Global shader uniform color not equal to regular uniform color.

[OlivierVanHoutte]

Godot version

4.0.beta10

System information

Windows 10 Vulkan

Issue description

The shader global color (top left) is the same hex code as the shader uniform (bottom right). But If i create an unshaded sphere, and show the colors next to each other, the shader global color is slightly lighter than the shader uniform color.

I thought maybe it's because of my shader code, so I reduced it to as simple as possible.

Steps to reproduce

Create an empty project.
Add a new shader global color.

Create a new shader material.
Set rendermode to unshaded.
Set the ALBEDO to the shader global color

Create an exact replica of this shader, but set the albedo to a regular shader uniform color.

Make sure both colors have the exacts same hex code.

Minimal reproduction project

test2.zip

[clayjohn]

This may end up being something that is a documented limitation. Right now, you hint to Godot what the source of the uniform is - in this case the source is a color. Godot then decides whether to convert it from sRGB to linear depending on the destination. Spatial shaders convert to linear as lighting happens in linear space. CanvasItem shaders don't convert to linear as 2D rendering happens in sRGB space.

Global uniforms can be used in either, but they map onto the same uniform internally, so they have to be either sRGB or linear in both Spatial shaders and CanvasItem shaders.

My preference would be for global uniforms to always convert to linear when source_color is used (i.e. matching the behaviour in spatial shaders). That way users still have the power to use either linear or sRGB.

[OlivierVanHoutte]

So a temp fix would be gamma correction by raising your color to pow 2.2 like below.
I like your proposal of making it linear when source_color is used.

[clayjohn]

The more exact formula is

ALBEDO = mix(pow((col.rgb + vec3(0.055)) * (1.0 / (1.0 + 0.055)), vec3(2.4)), col.rgb * (1.0 / 12.92), lessThan(col.rgb, vec3(0.04045)));

[huwpascoe]

This may be fixed now #101642

[clayjohn]

This may be fixed now #101642

I don't think so. The global buffer is uploaded in a different function.

See

godot/servers/rendering/renderer_rd/storage_rd/material_storage.cpp

Line 1866 in c394eaa

_fill_std140_variant_ubo_value(datatype, 0, p_value, (uint8_t *)&global_shader_uniforms.buffer_values[pos], true); //instances always use linear color in this renderer

[akien-mga]

I tested and the MRP still shows the issue in current master (80096e9).