Clearcoat improvements and fixes

[LiveTrower]

Currently, the implementation of Godot's clearcoat is broken as it doesn't correctly reflect the sky and doesn't take the reflection probe's reflections into account, resulting in the clearcoat effect being almost nonexistent.

Improvements and Fixes

• Now, 1.0−F is applied to implement energy conservation.
• The sky reflections have been fixed.
• The clearcoat now takes the reflection probes into account.
• An approximation of iorTof0(f0ToIor(f0),1.5) is now applied.

The following table shows the before and after.

Before	After

⚠️ Important Notes ⚠️

• I'm not sure if I'm applying the energy conserving (1.0−F) correctly, so this should be taken with a grain of salt.
• I removed the horizon specular occlusion from the clearcoat since, in my opinion, there isn't a very noticeable difference and also to make it a bit cheaper, but if someone argues that it's necessary, I can bring it back.
• For compatibility, since the IBL (Image-Based Lighting) isn't applied to the clearcoat, I left it as is because I don't know if this is intentional due to performance concerns.
• I wonder if it would be a good idea to also apply specular antialiasing to the clearcoat.
• This PR is important for the integration of sheen shading.

[fire]

diff --git a/drivers/gles3/shaders/scene.glsl b/drivers/gles3/shaders/scene.glsl
index a4e61e8..bd98ee1 100644
--- a/drivers/gles3/shaders/scene.glsl
+++ b/drivers/gles3/shaders/scene.glsl
@@ -1551,17 +1551,17 @@ void light_compute(vec3 N, vec3 L, vec3 V, float A, vec3 light_color, bool is_di
 #endif
 
 #if defined(LIGHT_CLEARCOAT_USED)
-		// Clearcoat ignores normal_map, use vertex normal instead
-		float ccNdotH = clamp(A + dot(vertex_normal, H), 0.0, 1.0);
-		float cLdotH5 = SchlickFresnel(cLdotH);
+	// Clearcoat ignores normal_map, use vertex normal instead
+	float ccNdotH = clamp(A + dot(vertex_normal, H), 0.0, 1.0);
+	float cLdotH5 = SchlickFresnel(cLdotH);
 
-		float Dr = D_GGX(ccNdotH, mix(0.001, 0.1, clearcoat_roughness));
-		float Gr = V_Kelemen(cLdotH);
-		float Fr = mix(0.04, 1.0, cLdotH5) * clearcoat;
-		cc_attenuation = 1.0 - Fr;
-		float clearcoat_specular_brdf_NL = clearcoat * Gr * Fr * Dr * cNdotL;
+	float Dr = D_GGX(ccNdotH, mix(0.001, 0.1, clearcoat_roughness));
+	float Gr = V_Kelemen(cLdotH);
+	float Fr = mix(0.04, 1.0, cLdotH5) * clearcoat;
+	cc_attenuation = 1.0 - Fr;
+	float clearcoat_specular_brdf_NL = clearcoat * Gr * Fr * Dr * cNdotL;
 
-		specular_light += clearcoat_specular_brdf_NL * light_color * attenuation * specular_amount;
+	specular_light += clearcoat_specular_brdf_NL * light_color * attenuation * specular_amount;
 #endif // LIGHT_CLEARCOAT_USED
 
 	if (metallic < 1.0) {

The github actions is complaining about formatting.

[LiveTrower]

@fire I'm having trouble with the CHANGELOG.md. The pre-commit hook is giving me this message: "CHANGELOG.md:1297: hidding ==> hiding, hidden." I assume it's because of a typo or spelling error.

[LiveTrower]

I already solved it.

[Calinou]

Tested locally, it works as expected in Forward+ and Compatibility.

In Mobile, I get a shader compilation error (and subsequent error spam) though: test_clearcoat_mobile.zip

Visual comparison in Forward+:

Type	Before	After
None
ReflectionProbe
SSR
ReflectionProbe + SSR

[LiveTrower]

In Mobile, I get a shader compilation error (and subsequent error spam) though: test_clearcoat_mobile.zip

On my end, it's not giving me any error. Could you please show me the error you're getting?