Implement AgX as a tonemapper

[ettiSurreal]

Very recently, Blender added Eary's AgX (improved version over the original config, if we do implement AgX into Godot, I think this should be the version to implement: https://github.com/EaryChow/AgX) as a new view transform in it's color management.

In Godot there are currently 4 options: Linear, Reinhard, Filmic and ACES. Unfortunately all of these have their issues. Reinhard and Filmic suffer from problems like the notorious six (#6096) and ACES is... problematic to say the least.
AgX fixes the issues Filmic had, and is all around a great tonemapper.

Godot doesn't utilize OCIO, so I don't know how one could implement a new tonemapper, but this discussion isn't about bringing OCIO support to the engine.

Related:
#7263

[Calinou]

Given the complexity of the OCIO file, this likely requires baking a LUT and using that LUT during tonemapping, which has the same binary size concerns mentioned in #7263.

This would steer me towards implementing a Custom tonemapping mode which allows you to specify your own 3D LUT to be used before color correction (and before tonemapping). LUTs for tonemapping can then be provided on the asset library.

[s-ilent]

I think that makes a lot of sense, but I'm worried a full implementation of OCIO and pipeline for importing them as LUTs might be very heavy duty for a lot of Godot users. As Blender has moved to use AgX as a default (through an OCIO profile, to be fair), I think it's also worth considering adding in an option for minimal AgX as an inbuilt tonemapper option for Godot for easy Blender parity.

https://iolite-engine.com/blog_posts/minimal_agx_implementation

[Calinou]

Thanks to the code you linked, I have a working proof of concept with AGX and AGX Punchy: https://github.com/Calinou/godot/tree/tonemap-add-agx

Testing project: tonemap_color_correction.zip

However, I'm not sure how the whitepoint property is supposed to be implemented. The blog post doesn't mention it, and any other references seem to imply the use of OpenColorIO or a standard D65 whitepoint (while we want to be able to adjust it here).

Also, if I want to open a PR, I'll have to contact the author to use the code under the MIT license (since the blog post or Shadertoy don't mention a license).

Preview

Linear

Filmic

ACES

AGX

Whitepoint is ignored here.

AGX Punchy

Whitepoint is ignored here.

[Calinou]

Pull request opened: godotengine/godot#87260

[statixVFX]

+1 for AgX support.

It solves a very important problem in computer graphics when it comes to color reproduction with high saturation (the collapsing 6 colours)

AgX vs rec709 (which has the same 6 collapsing colours as srgb, filmic srgb and aces)

[redhoot-dev]

+1 for AgX, its been phenomenal in Blender and other places.

It solves the problem described above of the collapsing 6 colors witch have plagued computer graphics for ages.

Look at any modern AAA game, and you still see colors skew harshly towards yellow, magenta when over-exposing.
This is very evident in areas of high contrast, like weapon-shot lighting, FX, impacts or just harsh lighting.