Sample sky and reflection probe texture in shader

Help Shaders
1

Godot Version

v4.2.2.stable.official [15073afe3]

Question

Lowering roughness and increasing metallic on the standard material makes the surface reflect the sky or use the nearest reflection probe. How do I sample the sky / reflection probe texture in my own shader?

1 Like
2

You can always export a material you have edited into shader code to see how it works.

3

When I convert that material to a shader this is what I get:

void fragment() {
	vec2 base_uv = UV;
	vec4 albedo_tex = texture(texture_albedo,base_uv);
	ALBEDO = albedo.rgb * albedo_tex.rgb;
	float metallic_tex = dot(texture(texture_metallic,base_uv),metallic_texture_channel);
	METALLIC = metallic_tex * metallic;
	vec4 roughness_texture_channel = vec4(1.0,0.0,0.0,0.0);
	float roughness_tex = dot(texture(texture_roughness,base_uv),roughness_texture_channel);
	ROUGHNESS = roughness_tex * roughness;
	SPECULAR = specular;
}

This fragment shader code doesn’t sample the sky texture, it just sets roughness and metallic, and yet the sky is still reflected. I need a way to sample that same sky texture.

4

I think this can be done by messing with RADIANCE and IRRADIANCE. (I was looking at the sky shader doc, and it talks about radiance cubemap)

Also ambient_light_disabled render mode could be a quick test to see if it turns off the sky environment.

If those aren’t enough and ambient_light_disabled can turn of the reflection, I think you could then sample your own texture and set the radiance color to the texture sample.

5

RADIANCE doesn’t seem to be what I need, as it isn’t set to anything by default (it’s zero)
Sorry for not explaining very well, but this is what I’m talking about:
image

These meshes are using StandardMaterial3D with Roughness set to 0 and Metallic set to 1. You can see they reflect the sky, and if you add a reflection probe they can reflect the surrounding environment as well. This is the texture I’m trying to access - the reflection, so I can sample and use it myself.

6

As far as the docs go it isn’t available to sample from.

It’s seems like the environment and probes are backed into cubemap for metallic reflection.

Note:

The RADIANCE variable is an out only, and it will blend the color with whatever the current environment is based on the alpha you set.

7

There is also samplerCube type for shaders, maybe you could setup your own cubemap to sample from.