[MC 1.17] Iris overrides vanilla shaders, causing texture bugs for displayed (custom) armour

[Andre601]

What happened?

When using any kind of shader pack while playing on a server using a resource pack to implement custom armour, will the displayed armour look broken and as if the textures got misaligned or something.

From own testing, and through additional information by @LoneDev6 does it seem to happen with pretty much any shader and could be related to overriding the rendertype_armor_cutout_no_cull shader, even while it is present in the server's resource pack.

Additional information, including possible reproduction steps, can be found in the following issue: sp614x/optifine#6391

Screenshots

How the armour should look like:

How it actually looks like with shaders enabled:

Relevant log output

Don't see any relevant log entries worth mentioning here.

Iris and Minecraft Version

iris-mc1.17-1.1.3.jar for MC 1.17.1

Are you running Sodium along with Iris?

Yes

Operating System

Windows 10

What is your GPU?

NVIDIA GeForce GTX 1060

Java Version

16.0.1 (64 Bit)

Additional context

I reported this to the dev of the server plugin that allows custom items, armour, etc. through generating a resource pack and he mentioned that this needs a fix on your end, as the same also happens on OptiFine's end too.

[AlsoSylv]

Vanilla core shaders can not work with an Iris/OF shaderpack enabled, they have to be disabled for shaders to work properly

[coderbot16]

This is not feasible to fix on our end without hardcoding specific fixes and patches for every single server that abuses core shaders to do custom things.

[LoneDev6]

There is surely a way to fix this, maybe a complicated way that needs to rewrite parts of the game rendering engine, but this is still an Iris and also Optifine problem.

We sadly cannot accept your answer:

This is not feasible to fix on our end without hardcoding specific fixes and patches for every single server that abuses core shaders to do custom things.

This is a vanilla resourcepacks FEATURE not an hack nor it can be considered "abusing".
Mojang gave us access to shaders via vanilla resourcepacks so we can do whatever we want with them.

We are supposed to use shaders like this. Let's say I make a vanilla shader to make all armors red or a shader to show a wireframe view of the world, they would be valid shaders and not an abuse of the feature, but still it won't surely work with Iris nor Optifine because you override the shaders completely.

So I think this must considered a bug/limitation and you should consider to try to find a solution to support vanilla resourcepacks shaders feature (Mc 1.17+).

Thanks for your time

[IMS212]

A GPU cannot run more than one shader at the same time, that is a hardware limitation. What you are asking is practically on AI levels of modifying 2 shaders and combining them.

[LoneDev6]

What?
I'm not asking to run more than one shader, where did I say that?

The mod should check each loaded resourcepack to know which shaders they are implementing and stop overriding these particular shaders, then let the game load them from the resourcepack.

Which is basically what the game is already doing with the builtin shaders.

[IMS212]

This would lead to the optifine shader not running and visual glitches taking place, due to optifine shaders assuming it’s being ran correctly.

[LoneDev6]

This would lead to the optifine shader not running and visual glitches taking place, due to optifine shaders assuming it’s being ran correctly.

This statement has nothing to do with my previous messages

[DioEgizio]

You can't just use two shaderpacks at the same time

[AlsoSylv]

Shaders in both the optifine and iris format assuming everything is running properly, "disabling the part of the shader that the resource pack is using" is not feasible, and would break many shaders.

As coderbot said, shaders would have to be patched on a case by case basis to properly handle core shaders running along with iris shaders, which is not feasible.

[IMS212]

It does. OptiFine shaders use composite passes, and the majority of shaders assume the rest of the shader… actually works during the composite pass. If it doesn’t, things usually end up miscolored, misshapen, or even outright invisible.

[coderbot16]

This is the result of Iris not overriding the terrain shader and letting the vanilla one apply:

Similar issues apply to entities. Hopefully, you can see that this isn't a workable solution. The problem is, shader packs expect specific data to be written by shader programs, but core shaders have no knowledge of that.

You are right that there might be a way to fix this. But in computer science, some problems have no general solution. Which means, we'd have to look at every possible variant of these core shaders and manually hardcode a patch for each and every override used by server owners and resource packs. Since there are infinite possible overrides, we'll never actually solve this problem, and will just be wasting our time playing whack-a-mole.

As a result, we've decided to not support this, because doing so with the way that Mojang has laid out core shaders is infeasible.

[coderbot16]

Also, do note Mojang does not officially support replacing core shaders either, even though it currently works:

Shaders are now included for all supported render states. Any shader except for the blit shader can also be replaced in resource packs. For now replacing these shaders is not officially supported and the way it works may change in the future.

https://www.minecraft.net/en-us/article/minecraft-snapshot-21w10a