How can i tamper with polygon drawing order with shader?

[quiet bone]

I want to alter polygon rendering order a little bit, replacing whats called Z-Buffer

[formal crag]

if you set the depth test mode to always to ignore depth and change the render queue on the material then you can make something render later.
https://docs.unity3d.com/ScriptReference/Rendering.RenderQueue.html

[quiet bone]

i need to manually sort them

[formal crag]

Then set their render queue to a value that does what you desire. Or render the meshes yourself with Graphics.DrawMesh() and without depth testing they will be in the order you desire.

https://docs.unity3d.com/ScriptReference/Graphics.DrawMesh.html

[quiet bone]

i mean manually sort polygons, not meshes

i want to make whats called "artist alghoritm"
its a cheap alternative to Z-Buffer, that renders polygons from farthest to nearest

[formal crag]

Wha well then you need to make sure the indicies are in a specific order in the mesh

[quiet bone]

you mean ccw?

because of backface culling?

[formal crag]

Well i presume you want to control the order in which triangles perform their fragment

otherwise i am lost as to what you want

[quiet bone]

wait a min

here is an example of the game that uses artist alghoritm instead of Z-Buffer

[formal crag]

Looks weird in places as id expect

there is a reason why depth writing and testing exists

[quiet bone]

i know

and i want this effect

[formal crag]

using shader graph you can disable depth write and make depth test always pass and it should produce a similar effect.
It would require careful ordering of mesh drawing however and im not sure how to achieve the effect any better myself.

[quiet bone]

no, it sorts polygons, not meshes

[formal crag]

we dont have "polygons" we have triangles

[quiet bone]

ok, that changes nothing

that is what i meant

[formal crag]

transparent rendering already does something like what you want. Unity will draw meshes in order based on distance from the camera and they don't write depth.

id play around and see what you can get

[quiet bone]

how can i do that?

[formal crag]

using standard/urp lit/whatever you can change it to transparent and that should already disable depth writing.
It still will depth test but because the mesh is not writing depth as it draws its triangles can be in the "wrong order".

Or with a shader graph shader you can customise depth writing and depth testing (as shown in the image)

[quiet bone]

and how do i disable depth test in a regular shader?

[formal crag]

There are keywords to change these also in text based shaders I forget what they exactly are rn

[quiet bone]

uhh, it didnt gave me effect i needed

i need for triangles to derp, not whole meshes

[rapid vault]

What's the difference?
The whole mesh is nothing but triangles

Ah, so triangles not sorted per-mesh but equally between them

[gentle dagger]

"ordering polygons/triangles in a mesh during rendering" doesn't make sense. Vertex shaders run many threads for several vertices(and as a consequence, triangles) at the same time. That's exactly what makes the GPU faster than Cpu. Making them run in order, would kill performance.
You could probably implement software rasterization on the cpu, but prepare to lose a lot of the frame budget to it. And I'm not sure how you'd approach it in unity anyway.

[quiet bone]

no

[rapid vault]

I'd guess maybe render all meshes procedurally as one, and sort the triangles using a compute shader to win back some performance

[quiet bone]

i mean mesh either fully visible either fully invisible

[rapid vault]

Meaning that's how it should be, or is but should not be?

[quiet bone]

i know, i mean somehow change their draw order

[quiet bone]

look at the screenshot

[quiet bone]

here is what i want to achieve

note that some triangles acting a little werid

[quiet bone]

yes

[rapid vault]

I think I understand
No clue how feasible it is to do though

[quiet bone]

my only (and totally not the best idea) is to separate all the models into spare triangles

[rapid vault]

Maybe the combined mesh idea has a chance of working, or you could look into what kind of control a custom SRP would give you over rendering

[rapid vault]

That seems intuitive, but probably the worst way to do it

[gentle dagger]

So we're not talking about triangles, but meshes/draw calls?

[formal crag]

no it is about triangles its very confusing 😐

[quiet bone]

yeah... I want to mimic "artist's alghoritm", pretty good alternative to hardware Z-Buffer (but the only point to have it if you are making your own 3D engine with only CPU)

so it basically "sorts" all triangles, and then renders them in strict order that sorting gave

[gentle dagger]

I don't think it's a "good alternative" for hardware depth testing.
And the purpose seems to be completely different. The former one is an optimization technique. The latter seems to be an artistic visual effect.

You could try disabling depth testing, backface culling and making the shader transparent. This would get closer to your desired effect, but the screenshot you shared earlier seems to be more than just that.

What is the goal you're trying to achieve anyway? Is it the specific visual look or are you assuming that would improve performance?

[quiet bone]

I want it for an effect. In a game i showed it was used to replace Z-Buffer (this game is just PoC)

[quiet bone]

no, backface culling should be on

[quiet bone]

visual

[gentle dagger]

You can't say "used to replace", as they serve different purposes. It "had to disable" depth/z testing for the effect to work.

[quiet bone]

no

you can look at sources: https://github.com/vectozavr/shooter

the sfml branch one

[quiet bone]

in context of the game i shown without artist algho would look even worse

[gentle dagger]

Looking at the screenshots in the repository it just looks like a bunch of transparent geometry to me.

No "custom triangle ordering"

[quiet bone]

what???

look at that

exactly, the gun

[gentle dagger]

Definitely nothing special in the gun

[quiet bone]

definetly you are blind

[gentle dagger]

3D game engine with custom CPU rendering
So you can virtually do anything with it. At the cost of performance. I don't think it's worth using unity if you want to reimplement it.

[gentle dagger]

Maybe show me what exactly I should be looking at and why..?

[quiet bone]

ok

[quiet bone]

also on the green ramp there is a big dent

[quiet bone]

no, it was an indeed solution because cpus dont have hardware depth test, so smth like that was mandatory

[gentle dagger]

Ah I see. It looked like just overlapping polygons first(I'm viewing it from my phone).

[gentle dagger]

Yes, it's a poor(or intentional) implementation of depth test.

[quiet bone]

more like poor

depth test is running for each pixel

and artist alghoritm only running for each tri

[gentle dagger]

But that doesn't change the fact that it's a cpu rendering technique and you can't really adapt it to use in unity. You could implement software rasterization in C#, writing to a texture and then rendering the final image normally on the gpu(via a ui raw image) for example. But why..? Can't you just use that engine instead?

[quiet bone]

then the answer to the thread is no

because i cant somehow manage tris

if i wanted to make my game in godot, i would just rewrite the engine lmao

[gentle dagger]

You can. You can totally modify triangle order in a mesh. It's just that it wouldn't help much with GPU rendering.
And with cpu rendering you might not even need to. You can have a separate collection of indices or some other mechanism to render them in the order that you want.

It all falls down to implementing the cpu renderer.

[quiet bone]

the game was written in C++

and if C++ gave hudge bottleneck in fps, then C# implementation will be 1 fps

[gentle dagger]

There wouldn't be much difference.

You seem to misunderstand the difference between C++ and C#.

And if you really wanted to, you could write it in C++ and use as a native plugin.

But yeah, it's gonna be heavy either way. There's a reason no one is rendering games on the cpu.

It might be feasible in a very simple scene with minimal rendering features, but even then you'll get less frame time for other stuff in your game.

[quiet bone]

C# is jit

[gentle dagger]

1. You can compile your game with il2cpp, and probably should.
2. You're underestimating modern JIT.

[quiet bone]

if original game gave me around 80 fps, its rewriite in C# will at maximum will give me 60 fps

[gentle dagger]

There might be like 10-20% difference, and even that in edge cases. Most C++ code isn't even using C++ to its max capabilities. Same about C# though.

[quiet bone]

anyway im just too lazy to do so

[gentle dagger]

Sure. But then there's il2cpp and native libraries that could mitigate it almost entirely.