2D中的Unity自定义形状生成对象

Question

I new to Unity. I'm trying to re-write game from the site in Unity http://www.boxcar2d.com/index.html

So I found that I should work with Sprites. Now I am trying to dynamically generate an arbitrarily shaped "car". I need it to collide and interact with physics and gravity. I tried to use Mesh but it seems like there is no way to turn Mesh into a Sprite and work with it like with physical object.

What kind of structures or approach should I use for creating those "cars" dynamically?

Here is my code so far if that somehow will be useful.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GenerateCar : MonoBehaviour {

    public Material mat;



    // Use this for initialization
    void Start()
    {
        Mesh mesh = new Mesh();

        Vector3[] vertices = new Vector3[6];

        vertices[0] = new Vector3(0, 0);
        vertices[1] = new Vector3(4, 1);
        vertices[2] = new Vector3(3, -1);
        vertices[3] = new Vector3(-1, -3);
        vertices[4] = new Vector3(3, -6);
        vertices[5] = new Vector3(0, 1);
        //vertices[6] = new Vector3(width, height);
        //vertices[7] = new Vector3(width, -height);

        mesh.vertices = vertices;

        mesh.triangles = new int[] { 0, 1, 2, 0, 2, 3, 0, 3, 4, 0, 4, 5, 0, 5, 1};

        GetComponent<MeshRenderer>().material = mat;

        GetComponent<MeshFilter>().mesh = mesh;
    }

}

Answer 1

If you need to make arbitrary shapes that can't be made with just horizontally and vertically stretching sprites you make ahead of time, then sprites aren't suitable. A Mesh would be more practical.

If you can describe the shape you want to make as a polygon with a known ordered list of points, you can use the community Triangular class to create a Mesh . There are other methods, but this is a community standby.

Whatever you use to make the Mesh , you will need to make sure there is also a PolygonCollider2D on the same object as the Mesh . You can use SetPath to create its outline using the same points as you fed into Triangulator . You will also need a Rigidbody2D to handle physics and collision for the body of the car. I've never worked with wheels but WheelJoint2D might be what you can use for the wheels.

Triangulator Usage Example

using UnityEngine;

public class PolygonTester : MonoBehaviour {
    void Start () {
        // Create Vector2 vertices
        Vector2[] vertices2D = new Vector2[] {
            new Vector2(0,0),
            new Vector2(0,50),
            new Vector2(50,50),
            new Vector2(50,100),
            new Vector2(0,100),
            new Vector2(0,150),
            new Vector2(150,150),
            new Vector2(150,100),
            new Vector2(100,100),
            new Vector2(100,50),
            new Vector2(150,50),
            new Vector2(150,0),
        };

        // Use the triangulator to get indices for creating triangles
        Triangulator tr = new Triangulator(vertices2D);
        int[] indices = tr.Triangulate();

        // Create the Vector3 vertices
        Vector3[] vertices = new Vector3[vertices2D.Length];
        for (int i=0; i<vertices.Length; i++) {
            vertices[i] = new Vector3(vertices2D[i].x, vertices2D[i].y, 0);
        }

        // Create the mesh
        Mesh msh = new Mesh();
        msh.vertices = vertices;
        msh.triangles = indices;
        msh.RecalculateNormals();
        msh.RecalculateBounds();

        // Set up game object with mesh;
        gameObject.AddComponent(typeof(MeshRenderer));
        MeshFilter filter = gameObject.AddComponent(typeof(MeshFilter)) as MeshFilter;
        filter.mesh = msh;
    }
}

Triangulator source

using UnityEngine;
using System.Collections.Generic;

public class Triangulator
{
    private List<Vector2> m_points = new List<Vector2>();

    public Triangulator (Vector2[] points) {
        m_points = new List<Vector2>(points);
    }

    public int[] Triangulate() {
        List<int> indices = new List<int>();

        int n = m_points.Count;
        if (n < 3)
            return indices.ToArray();

        int[] V = new int[n];
        if (Area() > 0) {
            for (int v = 0; v < n; v++)
                V[v] = v;
        }
        else {
            for (int v = 0; v < n; v++)
                V[v] = (n - 1) - v;
        }

        int nv = n;
        int count = 2 * nv;
        for (int m = 0, v = nv - 1; nv > 2; ) {
            if ((count--) <= 0)
                return indices.ToArray();

            int u = v;
            if (nv <= u)
                u = 0;
            v = u + 1;
            if (nv <= v)
                v = 0;
            int w = v + 1;
            if (nv <= w)
                w = 0;

            if (Snip(u, v, w, nv, V)) {
                int a, b, c, s, t;
                a = V[u];
                b = V[v];
                c = V[w];
                indices.Add(a);
                indices.Add(b);
                indices.Add(c);
                m++;
                for (s = v, t = v + 1; t < nv; s++, t++)
                    V[s] = V[t];
                nv--;
                count = 2 * nv;
            }
        }

        indices.Reverse();
        return indices.ToArray();
    }

    private float Area () {
        int n = m_points.Count;
        float A = 0.0f;
        for (int p = n - 1, q = 0; q < n; p = q++) {
            Vector2 pval = m_points[p];
            Vector2 qval = m_points[q];
            A += pval.x * qval.y - qval.x * pval.y;
        }
        return (A * 0.5f);
    }

    private bool Snip (int u, int v, int w, int n, int[] V) {
        int p;
        Vector2 A = m_points[V[u]];
        Vector2 B = m_points[V[v]];
        Vector2 C = m_points[V[w]];
        if (Mathf.Epsilon > (((B.x - A.x) * (C.y - A.y)) - ((B.y - A.y) * (C.x - A.x))))
            return false;
        for (p = 0; p < n; p++) {
            if ((p == u) || (p == v) || (p == w))
                continue;
            Vector2 P = m_points[V[p]];
            if (InsideTriangle(A, B, C, P))
                return false;
        }
        return true;
    }

    private bool InsideTriangle (Vector2 A, Vector2 B, Vector2 C, Vector2 P) {
        float ax, ay, bx, by, cx, cy, apx, apy, bpx, bpy, cpx, cpy;
        float cCROSSap, bCROSScp, aCROSSbp;

        ax = C.x - B.x; ay = C.y - B.y;
        bx = A.x - C.x; by = A.y - C.y;
        cx = B.x - A.x; cy = B.y - A.y;
        apx = P.x - A.x; apy = P.y - A.y;
        bpx = P.x - B.x; bpy = P.y - B.y;
        cpx = P.x - C.x; cpy = P.y - C.y;

        aCROSSbp = ax * bpy - ay * bpx;
        cCROSSap = cx * apy - cy * apx;
        bCROSScp = bx * cpy - by * cpx;

        return ((aCROSSbp >= 0.0f) && (bCROSScp >= 0.0f) && (cCROSSap >= 0.0f));
    }
}