Procedural intersections

[TheDuckCow]

The initial scope of the intersection support is going to be using pre-generated scenes/objects. That's a good first step, but we eventually want to have procedural intersections. This task is to represent this work.

[TheDuckCow]

While we are not tackling this just yet, I did come across this video noting that at 15:42 it shows some nice details of the basis of intersection generation:

Transcribing and extrapolating with my understanding:

• They need enough space (lead in) to round the corners
• Need to support the width of the roads entering
• In between, you create "fillets" which create the rounding of the edges between the sides.
• And then fill with some geometry in the middle:
  • Probably varies a lot per kind of intersection, but in the example shown it looks like extrapolating a rectangle from opposite sides (for 4-way), for 3-ways can be a bit different but still a consistent breakdown of triangles
• Need to specify limits of range of angles for the roads to connect
• No input here around how the textures are generated, and I take it they are baking them to road-specific files, which is not really what we want to be doing. So this part remains to solve!

[TheDuckCow]

Thanks to Kitten on our team, here's at least one example of someone talking about how to approach procedural intersections. I think in the end we'll use a composite of techniques, but getting all the references we can is a solid start

https://twitter.com/noio_games/status/1704891239244382240

[TheDuckCow]

Another demonstration of an approach as well as user visual interaction: https://www.youtube.com/watch?v=3O897gbyiBk

This one is interesting, as the actual intersection is much more implied for the user, rather than it being an explicit object type. They seem to have a singular (equivalent) concept of RoadPoint. The icky party is that it means you end up creating multiple overlapping RoadPoints which still belong to each segments. But it's interesting it gives you some chance to wiggle-connect.

Two other videos I want to read more into: intersection decals and this Houdini intersection solver. This last one gives some nice philosphy for how to think of the curves connecting the segments.

[TheDuckCow]

Another video I came across for Unreal for creating intersections using a more primitive approach, this one's interesting in a way because it's just making use of overlapping roads and then overriding the material at the end. Their process:

1. Create the road going through
2. Over-connect the roads to each other
3. Create an "override" material for the specific sections being added (hm, a concept like this could be nice for RoadPoints too)
4. The using decals they are then able to add lines back to the correct edges of the mesh

https://youtu.be/RCv3dFUjOf0?si=T9_Jh0wzFTuYDeqZ&t=760

I don't think the above is exactly what we'd want to do, but the approach of using layered materials to get the right edges could be interesting. It depends on a global detail texture being used, which is also something we would probably want to implement eventually anyways.

[TheDuckCow]

Another example asset/system, another video. See here this time a blender addon called "Next Street" that does quite a lot.

• A vertex is our equivalent to a RoadPoint, edges are the actual streets
• The simplicity of creating intersections is hard to beat: extrude out from vertex from an existing point
• It works such that you can change the weight for how much it creases in or out of this point
• It has various preset profiles for the streets, e.g. with or without the sidewalk, barricades etc. I'm not sure if it has a way to do it for one edge at a time or if it's universal. A lot of the selling point here are all the assets it contains including: trees, benches (multiple kinds, lamppost, railings), trash cans; also with settings for the spacing of each of these too
  • This further more makes me think it would be helpful to define some kind of resource slot for RoadContainers which define the "style" of road, and this resource could itself contain arrays to elements and numbers of references. This way it's also easy to copy or even save to disk to quickly change the style of an entire city, while still giving you the option to change the style of single edges at a time.
• It DOES offer the ability to change the number of lanes, presets of 2, 4, 6 etc. And that is based on selecting single edges at a time. Not sure what it'd do for transitions between two lane counts without an intersection.
• Doe shave AI lanes for traffic, including through intersection