zephyr]

just rip the code right off the shader

or move the shader into the same folder

likely your path is wrong

probably need a bunch of ../../../

[unreal zodiac]

tbf probably a good idea

[unreal zodiac]

what does moving it into the same folder do?

also just copied it all into the same folder and it still aint working, ill have to look for something else

[devout zephyr]

most likely your path is wrong. if you move it into the same folder, you can just do #include "ClassicNoise3D.hlsl"

[unreal zodiac]

hm right

[unreal zodiac]

yeah moved it in the same folder, still all black

definitely the noise shader's issue, as doing a sine wave based on the position works normally

[devout zephyr]

copy the code directly

[unreal zodiac]

yeah did that

nothing

no errors though

[devout zephyr]

write your own code lol

[unreal zodiac]

i cant!!! i suck at it!!!

one thing i wanna ask though this is really weird

more or less a whole seperate issue but still related to it

[devout zephyr]

life tip: if you need to preface a message with that you better think really hard about saying it

[unreal zodiac]

no no no its not like

its not weird like that its like

ok right so i copied the thread settings to another compute shader im doing

and made another 3d texture, just like this, same thing

tex = new RenderTexture(volumeSize, volumeSize, 0, RenderTextureFormat.RHalf, RenderTextureReadWrite.Linear);
tex.dimension = UnityEngine.Rendering.TextureDimension.Tex3D;
tex.volumeDepth = volumeSize;
tex.enableRandomWrite = true;
tex.Create();

used settexture, and in a compute shader im doing this

tex[id.xyz] = sin(id.y);

which only... sorta works

im not sure what's wrong with this at all

like the code is only running for a certain part of it?

but that doesnt make sense, it's the same size and thread settings as before

ok turns out i actually did mess up the thread settings please ignore me

[devout zephyr]

is it working

[unreal zodiac]

...sorta

give me a second

yeah, its working, but the previous system i used was only created with 1 thread group on the X in mind, but now that there's 3 thread groups on each axis it's sorta broken

like im passing a 3d array into the compute shader using a compute buffer, but i dont think that preserves the dimensions

so in the shader, i need to reference it with a 1d index

[devout zephyr]

wait how

i don't think you can pass a 2d array?

[unreal zodiac]

no, you can pass a single array

that's the thing, the array is 3d in unity but 1d in the comp shader

[devout zephyr]

show code

how are you passing in a 3d array when it takes a 1d param?

also just use a 3d array on the compute shader side then

[unreal zodiac]

public VolumeCell[,,] cells;

ComputeBuffer cellsBuffer = new ComputeBuffer(cells.Length, (sizeof(int) * 3) + (sizeof(float)));
        cellsBuffer.SetData(cells);

[unreal zodiac]

i didnt think it was possible

[devout zephyr]

what

alright but you have no idea how that data is laid out

i'd just perform your own flattening operation for sanity

[unreal zodiac]

i mean you said there was a 3d array equivalent for compute shaders so i'd rather use that

[devout zephyr]

no you don't know how the data is laid out

remember, memory is linear. and that is how it is transferred between cpu and gpu, as a linear chuck

there are many ways to flatten a 3d array to a 1d array, and there are many ways to take that 1d array and interpret it as a 3d array

you cannot be sure that the cpu and gpu are using the same methods

unless of course, you code both methods

[unreal zodiac]

you've got a true

i'll write that out real quick

[unreal zodiac]

im trying to write this out but im sorta getting stuck turning the 1d back to the 3d

[devout zephyr]

don't do it that way

it is an array of 2d arrays

and the 2d arrays are just arrays of 1d arrays

heres some inspiration for your shader journey

[unreal zodiac]

WOAGH!!!!

[unreal zodiac]

yeah i just copied code from the internet i ran out of stamina

ive made it so it iterates on the X, then the Y, then the Z

which is coolio, but now i gotta do this in the shader which im sorta stuck on

@devout zephyrwould something like this work for converting the 3d array index of the compute shader into a 1d one for the array?

int get1DIndex(uint3 pos)
{
    int index = 0;
    for(int z = 0; z < pos.z; z++)
    {
        index += volumeSize;
    }

    for(int y = 0; y < pos.y; y++)
    {
        index += volumeSize;
    }

    index += pos.x;
}

[devout zephyr]

no

[unreal zodiac]

ouch

[devout zephyr]

well hmm

assuming volume size is 24, decode 48

[unreal zodiac]

wdym decode 48

the size on each axis is 24 so it's adding...

wait wait wait, i think i need to do volumeSize squared on the Z loop

[devout zephyr]

yeah there you go

[unreal zodiac]

Yay!