mesh object will not affected by the Light with specific values Material settings

[snougo]

Godot version

3.3.3 and 3.4 beta5

System information

macOS 10.14.6 intelGPU GLES3 and GLES2

Issue description

When setting Spatial Material with value 1 Metallic and value 0 Roughness, Mesh Object will not affected by the Light. both in GLES3 and GLES2

in blender with value 1 Metallic and value 0 Roughness

Screen.Recording.2021-09-25.at.1.14.47.AM.mov

in Godot with value 1 Metallic and value 0 Roughness

Screen.Recording.2021-09-25.at.1.15.16.AM.mov

Steps to reproduce

see Minimal reproduction project

Minimal reproduction project

bug report.zip

[clayjohn]

@Calinou The specular blob calculation is skipped if roughness is 0.0

godot/drivers/gles3/shaders/scene.glsl

Line 1122 in c265474

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

You can see that, while this was partially intended, the original author didn't think it was correct (hence the comment).

[Calinou]

@clayjohn I see, I was referring to this particular bit in 3.x's GLES3 shader code:

godot/drivers/gles3/shaders/scene.glsl

Line 2212 in c265474

diffuse_light *= 1.0 - metallic; // TODO: avoid all diffuse and ambient light calculations when metallic == 1 up to this point

In master, the same line exists but it doesn't have a comment:

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

Line 1877 in 53306cb

diffuse_light *= 1.0 - metallic;

[clayjohn]

@Calinou Remember that there are 2 primary sources of light, diffuse light and specular light. Metallic surfaces don't have any diffuse light, it is all specular. The code you link is what ensures that there is no diffuse light for metallic materials.

The issue OP posted about is a missing specular blob when compared to Blender.