Minecraft shaders via Prism/Iris setup stopped working

[ssscott75044]

Basics: I have the 64GB LCD Steam Deck. I'm playing Minecraft with the Prism Launcher, which is on the Discover Software Center and gets automatic updates. It links to my Microsoft account to verify that I own Minecraft. I've had to redirect the 'instances' folder to my external SD card because my resource pack takes up too much of the precious 64GB internal space. The Iris mod is required to use shaders, which give Minecraft realistic lighting and bring textures to life with normal and specular maps. I've yet to find anyone with a Steam Deck who's also doing this. I think Valve should take interest in this subject, because Steam Deck is very well suited to running 'fancy' Minecraft. In fact, I think it should be a strong selling point for the console.

What happened: I ran an instance of Minecraft 1.19.3 for many months successfully with SEUS PTGI shaders loaded from file. I shifted to Minecraft 1.20.1 also successfully for many months. Then one day, I think about a month ago, when I loaded the game the world was unviewable. The screen splits into two triangles and flickers. I had to disable shaders to keep playing my world. Other than shaders, everything seems to work fine. I changed nothing, just loaded the game like normal. The only changes were Discover Software Center regular updates, including Prism Launcher.

Debugging1: After waiting a couple of weeks for whatever changed to be fixed, I've given in and messed with everything I could think of. I moved my regular game to Minecraft 1.20.2, then to 1.21, with the latest versions of all mods. I've created new instances of 1.21 and other versions from scratch with the most basic Iris setup. I've used my old SEUS PTGI file, and I've tried loading BTS shaders from the Prism menu. When either is enabled in the game, I get the inscrutable flickering screen.

Debugging2: This week I tried running the old 1.19.3 instance. The last time I ran it was many months ago when I made a copy of it to move to Minecraft 1.20.1. Shaders worked on it the last time I ran it. I've not touched it. So, if something has gone wrong with mods since then, it should still work. It doesn't. It does the same flickering screen. This therefore has to be either a hardware or system software problem. I don't think it could be hardware, because I've had no other display problems.

Debugging3: It's possible that this is a file permissions problem, which Prism deflects as a SteamOS problem. When I click any 'open folder' button on Prism, nothing happens. Others have had this problem, and through researching that, I installed the Flatseal program and changed settings for Prism to give it access to all system and user files. Hasn't helped. Also, I don't know why that would only impact shaders.

Status: I've gone to Prism for help, and they deflect me, saying it couldn't be a Prism problem. I've gone to Steam support for help, and they deflect me, saying it's a third party software problem. I've gone to forums and asked other Iris users (none of whom have been using it on Steam Deck) and they have no problem. If I could find anyone else who's running shaders on Steam Deck, we could either confirm that we both have the problem, or if it's just me I could mimic their setup.

[ssscott75044]

Update: I got a tip that the June 14 Steam Deck Beta Client Update made a change WRT shaders (I suppose in games other than Minecraft). Could that have affected Prism/Iris on Steam Deck?

[Elucidator]

Supplementary Information:
(No, I don't own a deck, so I can't test, but I can explain stuff.)

Minecraft has two editions. Bedrock and Java.
The affected edition of the game is the Java Edition. As the name suggests, minecraft java requires Java.
Minecraft Java version 1.19 requires JDK version 1.17 to run. The official minecraft launcher bundles OpenJDK with the game.

By default Minecraft does not support shaderpacks, however, 3rd party mods can make it so that minecraft supports this. Currently Iris is the most popular mod to add Shader Support. The alternative, Optifine, has had issues in the past, which is why this is the current case.

Generally, Iris requires the Fabric Modloader on top of Minecraft, though there are ports of Iris for the other modloaders.

Please setup your minecraft test environment as follows:
- Install Java
- Install Minecraft ( https://www.minecraft.net/en-us/download/alternative )
- Install Fabric modloader ( https://fabricmc.net/use/installer/ )
> run minecraft, then close minecraft
- Add the Iris mod to the now generated 'mods' directory ( https://modrinth.com/mod/iris )
(this directory is inside the minecraft profile's game directory)
> run minecraft again (so that the shaders directory generates)
- Add a shaderpack ( https://minecraftshader.com/seus-ptgi-shaders/ )
- create a new singleplayer world and enable the shaders.

It doesn't really matter which 'game launcher' you use, but some game launchers like Prism make the process of installing these easier. Please look up a guide.

Summary of the issue:
- Minecraft Shader visuals break during gameplay.
- Suspected since Deck Update: June 16 (beta). (stopped mattering)
- No changes in the mod (Iris), Minecraft or the shaders occured at that time, only the Deck updated.

Possible cause: Permission Settings.
For that reason, you may need to find out where and how minecraft + said modpacks install, especially through the Prism launcher.

Edit:
More info about the prism launcher can be found here:
https://prismlauncher.org/
and their respective github page.

Edit 2: True cause determined.
See my post below.
https://steamcommunity.com/app/1675200/discussions/1/4517756980046346729/#c4517756980047951250

[ssscott75044]

I asked Valve for help with this, and they said it's beyond their scope. I've opened a bug report on the Iris github.

[Elucidator]

Apparently the issue is caused by a bug within Iris
https://github.com/IrisShaders/Iris/issues/2411

The issue happens on All AMD GPU + Linux machines according to the developer.
He suspects it's cause may be rooted in the use of Mesa 3D Graphics Library, but so far he isn't sure yet.

Conclusion: It's not caused by the Steam Deck update, and has nothing to do with permissions as such.

You'll have to wait till someone with knowhow fixes it.

Edit:
The developer of Iris narrowed it down to indeed be a bug from the Mesa 3D Graphics Library, and... they're working on it apparently
https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests

What I find interesting though, is that this all means something;
namely that the OP's instance of minecraft must have had a change, or the bug was already present and he didn't notice.

[Gajahamwy]

i am on steam deck and am having the exact same issue. did you ever find a solution?

[Elucidator]

Originally posted by Gajahamwy:

i am on steam deck and am having the exact same issue. did you ever find a solution?

The issue should be fixed. Update Mesa to 24.2 on your Steam Deck ( https://docs.mesa3d.org/relnotes/24.2.1.html )
and Iris to the latest version.