OpenGL: Clearcoat has no effect if BaseMaterial3D roughness is exactly 0

[Calinou]

• Related to BaseMaterial3D clearcoat rendering is broken with material roughness set to 0.0 in Forward+/Mobile #95207.

Godot version

4.2.beta1

System information

Fedora 38, GeForce RTX 4090 (NVIDIA 535.104.05)

Issue description

When using the Compatibility rendering method, Clearcoat has no effect if BaseMaterial3D roughness is exactly 0:

However, it works if roughness is set to 0.01 or 1.0:

Roughness 0.01	Roughness 1.0

This issue only occurs in Compatibility, not Forward+ or Mobile. I noticed it while working on a solution for #69327.

Steps to reproduce

• Add a MeshInstance3D and DirectionalLight3D (so that clearcoat can be seen).
• Assign a BaseMaterial3D to the MeshInstance3D, with Roughness set to exactly 0.0 and enable Clearcoat.

Minimal reproduction project

Clearcoat_Test_2.zip

[clayjohn]

See:

godot/servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl

Line 187 in 51f81e1

if (roughness > 0.0) { // FIXME: roughness == 0 should not disable specular light entirely