Texture height vertex displacement and mesh tessellation

[Xtarsia]

Closes #175

This went through many itterations, but is finally getting close.

Implements:

• Clipmap Mesh subdivision, upto 5 levels, for 32 vertices per meter.
• A Displacement Buffer via Veiwport, that renders 1 pixel per vertex, for each subdivision, upto the full 1m vertices.
• A debug view that renders the buffer in fragment.
• Per asset height offset and scale settings.
• Material option to disable / enable displacement (seperate from the tessellation level mesh setting)

Inclused some fixes:

• use propper TNB martix for world space texture normals. Previous version was wrong (needed transforming from view space)

Todo:

• Fix cleanup / crash on quit
• Probably need to check vertex spacing
• Disable more code when tessellation level is 0
• test mobile
• test web
• expose a buffer override shader
• move material (and override) fully to Terrain3DMaterial
• Docs

explore Including buffer in dynamic collision will be for a different PR.

[TokisanGames]

It works a lot better, and I intuitively get it now.

• Since MA/Displacement Offset does nothing unless scale is >0, scale should be listed first.
• The red/green view is usable, but I prefer to see the collision.
  • I considered if we should put it on a hotkey like 5, or if that hotkey could simultaneously change to displacement debug view, change to editor collision, and enable view gizmos. However, maybe just enabling editor collision is enough and better even than the debug view. 🤔 Either way, we've got to get rid of that region gizmo and start drawing the region boundaries in the shader only. Draw region grid in shader instead of gizmos #100

• We can and should update the displacement buffer when it's changed in the material. It's hard to see the effect in non-R/G view because moving the camera is jarring. This works to get the signal:

bool Terrain3DMaterial::_set(const StringName &p_name, const Variant &p_property) {
...
	if (p_name == StringName("displacement_sharpness")) {
		LOG(MESG, "displacement_sharpness: ", p_property);
	}

• Once I change the tessellation setting, or enable the displacement debug view, I get this error message once, 60-80% of the time when I run the game. It seems to be more often after I change tessellation or debug view:

ERROR: Method/function failed.
   at: get_dependencies (scene/resources/resource_format_text.cpp:1535)

• Can be rebased and conflicts addressed. Re-expose generated_type can be dropped.

---

That's my usage review. I'll look at the code and docs again a bit later.

Some notes for me:

• Recommended view: gizmos + editor collision, or displacement debug view, change to editor collision, and enable view gizmos
• Displacement Sharpness changes the buffer, and is only updated on camera movement - (but could be fixed)

[TokisanGames]

Why is the displacement buffer shader in the material? Maybe it makes more sense to put it in a subgroup in Mesh, enabled by tessellation? I anticipate the ocean mesh and ocean shader to be a separate group as well.

[Xtarsia]

Why is the displacement buffer shader in the material? Maybe it makes more sense to put it in a subgroup in Mesh, enabled by tessellation? I anticipate the ocean mesh and ocean shader to be a separate group as well.

Yeah, that does make sense actually.

[TokisanGames]

Displacement scale could remain in the material as is. Or it could be a private uniform in the shader, set by a setting combined with the other displacement settings. Then everything is in one place.

[Xtarsia]

Displacement scale could remain in the material as is. Or it could be a private uniform in the shader, set by a setting combined with the other displacement settings. Then everything is in one place.

Yeah the terrain shader displacement scale is a "global" scale that determines the maximum displacement distance.

Eg if set to 2 (meters) then the maximum extrusion, and depresion is 1m, for a total of 2m.

Making it private and moving to the mesh section as a part of a subgroup would make sense as well. (as well as adding some blurb about what I just said to the docs)

[Xtarsia]

Moved the override, and displacement scale into a subgroup under mesh. (not sure how I make it hide if tessellation == 0)

Added the sharpness property update. (it really is much better seeing it in real time)

Dropped the generated type commit.

Added the extra notes to the docs.

[TokisanGames]

not sure how I make it hide if tessellation == 0

_get_property_list()

See OOTA/Lod.gd for an example. Add a subgroup there.

[Xtarsia]

found out about _validate_property() after a bit of searching. Seems to do the trick nicley for this use case. (hiding the displacement group from the inspector)

updated docs a bit more to include your notes about displaying the collision mesh.

re-ordered displacement scale and offset.

moved the displacement scale inspector property from material to terrain3d as well.

Hopefully its ready now.

[TokisanGames]

Ok, looks good. I've adjusted the docs and parameter ordering.

The last remaining issue for this PR is Flat mode texturing is broken with the lightweight shader.

Please fix that, then you can merge in this PR.