/Assets/MeshGenerator.cs

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

public class MeshGenerator : MonoBehaviour {

    public SquareGrid squareGrid;
    public MeshFilter walls;
    public MeshFilter cave;

    public bool is2D;

    List<Vector3> vertices;
    List<int> triangles;

    Dictionary<int,List<Triangle>> triangleDictionary = new Dictionary<int, List<Triangle>> ();
    List<List<int>> outlines = new List<List<int>> ();
    HashSet<int> checkedVertices = new HashSet<int>();

    public void GenerateMesh(int[,] map, float squareSize) {

        triangleDictionary.Clear ();
        outlines.Clear ();
        checkedVertices.Clear ();

        squareGrid = new SquareGrid(map, squareSize);

        vertices = new List<Vector3>();
        triangles = new List<int>();

        for (int x = 0; x < squareGrid.squares.GetLength(0); x ++) {
            for (int y = 0; y < squareGrid.squares.GetLength(1); y ++) {
                TriangulateSquare(squareGrid.squares[x,y]);
            }
        }

        Mesh mesh = new Mesh();
        cave.mesh = mesh;

        mesh.vertices = vertices.ToArray();
        mesh.triangles = triangles.ToArray();
        mesh.RecalculateNormals();

        int tileAmount = 10;
        Vector2[] uvs = new Vector2[vertices.Count];
        for (int i =0; i < vertices.Count; i ++) {
            float percentX = Mathf.InverseLerp(-map.GetLength(0)/2*squareSize,map.GetLength(0)/2*squareSize,vertices[i].x) * tileAmount;
            float percentY = Mathf.InverseLerp(-map.GetLength(0)/2*squareSize,map.GetLength(0)/2*squareSize,vertices[i].z) * tileAmount;
            uvs[i] = new Vector2(percentX,percentY);
        }
        mesh.uv = uvs;
    

        if (is2D) {
            Generate2DColliders();
        } else {
            CreateWallMesh ();
        }
    }

    void CreateWallMesh() {

        CalculateMeshOutlines ();

        List<Vector3> wallVertices = new List<Vector3> ();
        List<int> wallTriangles = new List<int> ();
        Mesh wallMesh = new Mesh ();
        float wallHeight = 5;

        foreach (List<int> outline in outlines) {
            for (int i = 0; i < outline.Count -1; i ++) {
                int startIndex = wallVertices.Count;
                wallVertices.Add(vertices[outline[i]]); // left
                wallVertices.Add(vertices[outline[i+1]]); // right
                wallVertices.Add(vertices[outline[i]] - Vector3.up * wallHeight); // bottom left
                wallVertices.Add(vertices[outline[i+1]] - Vector3.up * wallHeight); // bottom right

                wallTriangles.Add(startIndex + 0);
                wallTriangles.Add(startIndex + 2);
                wallTriangles.Add(startIndex + 3);

                wallTriangles.Add(startIndex + 3);
                wallTriangles.Add(startIndex + 1);
                wallTriangles.Add(startIndex + 0);
            }
        }
        wallMesh.vertices = wallVertices.ToArray ();
        wallMesh.triangles = wallTriangles.ToArray ();
        walls.mesh = wallMesh;

        MeshCollider wallCollider = walls.gameObject.AddComponent<MeshCollider> ();
        wallCollider.sharedMesh = wallMesh;
    }

    void Generate2DColliders() {

        EdgeCollider2D[] currentColliders = gameObject.GetComponents<EdgeCollider2D> ();
        for (int i = 0; i < currentColliders.Length; i++) {
            Destroy(currentColliders[i]);
        }

        CalculateMeshOutlines ();

        foreach (List<int> outline in outlines) {
            EdgeCollider2D edgeCollider = gameObject.AddComponent<EdgeCollider2D>();
            Vector2[] edgePoints = new Vector2[outline.Count];

            for (int i =0; i < outline.Count; i ++) {
                edgePoints[i] = new Vector2(vertices[outline[i]].x,vertices[outline[i]].z);
            }
            edgeCollider.points = edgePoints;
        }

    }

    void TriangulateSquare(Square square) {
        switch (square.configuration) {
        case 0:
            break;

        // 1 points:
        case 1:
            MeshFromPoints(square.centreLeft, square.centreBottom, square.bottomLeft);
            break;
        case 2:
            MeshFromPoints(square.bottomRight, square.centreBottom, square.centreRight);
            break;
        case 4:
            MeshFromPoints(square.topRight, square.centreRight, square.centreTop);
            break;
        case 8:
            MeshFromPoints(square.topLeft, square.centreTop, square.centreLeft);
            break;

        // 2 points:
        case 3:
            MeshFromPoints(square.centreRight, square.bottomRight, square.bottomLeft, square.centreLeft);
            break;
        case 6:
            MeshFromPoints(square.centreTop, square.topRight, square.bottomRight, square.centreBottom);
            break;
        case 9:
            MeshFromPoints(square.topLeft, square.centreTop, square.centreBottom, square.bottomLeft);
            break;
        case 12:
            MeshFromPoints(square.topLeft, square.topRight, square.centreRight, square.centreLeft);
            break;
        case 5:
            MeshFromPoints(square.centreTop, square.topRight, square.centreRight, square.centreBottom, square.bottomLeft, square.centreLeft);
            break;
        case 10:
            MeshFromPoints(square.topLeft, square.centreTop, square.centreRight, square.bottomRight, square.centreBottom, square.centreLeft);
            break;

        // 3 point:
        case 7:
            MeshFromPoints(square.centreTop, square.topRight, square.bottomRight, square.bottomLeft, square.centreLeft);
            break;
        case 11:
            MeshFromPoints(square.topLeft, square.centreTop, square.centreRight, square.bottomRight, square.bottomLeft);
            break;
        case 13:
            MeshFromPoints(square.topLeft, square.topRight, square.centreRight, square.centreBottom, square.bottomLeft);
            break;
        case 14:
            MeshFromPoints(square.topLeft, square.topRight, square.bottomRight, square.centreBottom, square.centreLeft);
            break;

        // 4 point:
        case 15:
            MeshFromPoints(square.topLeft, square.topRight, square.bottomRight, square.bottomLeft);
            checkedVertices.Add(square.topLeft.vertexIndex);
            checkedVertices.Add(square.topRight.vertexIndex);
            checkedVertices.Add(square.bottomRight.vertexIndex);
            checkedVertices.Add(square.bottomLeft.vertexIndex);
            break;
        }

    }

    void MeshFromPoints(params Node[] points) {
        AssignVertices(points);

        if (points.Length >= 3)
            CreateTriangle(points[0], points[1], points[2]);
        if (points.Length >= 4)
            CreateTriangle(points[0], points[2], points[3]);
        if (points.Length >= 5) 
            CreateTriangle(points[0], points[3], points[4]);
        if (points.Length >= 6)
            CreateTriangle(points[0], points[4], points[5]);

    }

    void AssignVertices(Node[] points) {
        for (int i = 0; i < points.Length; i ++) {
            if (points[i].vertexIndex == -1) {
                points[i].vertexIndex = vertices.Count;
                vertices.Add(points[i].position);
            }
        }
    }

    void CreateTriangle(Node a, Node b, Node c) {
        triangles.Add(a.vertexIndex);
        triangles.Add(b.vertexIndex);
        triangles.Add(c.vertexIndex);

        Triangle triangle = new Triangle (a.vertexIndex, b.vertexIndex, c.vertexIndex);
        AddTriangleToDictionary (triangle.vertexIndexA, triangle);
        AddTriangleToDictionary (triangle.vertexIndexB, triangle);
        AddTriangleToDictionary (triangle.vertexIndexC, triangle);
    }

    void AddTriangleToDictionary(int vertexIndexKey, Triangle triangle) {
        if (triangleDictionary.ContainsKey (vertexIndexKey)) {
            triangleDictionary [vertexIndexKey].Add (triangle);
        } else {
            List<Triangle> triangleList = new List<Triangle>();
            triangleList.Add(triangle);
            triangleDictionary.Add(vertexIndexKey, triangleList);
        }
    }

    void CalculateMeshOutlines() {

        for (int vertexIndex = 0; vertexIndex < vertices.Count; vertexIndex ++) {
            if (!checkedVertices.Contains(vertexIndex)) {
                int newOutlineVertex = GetConnectedOutlineVertex(vertexIndex);
                if (newOutlineVertex != -1) {
                    checkedVertices.Add(vertexIndex);

                    List<int> newOutline = new List<int>();
                    newOutline.Add(vertexIndex);
                    outlines.Add(newOutline);
                    FollowOutline(newOutlineVertex, outlines.Count-1);
                    outlines[outlines.Count-1].Add(vertexIndex);
                }
            }
        }
    }

    void FollowOutline(int vertexIndex, int outlineIndex) {
        outlines [outlineIndex].Add (vertexIndex);
        checkedVertices.Add (vertexIndex);
        int nextVertexIndex = GetConnectedOutlineVertex (vertexIndex);

        if (nextVertexIndex != -1) {
            FollowOutline(nextVertexIndex, outlineIndex);
        }
    }

    int GetConnectedOutlineVertex(int vertexIndex) {
        List<Triangle> trianglesContainingVertex = triangleDictionary [vertexIndex];

        for (int i = 0; i < trianglesContainingVertex.Count; i ++) {
            Triangle triangle = trianglesContainingVertex[i];

            for (int j = 0; j < 3; j ++) {
                int vertexB = triangle[j];
                if (vertexB != vertexIndex && !checkedVertices.Contains(vertexB)) {
                    if (IsOutlineEdge(vertexIndex, vertexB)) {
                        return vertexB;
                    }
                }
            }
        }

        return -1;
    }

    bool IsOutlineEdge(int vertexA, int vertexB) {
        List<Triangle> trianglesContainingVertexA = triangleDictionary [vertexA];
        int sharedTriangleCount = 0;

        for (int i = 0; i < trianglesContainingVertexA.Count; i ++) {
            if (trianglesContainingVertexA[i].Contains(vertexB)) {
                sharedTriangleCount ++;
                if (sharedTriangleCount > 1) {
                    break;
                }
            }
        }
        return sharedTriangleCount == 1;
    }

    struct Triangle {
        public int vertexIndexA;
        public int vertexIndexB;
        public int vertexIndexC;
        int[] vertices;

        public Triangle (int a, int b, int c) {
            vertexIndexA = a;
            vertexIndexB = b;
            vertexIndexC = c;

            vertices = new int[3];
            vertices[0] = a;
            vertices[1] = b;
            vertices[2] = c;
        }

        public int this[int i] {
            get {
                return vertices[i];
            }
        }


        public bool Contains(int vertexIndex) {
            return vertexIndex == vertexIndexA || vertexIndex == vertexIndexB || vertexIndex == vertexIndexC;
        }
    }

    public class SquareGrid {
        public Square[,] squares;

        public SquareGrid(int[,] map, float squareSize) {
            int nodeCountX = map.GetLength(0);
            int nodeCountY = map.GetLength(1);
            float mapWidth = nodeCountX * squareSize;
            float mapHeight = nodeCountY * squareSize;

            ControlNode[,] controlNodes = new ControlNode[nodeCountX,nodeCountY];

            for (int x = 0; x < nodeCountX; x ++) {
                for (int y = 0; y < nodeCountY; y ++) {
                    Vector3 pos = new Vector3(-mapWidth/2 + x * squareSize + squareSize/2, 0, -mapHeight/2 + y * squareSize + squareSize/2);
                    controlNodes[x,y] = new ControlNode(pos,map[x,y] == 1, squareSize);
                }
            }

            squares = new Square[nodeCountX -1,nodeCountY -1];
            for (int x = 0; x < nodeCountX-1; x ++) {
                for (int y = 0; y < nodeCountY-1; y ++) {
                    squares[x,y] = new Square(controlNodes[x,y+1], controlNodes[x+1,y+1], controlNodes[x+1,y], controlNodes[x,y]);
                }
            }

        }
    }
    
    public class Square {

        public ControlNode topLeft, topRight, bottomRight, bottomLeft;
        public Node centreTop, centreRight, centreBottom, centreLeft;
        public int configuration;

        public Square (ControlNode _topLeft, ControlNode _topRight, ControlNode _bottomRight, ControlNode _bottomLeft) {
            topLeft = _topLeft;
            topRight = _topRight;
            bottomRight = _bottomRight;
            bottomLeft = _bottomLeft;

            centreTop = topLeft.right;
            centreRight = bottomRight.above;
            centreBottom = bottomLeft.right;
            centreLeft = bottomLeft.above;

            if (topLeft.active)
                configuration += 8;
            if (topRight.active)
                configuration += 4;
            if (bottomRight.active)
                configuration += 2;
            if (bottomLeft.active)
                configuration += 1;
        }

    }

    public class Node {
        public Vector3 position;
        public int vertexIndex = -1;

        public Node(Vector3 _pos) {
            position = _pos;
        }
    }

    public class ControlNode : Node {

        public bool active;
        public Node above, right;

        public ControlNode(Vector3 _pos, bool _active, float squareSize) : base(_pos) {
            active = _active;
            above = new Node(position + Vector3.forward * squareSize/2f);
            right = new Node(position + Vector3.right * squareSize/2f);
        }

    }
}