Driver level bugs causing issues in Minecraft & OpenGL shaders

[djmrFunnyMan]

First of all, yes the game is modified. Its running Sodium (rendering optimization mod) and Iris (OpenGL shader pipeline). Both of these mods are stable, and developed by professionals. The mod developers confirmed the issues must be fixed on intel side as they cannot do anything about them.

- I am using the latest WHQL driver.
- I do not need to use DDU. I assembled this PC 2 weeks ago, it's completely fresh and has no old drivers on it.
- SSU log attached igcit_ssu.txt

Issue 1: Poor frame presentation

This issue might be present in vanilla minecraft (though much less severe)
I can't be sure for certain if what I'm seeing in vanilla minecraft are issues with frame presentation. I'll stick to the case with sodium installed as it's much more apparent there.

This issue is apparent even without shaders, (as in, without iris, only with sodium) the frame persentation layer in the Xe-HP driver is busted. Frames will present extremely erratically. This manifests in the game's motion appearing jittery, despite no frametime spikes being present to explain the jitter. The workaround is to increase render ahead limit to 4 or more and cap the framerate to somewhere below the average, which still doesn't solve the issue entirely.

Video of the issue: https://drive.google.com/file/d/1VsygjDYucoz82VyD47mD38dcq22nVkb_/view?usp=sharing

To observe the issue these criteria need to be met
- The framerate mustn't be the in the hundreds. So you either need to run shaders or have a very high render distance in an intensive scene.
- The framerate mustn't be capped below the uncapped average framerate.
- Render Ahead Limit musn't be set to 4 or higher.

Even after increasing the render ahead limit the frame presentation appears to be somewhat funky especially during lag spikes.

Issue 2: The OpenGL mix() function seems to not work correctly.

It produces NaN's in situations where AMD and Nvidia cards don't have such issues.
In this particular case the line of code affected is line 21 in blocklightColors.glsl (in the attached shaderpacks.zip)

vec3 torchBlockSpecialLightColor = mix(vec3(2.0, 0.87, 0.27), fireSpecialLightColor, 0.75);

(showcase image attached NaN.png)

Issue 3: Night Nebula function from Complementary Shaders is broken on certain nights.

This issue also isn't present on Nvidia or AMD cards.
The function that drives this effect is located in nightNebula.glsl (in the attached shaderpacks.zip)
(3 showcase images attached)

Reproduction Steps

Preparation:
- Install Iris & Sodium for 1.21.4 : https://github.com/IrisShaders/Iris/blob/multiloader-new/docs/guide.md
- Unpack the shaderpacks.zip inside the (...)\AppData\Roaming\.minecraft folder
- Unpack the Driver Bug Test.zip inside the \AppData\Roaming\.minecraft\saves folder
- Go into options>video settings>shaderpacks and select "complementary unbound 5.4 + euphoria patches 1.5.2"
- Press apply

Issue 1:
These settings concide with the performance of my B580. I'm bringing the FPS to around 100. On older cards you may not need to set render distance to such high value to achieve this FPS.

With Sodium & Iris:
- Enable Shaders to lower your framerate
- Create a new world
- Set render distance to 32
- It is advised to turn off view bobbing (press Shift + P in video settings tab to access the setting)
- Fly around in a circle while rotating your camera

If you go to "options>video settings>advanced>render ahead limit" and change that to 4 or a higher value the issue will be greately alleviated.

Possible vanilla reproduction steps:
- Create a new world
- Set render distance to 32
- It is advised to turn off view bobbing
- Fly around in a circle while rotating your camera

If you look closely will notice "jitters" in the frame presentation where the game seems to present an older frame. If you open the frametime graph with F3 + 2 you'll notice these jitters don't correspond to any lag spikes

Issue 2:
- Open the Driver Bug Test world in-game
- Step on the pressure plate that says "NaN apocalypse"
- Press the button to place a torch

Issue 3:
- Open the Driver Bug Test world in-game
- Step on the pressure plate that says "Broken Night Sky"
- Step on any of the pressure plates and you should notice graphical issues on the sky

Should you wish to contact the developers about any of these issues, tips regarding issue 1 should go to the sodium developer (https://github.com/CaffeineMC/sodium) and issues 2 & 3 should either go to the iris developer (https://github.com/IrisShaders/Iris) or the shader developer (https://www.complementary.dev/contact/)

[DhannielM_Intel]

Hello djmrFunnyMan,

Thank you for your detailed post and for providing the reproduction steps for this issue. Your thoroughness is greatly appreciated. I will now investigate this further on my end to better understand and address the problem.

Best regards,

Dhanniel M.

Intel Customer Support Technician

[DhannielM_Intel]

Hello djmrFunnyMan,

I have reviewed your issue and determined that it would be best to move your thread to a more specialized forum. To ensure you receive the most accurate and timely assistance, I will be transferring this discussion to our Developing Games on Intel Graphics Forum. This dedicated forum is staffed with knowledgeable community members and experts who can provide you with the support you need. Thank you for your understanding.

Best regards,

Dhanniel M.

Intel Customer Support Technician

[djmrFunnyMan]

I would like to add more information regarding issue 2 because the more we learn about it the less sense it makes

vec3 torchBlockSpecialLightColor = mix(vec3(2.0, 0.87, 0.27), fireSpecialLightColor, clamp01(0.75));  //this works as expected

Doing this will fix the issue and make it behave as expected. This fix makes zero sense however as clamp(0.75, 0.0, 1.0) should do absolutely nothing to the 0.75

clamp01 is just a simple function that looks like this (it's in commonFunctions.glsl)

float clamp01(float x) {
    return clamp(x, 0.0, 1.0);
}

What makes even less sense is that, not using the function and directly doing clamp(0.75, 0.0, 1.0) results in different broken behaviour (also a NaN but it doesn't spread over the entire screen anymore)

vec3 torchBlockSpecialLightColor = mix(vec3(2.0, 0.87, 0.27), fireSpecialLightColor, clamp(0.75, 0.0, 1.0));  //this is broken

This makes precisely zero sense as clamp01 is just clamp(x , 0.0, 1.0) so there should be absolutely no difference between the two.


Emin suspects this is some driver optimization going wrong, and clamp01 makes the driver scared to apply the optimization as its a custom function. Gri573 added they think it might be an error in constant folding

[djmrFunnyMan]

The clamp01 workaround is obviously unsatisfactory because it shouldn't be needed and it makes no sense. We have no idea why it changes anything at all. Something is clearly going very wrong and resulting in completely undefined behaviour.

[karen_intel]

Hey @djmrFunnyMan welcome to this forum and thank you for your post.

I can see your post was made in IGCIT forum as well.

I will be closing the thread there as this is the right forum for the type of issue you're reporting.

As this is an issue with a mod of the game, can you reroute the mod developer to this post?

We need direct contact with them to collaborate as we need to isolate the issue in a homebrew code (raw code focusing on the issue) to do some testing on our end with the code, debug, root cause the issue and report it internally.

Please let us know if the developer can proceed with this approach and is willing to collaborate.

Thank you

Karen

[djmrFunnyMan]

Okay for now let's focus on Issue #1. Issues 2 & 3 concern different developers. I will contact the relevant developer and ask them about it.

I suppose I shouldn't have bunched up 3 different issues in 1 report. Should I separate them?

[karen_intel]

Hey @djmrFunnyMan please do.

We will handle them all so having everything organized is better

We will be happy to collaborate, thanks for replying so quickly 

I'll be on the lookout

Karen

[djmrFunnyMan · Accepted solution]

I have separated the issues

https://community.intel.com/t5/Developing-Games-on-Intel/Frame-presentation-extremely-erratic-in-Minecraft-with-the/m-p/1665020#M2576

https://community.intel.com/t5/Developing-Games-on-Intel/OpenGL-mix-function-not-working-correctly-with-Minecraft-shaders/m-p/1665023#M2577

https://community.intel.com/t5/Developing-Games-on-Intel/OpenGL-procedurally-generated-night-nebula-shader-malfunctioning/m-p/1665025#M2578

No reponse from the mod developers for now