(wip) feat: Instancer LOD

[laurentsenta]

Introduce four levels of LODs for multimesh instance

See thread in Discord

Task list:

• Decide on using an array or hardcoded floats for the distances
• Actually use the LOD'd mesh in the instancer
• Shadow LOD
• figure out the visibility margin thingy
• Fix the "everything resets on loading" issue
• Remove visibility range, and figure out upgrade path
• Field validation
• Update
• Cleanup
• Shadow min / max config
• Field validation (bis)
• Update the doc
• Also update the notes on "in the future we'll chunk MMIs" this is already implemented

Regarding validation:

This PR introduces a bunch of fields that are related to each other:

• maximum lod value is valid if the scene is loaded and must be less than mesh count
• maximum shadow lod is valid if <= maximum lod and >= minimum shadow lod (and vice versa for minimum shadow lod)
• Cast Shadows validity depends on the shadow lods:
  • if cast shadow is double-sided or shadows only, it will interact weirdly with min/max shadow lods

Checking values in the setters will be super annoying to use, as in "I'm trying to lower the maximum lod, but nothing happens" > "yes, you need to lower the minimum shadow lod first".

This is a perfect use case for configuration warning, which is a work in progress:

• [4.4] Configuration warnings may change implementation #321
• Rework the Configuration Warning system godotengine/godot#90049

[laurentsenta]

Need maintainer input: should we deal with the upgrade from visibility_range to _lod_visibility_ranges[0]? how?

[TokisanGames]

Yes.

• Leave the old variable.

• Change the setter to call the new setter.

• Move both to the bottom of the file headed with a comment: //DEPRECATED 1.0 - Remove 1.1

• Remove the getter.

• _bind_methods(): Move the bound variables/functions to the bottom and add the comment.

• _bind_methods(): change the property usage to no_editor so it doesn't show in the inspector, eg.
  ADD_PROPERTY(PropertyInfo(Variant::ARRAY, "region_offsets", PROPERTY_HINT_ARRAY_TYPE, vformat("%tex_size/%tex_size:%tex_size", Variant::VECTOR2, PROPERTY_HINT_NONE), PROPERTY_USAGE_NO_EDITOR), "set_region_offsets", "get_region_offsets");

• In the XML docs note it is deprecated and to see the new function.

[laurentsenta]

Done in 33a46e3

[laurentsenta]

Need maintainer input: every time I reopen the project, the maximum lod and shadow lod values are reset to -1,
I think this is because the mesh is not loaded when the editor tries to set the instance's value.

If you change the values and then close and reopen the scene, that'll work.

Is there an idiomatic way to avoid this?

[TokisanGames]

When Godot loads the scene file it loads all settings from the scene file. You don't really know which one it will load first. If this is loaded before the scene, get_mesh_count() will be zero, which sets your _maximum_lod = -1.

If packed_scene.is_null() then you shouldn't check get_mesh_count() and accept the value as it is. It won't be used while the scene is null.

When packed_scene is loaded, you can verify that maximum_lod is valid. Same w/ shadow lod.

[laurentsenta]

Done in fcaccb9