Shrinkwrap roads to terrain

[TheDuckCow]

Already being asked for by a few people, eventually it would be nice if we have a way to shrinkwrap the road to a terrain.

We need to think this feature out some more, but ideas so-far on requirements:

• Must be able to project onto already set up collission meshes
• Must be optional, likely default off for performance. Could make sense to make this be a per RoadPoint setting (so that you could disable or enable it only for relevant stretches)
  • This could pair with a toggle on the RoadContainer which sets/unsets for all RoadPoints within the container. This is instead of it being a RoadContainer-level setting
• Should have a max distance param, which defines the maximum amount down-wards the road should be projected (so it doesn't try to go into deep ravines/consider bridges). Ideally some smoothing between loop cuts that are floating from those on the ground
• Should have a max "angle" which basically says how steeply the road is allowed to change due to shrinkwrapping. This way a small but very deep crevice only makes a subtle difference, instead of the whole road sinking down for just one loop cut.

Technical ideation:

• Projection could work in a number of ways:
  • Per vertex point projection: Will be a bumpy road for sure! And the most expensive to compute. We could probably do some smoothing based on the distance of the gutter profile height, to make it a bit less wobbly
  • 2 or 3-point leveling: basically instead of per vertex, compute the height to the left and right of a given edge loop of the road, and possibly a point in the middle. So cross sections are still mostly smooth, but still roughly conforming to the road. Paired with a high-enough gutter profile, this likely could work for most terrains for expected results (if the terrain is so bumpy this doesn't work, it probably realistically needs to be smoothed anyways)
• Raycasting: will be expensive, might be able to use threads for some of this, maybe creating a lookup dict or something. We should also assume that the raycast will be emitted from somewhere well above

Expecting this would be a v1.0+ (ie Godot 4 only) feature.

[dev-bre]

is this going to allow the road to adjust itself to the terrain shape? I see that similar tools in unity and UE allow also the other way round.. the road changes the shape of the terrain below (raising the terrain to fill the space).

[TokisanGames]

For Terrain3D you can require the user to enable our full terrain collision in the editor. Or you can just detect if we're installed and query heights directly. https://terrain3d.readthedocs.io/en/latest/docs/integrating.html.

As for using raycasts to place your roads, running thousands of raycasts once in the editor, even if it takes a few seconds after a button push is not a concern.

[TheDuckCow]

Thanks for sharing the ideas! For sure @TokisanGames I'll be giving this a try once we wrap up/have a first stable godot 4 version. I definitely have the intention of integrating smoothly with as many terrain editors as is realistically feasible.

@dev-bre yup that is a common feature as well, but it the terrain engine itself needs to provide a way to do this. With at least one terrain dev I spoke with, they have a feature to input curves/paths which are used to define areas to smooth out and level the terrain. So as long as we can feed in the road generator's underlying curves through an appropriate callback, we'd be in good shape.