diff --git a/doc/classes/CompositorEffect.xml b/doc/classes/CompositorEffect.xml
index 76a38879188..9ac54edb11b 100644
--- a/doc/classes/CompositorEffect.xml
+++ b/doc/classes/CompositorEffect.xml
@@ -57,6 +57,17 @@
 			var render_scene_buffers : RenderSceneBuffersRD = render_data.get_render_scene_buffers()
 			var roughness_buffer = render_scene_buffers.get_texture("forward_clustered", "normal_roughness")
 			[/codeblock]
+			The raw normal and roughness buffer is stored in an optimized format, different than the one available in Spatial shaders. When sampling the buffer, a conversion function must be applied. Use this function, copied from [url=https://github.com/godotengine/godot/blob/da5f39889f155658cef7f7ec3cc1abb94e17d815/servers/rendering/renderer_rd/shaders/forward_clustered/scene_forward_clustered_inc.glsl#L334-L341]here[/url]:
+			[codeblock]
+			vec4 normal_roughness_compatibility(vec4 p_normal_roughness) {
+			    float roughness = p_normal_roughness.w;
+			    if (roughness > 0.5) {
+			        roughness = 1.0 - roughness;
+			    }
+			    roughness /= (127.0 / 255.0);
+			    return vec4(normalize(p_normal_roughness.xyz * 2.0 - 1.0) * 0.5 + 0.5, roughness);
+			}
+			[/codeblock]
 		</member>
 		<member name="needs_separate_specular" type="bool" setter="set_needs_separate_specular" getter="get_needs_separate_specular">
 			If [code]true[/code] this triggers specular data being rendered to a separate buffer and combined after effects have been applied, only applicable for the Forward+ renderer.