HDR 2D affects 3D glow and BCS

[allenwp]

Tested versions

Reproducible in v4.4.1.stable.official [49a5bc7]

System information

Godot v4.4.1.stable - Windows 11 (build 26100) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 980 Ti (NVIDIA; 32.0.15.6109) - 13th Gen Intel(R) Core(TM) i7-13700K (24 threads)

Issue description

Edit: Originally I included color correction in this bug report, but have removed it and created a separate issue for this specific case.

Turning on and off the rendering/viewport/hdr_2d project setting affects the appearance of 3D scenes that make use of the Glow and BCS (Brightness, Contrast, Saturation) effects.

Environment Effect	HDR 2D Disabled	HDR 2D Enabled
Glow (Additive)
Contrast and Saturation

Steps to reproduce

1. Set up a 3D scene with Glow or BCS (Brightness, Contrast, Saturation) effects.
2. Turn on and off the rendering/viewport/hdr_2d project setting and note that the appearance of the 3D scene changes.

Note: If using the Glow effect, the issue will only occur with Additive, Screen, and Softlight blend modes.

Minimal reproduction project (MRP)

hdr-2d-affects-3d.zip

Proposed Solution(s)

If I were to re-write the Vulkan rendering methods I would have them to be something like this, which resolves this issue but changes the appearance of these Environment effects for some configurations:

Work-in-progress branch: https://github.com/allenwp/godot/tree/vulkan-linear-bcs-glow

Note: It is necessary to change the appearance in some configurations to fix this bug.

I'm still digging into exactly how these changes should be made to be future-proof with support for #94496 in mind. This work-in-progress branch is based off of the existing PR #106962.

[clayjohn]

When HDR2D is off, these effects are all blended in sRGB space. When HDR2D is on, these effects are blended in linear space.

I think moving glow to linear space is probably a change we can make. But for adjustments, I think we are just going to have to document the difference and live with it. I don't think it is possible, or even desirable to try to make them behave the same when HDR2D is on and off.

Ultimately, we need to do a better job at communicating the fact that games need to be designed with HDR2D in mind. It isn't a setting that should be flipped on and off at run time, or for different users. Your art pipeline needs to consider it, so it should be a fixed decision from a project point of view

[allenwp]

Although brightness, contrast, and saturation are entirely subjective and can be performed in either linear or sRGB encoding (if ignoring the impact on future HDR output), both banding (dithering) and color correction effects were designed to be applied on sRGB encoded values and are incorrect when applied to linear encoded values (when HDR 2D is enabled). The middle screenshot shows this issue.

Edit: I've removed references to Color Correction from this report and created a separate issue instead: #107730

[allenwp]

I prefer to not change behaviour in any way (logic, visuals, etc.) unless there is a very strong reason to do so or it is a major release (i.e. 5.0). For this reason, I do not think it is a good idea right now with the current state of Godot to change the behaviour of Glow, BCS, and HDR 2D when many projects have been tuned to the specific existing behaviour.

But in relation to the 5.0 release and HDR output support, I believe there is value in having a clear understanding of what is correct and desirable behaviour and what is not.

But for adjustments, I think we are just going to have to document the difference and live with it. I don't think it is possible, or even desirable to try to make them behave the same when HDR2D is on and off.

Considering the framing for discussion I just shared, I am confused by why it would not be possible or even desirable to make them behave the same when HDR2D is on and off. Isn’t this simply a mater of ordering in the tonemapping shader?

Ultimately, we need to do a better job at communicating the fact that games need to be designed with HDR2D in mind. It isn't a setting that should be flipped on and off at run time, or for different users. Your art pipeline needs to consider it, so it should be a fixed decision from a project point of view

I’m not sure if this is true for the upcoming HDR output PR: I expect that most users who are developing a 3D game would want to have HDR 2D disabled for SDR version of their game for performance reasons and also allow players to optionally enable HDR output support. In this scenario, the difference in 3D Adjustments behaviour makes it difficult to author the game. Or is there no performance benefit to having HDR 2D disabled? Or maybe it’s impractical to support both modes in one game because 2D GUI stuff of a 3D game will be very different, even though no Adjustments were applied?

I get the feeling that there might be some major fundamental things that I don’t quite understand? This is something that I would like to get a good understanding of, especially in relation to HDR output, tonemapping, effects, etc. I’m happy to discuss here or have a voice call or chat during the rendering meeting if that’s easier.