Vulkan: Emit a node configuration warning when GeometryInstance3D fade is enabled, but the margin is set to 0

[Calinou]

Related to #55367.

Godot version

4.0.dev (5efe80f)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

The transparency-based distance fade implemented in #54222 doesn't seem to work as expected, both on opaque and transparent (alpha blended) materials.

From left to right:

• Opaque material, no LOD
• Opaque material, standard LOD (no fade)
• Opaque material, LOD with Self fade
• Opaque material, LOD with Dependencies fade
• Transparent material, LOD with Self fade
• Transparent material, LOD with Dependencies fade

Spheres on the top have Transparency set to 0.2, spheres on the bottom have Transparency set to 0.0.

visibility-range-fade.mp4

Steps to reproduce

• Add a MeshInstance3D node.
• Configure a LOD distance on the MeshInstance3D in Visibility Range > End.
• Set the fade mode to Self.
• Move away and notice that the mesh still fades in and out instantly. This occurs both if the mesh has an opaque or transparent material.

Minimal reproduction project

test_visibility_range_fade.zip

[Calinou]

It's due to a configuration mistake on my side. You need to set the Visibility Range End Margin (which normally acts as hysteresis) to a value greater than 0.0 for the fading effect to be visible.