Hello!
It's a weird issue that I create here and I will try my best to explain it:
The SEUS RC6 shaders can be loaded on the latest optifine version, but they are totally broken and look like this:

Instead of this (screenshot taken in 1.4.7)

On Iris, the shader just looks like vanilla Minecraft.
So as you can see, water and moving leaves work. The problem is the shadows etc. I create this issue because this shader with Optifine was at the beginning not working at all, and over the years it became more and more compatible (water started working, no lines between chunks etc.) so I was wondering if it was possible to make this shader work again on modern versions of Minecraft.

This also applies to SEUS RC2 that had a "Revived" shaderpack made by robobo meant to be compatible with MC Optifine 1.8/1.9, but it's not working anymore since 1.17.1 and now looks like this (very similiar lightning issue)

Hope it's possible to make these shaders work again, I loved them!

It would help if you were able to (1) provide links to the relevant downloads for the versions you want to be compatible with Iris and (2) some steps to get a working configuration (ie, exact MC / OptiFine / ShadersMod / etc versions). Otherwise I just have to make guesses about how the working configuration works instead of being able to actually test what it's doing. Specifically, I'm having a hard time determining how the lighting colors ever worked in the first place - it doesn't seem to make sense.

Okay, so here is the download link (is available on the minecraftforum page, but I don't know if it's the exact one that I use, the author published previews versions on his facebook page etc., so I must test it) : http://www.mediafire.com/file/553aasegikj0qbo/SEUS_v10_RC6_shaderpack.zip/file
For the exact working configuration, I use: Minecraft 1.4.7, Optifine_1.4.6_HD_U_D5 (as jar mod), and ShadersMod-mc1.4.6-ofuD5-1.44 (as jar mod too, found here: https://mcarchive.net/mods/glslshaders?gvsn=)

At least on 1.16.5, it seems like the main issue is just this part of shaders.txt not being implemented:

uniform <type> gdepth;                          if (bufferFormat[1] == RGBA) bufferFormat[1] = RGBA32F;

As well as the legacy DRAWBUFFERS inferring not working either.

There's also issues due to gl_Vertex including the camera transformation, and everything seems to be pretty orange, perhaps due to needing a custom lightmap or something?

guys i could help you, older shaders works until 1.17.1 pre33 version. I have running Seus V10 RC6 with lightmap (because seus shaders of V10 RC1 to RC7 use lightmaps)

the other problem that older shaders doesn't work in newer versions is because there is a ";" at an #endif in the final.fsh

(final.fsh file of seus v10 rc6)

Just tested Seus RC6 from the minecraftforum thread and it does not work like the one I have, I don't think I have the right to give here publicly the shaderpack (including the modified RC2 version from robobo), how could I give you them privately ?

I suppose you could send them on discord, I don't believe that SE would have a problem with that being done privately if they've been lost from the public record over time.

Hello @ByCanche, would you be willing to share more details about the lightmap invovled? I'd be curious if you could link me to a copy of the lightmap or to more information on it.

@coderbot16 sure, it's updated to 1.19.x, change the pack format depending of the version you use
SEUS adjusted RC2.zip

HI,does anybody here? I really want to use this nostalgic shader in 1.19.3. But I have same problem with you.
I want to help each other.

@coderbot16 sure, it's updated to 1.19.x, change the pack format depending of the version you use
SEUS adjusted RC2.zip

You have adjusted resource pack for 1.19.x? So that means, older seus (RC2) may works in 1.19? If so, I'm really curious about it. I really want to play with nostalgic graphics.