CODEWITHSUNDEEP
c#unity-game-enginemeshconvex-hull
Jaded_Kronos
Jaded_Kronos

Reputation: 53

Creating Custom Convex Hull & Mesh in Unity

I'm currently trying to implement a complex search field into a unity project I'm working on, where a user has the ability to spawn points into a scene. My goal is to create a custom shape for that user based on the points they created, and then I'd like to detect whether or not other objects are inside that shape, similar to the detection of a point inside a complex hull (still shaky on the theory behind that, but an example can be found here). If possible, I'd also like the shape to update itself if the points are later moved, giving it an almost elastic, stretchy feel.

So far, every tutorial or resource I've found online does the exact same basic example, where a script assigns new verts, UVs and triangles to a custom mesh to make a plane using two triangles, but this is frustratingly simple, and decidedly unhelpful when I simply don't know what the final shape will look like, or what triangles to actually draw even when the user has as little as five points in the scene.

As of right now, the closest visual representation I could come up with has a List keep track of the user's points, and a script that just draws a bunch of pseudo-triangles using LineRenderers to connect every point, even ones that aren't exterior faces, by iterating through the List multiple times. While this looks close to what I want, it isn't actually useful in any way, as I don't know how to 'fill' those faces, and I'm still relatively lost when it comes to whether or not an object is inside that hull, like the red sphere shown in the example below.

Angle 1

Angle 2

I can also destroy and redraw those lines repeatedly during the Update() method, which allows me to grab a point and move it around, resulting in the shape dynamically changing, but this results in an undesirable flashing effect that I'd sooner avoid for now.

As this is such a broad question, I've also included the method I'm using to draw these lines below, which parents a bunch of lines shaped like triangles to an empty game object for easy destruction and recreation:

void drawHull()
{
    if (!GameObject.Find("hullHold"))
    {
        hullHold = new GameObject();
        hullHold.name = "hullHold";
    }

    foreach(GameObject point in points)
    {
        for (int i = points.IndexOf(point); i < points.Count - 2; i++)
        {
            lineEdge = Instantiate(lineReference);
            lineEdge.name = "Triangle" + i;
            lineEdge.GetComponent<LineRenderer>().startColor = Color.black;
            lineEdge.GetComponent<LineRenderer>().endColor = Color.black;
            lineEdge.GetComponent<LineRenderer>().positionCount = 3;
            lineEdge.GetComponent<LineRenderer>().SetPosition(0, points[points.IndexOf(point)].transform.position);
            lineEdge.GetComponent<LineRenderer>().SetPosition(1, points[i + 1].transform.position);
            lineEdge.GetComponent<LineRenderer>().SetPosition(2, points[i + 2].transform.position);
            lineEdge.GetComponent<LineRenderer>().loop = true;
            lineEdge.SetActive(true);
            lineEdge.transform.SetParent(hullHold.transform);
        }
    }
}

If anyone has encountered a similar problem somewhere else that I simply couldn't find, please let me know! Anything from more knowledge on creating a custom mesh to a more in depth and beginner-friendly explanation on determining if a point is inside a convex hull would be quite helpful. If it's at all relevant, I am working in VR and running version 2018.2.6f1 to ensure that the Oculus rift package and Unity play nice, but I haven't been having any issues working in an environment a few months behind.

Thanks!

Upvotes: 0

Views: 1767

Answers (1)

zambari
zambari

Reputation: 5035

You do mention assinging verts and tris to a mesh - this is the 'right' way to do it in unity, as it ties in with highly optimized MeshRenderer, and also I believe Colliders are able to use meshes where given the shapes like that, so you should be able to just plug into PhysX and query it for colliders overlaping with your mesh. Doing it by hand, aka iterating through faces and establishing actual bounds of your object is actually pretty hard to do effectively

Upvotes: 0

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