Preview resolution value for curves to alleviate performance issues of long curves

[AyyZerrAsa]

Fixes #81707
Curves now preview in editor with a fixed resolution per curve section that can be defined by the user. This helps avoid the issue with long curves producing a very large amount of primitives/draw items, which decrease the responsiveness of editing path3d/path2d curves.

• Closed-curve support Add closed property to Curve3D #86195

Godot.Path3d.Fix_2.mp4

[AyyZerrAsa]

Would be best to wait for this change before attempting a merge #86195

[AyyZerrAsa]

Unsure why the unit test is failing with logged: Unnamed argument in position 0 of method 'Curve2D.set_preview_resolution'.
Also checked with #86195 and a change will definitely need to be made to support the closed curve logic.

[AThousandShips]

You need to add the argument to the bind:

ClassDB::bind_method(D_METHOD("set_preview_resolution", "resolution"), &Curve2D::set_preview_resolution);

[Calinou]

Tested locally (rebased on top of master 739019e), it works as expected.

path_3d_detail_settings.mp4

One concern I have though is that the debug_preview_resolution property is part of the Curve2D/Curve3D resource, while I think it should be part of the Path2D/Path3D node, like #82321 does for its debug color property. The resource does not have any visual representation of its own, so a subdivision count property feels out of place (and may be confused with the existing Bake Resolution).

[Mickeon]

I don't see the point in not having this as an editor setting, instead.

[Calinou]

I don't see the point in not having this as an editor setting, instead.

You may need per-path adjustments to ensure performance remains good in the editor (while preserving as much detail as possible), as some paths can be very long and complex while others can be shorter.

[AThousandShips]

Suggested change

	real_t offset;
	point == 0 ? offset = 0 : offset = c->get_baked_distance_at_point(point);
	real_t offset = point == 0 ? 0 : c->get_baked_distance_at_point(point);

Don't use assignment inside a ternary

[AThousandShips]

Suggested change

	real_t offset;
	point == 0 ? offset = 0 : offset = curve->get_baked_distance_at_point(point);
	real_t offset = point == 0 ? 0 : curve->get_baked_distance_at_point(point);

[kleonc]

@AyyZerrAsa Are you planning to apply suggestions / improve this PR?

What I don't like about this PR is that no matter how short given path segment is, it would still draw all debug_preview_resolution fishbones for it. It might make sense to add some lower bound for the sampling interval length.

Also another missing optimization/simplification is using only a single segment for path segments with relevant out/in zero vectors (they're straight line segments, no need to subdive them).

+I support godotengine/godot-proposals#9459, disabling the fishbones/arrows drawing should be possible one way or another (whether by a project setting, or per Path2D/3D property (like the one being added in this PR)).