unshaded mesh is brighter than albedo set in fragment shader with vulkan renderer

[jmdejong]

Godot version

v4.0.beta10.official.d0398f62f

System information

archlinux; vulkan on dedicated NVIDIA GeForce RTX 3060 Laptop GPU; opengl3 on integrated AMD Radeon Graphics (renoir, LLVM 14.0.6, DRM 3.49, 6.1.1-arch1-1)

Issue description

When using the fragment shader to set an albedo then the color that is rendered much too bright, even when the mesh is unshaded.
This happens with the vulkan renderer, but it does not seem to happen with the opengl3 renderer.

With vulkan renderer :

With the opengl3 renderer this does not occur:

(The lack of interpolation seems to be a different problem)

Used texture:

Shader:

render_mode world_vertex_coords, unshaded;

uniform sampler2D tex;

void fragment() {
	ALBEDO = texture(tex, UV).xyz;
}

This example uses the render mode unshaded for simplicity, but when lightning calculations do occur then this shader still shows a brighter color than expected

Steps to reproduce

View a mesh that uses the shader above and is given a texture as parameter in a project with the vulkan renderer

Minimal reproduction project

texturebrightness.zip

[jmdejong]

I just found out that this does not seem to be related to textures: setting the albedo to vec3(0.0, 0.5, 0.0) will result in the mesh having color #00bc00 in the vulkan renderer. With the opengl3 renderer it is #008000, which I would expect.

[Calinou]

This is likely a sRGB-to-linear conversion issue.

You can fix this by adding : source_color; as a hint to the texture uniform: uniform sampler2D tex : source_color;

[jmdejong]

Yes, adding that fixed the difference in color

[jmdejong]

When setting the albedo without a texture there is still a difference in color.

The left square is a standardmaterial that is unshaded and has albedo #008000 while the right square is from a shader that sets the albedo to vec3(0.0, 0.5, 0.0). On the opengl3 backend both squares are the same color, but on vulkan the right one is brighter.

Is this something that can be fixed? Or should it be documented and accepted? (for me it was not yet clear from the documentation that this could happen)

used shader:

render_mode unshaded;

void fragment() {
	ALBEDO = vec3(0.0, 0.5, 0.0);
}

Minimal reproduction project:
albedobrightness.zip

[clayjohn]

This isn't a bug, you are just forgetting the source_color hint when you set your uniform sampler2D See the docs for uniforms here:
https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/shading_language.html#uniforms

In the second MRP you are setting the quads to two different colors. The quad on the left is in sRGB space while the quad on the right is in linear space.

[kb173]

I hope it's okay to add something here because this issue was a top search result while debugging a similar problem I had:

Even with source_color or no custom shader (just a standard material with an Albedo texture), my texture appeared too bright in the editor. I set the material to unshaded and compared screenshots with the original texture to confirm that it was quite a bit too bright.

The reason was that Godot's viewport is set to the Filmic tonemap by default. It can be changed to Linear here:

I know this is intended, but I figured adding a comment here might help people with the same problem in the future.

[souplamp]

I know this is intended, but I figured adding a comment here might help people with the same problem in the future.

I am from the future. Thank you.

PS. If anyone is trying to use source_color (as mentioned above) in the VisualShader editor, make sure to go to your Texture2D node dropdown where it says "Data" and change it to "Color".