city-generation/Game/Assets/Scripts/Unity/BuildingMeshGenerator.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using TransportGame.Model;
using UnityEngine;

namespace TransportGame.Unity
{
    public class BuildingMeshGenerator
    {
        public Material BuildingMaterial { get; set; }
        public Texture2D[] Textures { get; set; }

        private GameObject parent = new GameObject("buildings");
        private Map map;
        private System.Random random = new System.Random();

        public IEnumerable Generate(Map map)
        {
            this.map = map;
            int i = 0;

            foreach (var building in map.Buildings)
            {
                GenerateBuilding(building);
                
                if (++i % 10 == 0)
                    yield return null;
            }
        }

        private void GenerateBuilding(Building building)
        {
            List<Vector3> vertices = new List<Vector3>();
            List<UnityEngine.Vector2> uv = new List<UnityEngine.Vector2>();
            List<int> triangles = new List<int>();
            int vIndex = 0;

            if (building.Polygons.Length == 0)
                return;

            float terrainHeight = building.Polygons[0].SelectMany(poly => poly.Points).Min(pt => map.GetHeight((int)pt.X, (int)pt.Y));
            float minY, maxY = terrainHeight;

            for (int i = 0; i < building.Polygons.Length; i++)
            {
                // Update minY and maxY
                minY = maxY;
                maxY += building.LevelHeights[i];

                for (int p = 0; p < building.Polygons[i].Length; p++)
                {
                    // Build mesh
                    var center = building.Polygons[i][p].Position;
                    var pts = building.Polygons[i][p].Points;

                    for (int j = 0; j < pts.Length; j++)
                    {
                        int k = (j + 1) % pts.Length;

                        // Side
                        vertices.Add(new Vector3(pts[j].Y, minY, pts[j].X));
                        vertices.Add(new Vector3(pts[k].Y, minY, pts[k].X));
                        vertices.Add(new Vector3(pts[k].Y, maxY, pts[k].X));
                        vertices.Add(new Vector3(pts[j].Y, maxY, pts[j].X));
                        uv.Add(new UnityEngine.Vector2(pts[j].Y + pts[j].X, minY));
                        uv.Add(new UnityEngine.Vector2(pts[k].Y + pts[k].X, minY));
                        uv.Add(new UnityEngine.Vector2(pts[k].Y + pts[k].X, maxY));
                        uv.Add(new UnityEngine.Vector2(pts[j].Y + pts[j].X, maxY));
                        triangles.AddRange(new[] { vIndex, vIndex + 1, vIndex + 2 });
                        triangles.AddRange(new[] { vIndex, vIndex + 2, vIndex + 3 });
                        vIndex = vertices.Count;

                        // Top side
                        vertices.Add(new Vector3(pts[k].Y, maxY, pts[k].X));
                        vertices.Add(new Vector3(pts[j].Y, maxY, pts[j].X));
                        vertices.Add(new Vector3(center.Y, maxY, center.X));
                        uv.Add(new UnityEngine.Vector2(0, 0));
                        uv.Add(new UnityEngine.Vector2(0, 0));
                        uv.Add(new UnityEngine.Vector2(0, 0));
                        triangles.AddRange(new[] { vIndex + 2, vIndex + 1, vIndex + 0 });
                        vIndex = vertices.Count;
                    }
                }
            }

            // Construct mesh
            Mesh mesh = new Mesh();
            mesh.vertices = vertices.ToArray();
            mesh.triangles = triangles.ToArray();
            mesh.uv = uv.ToArray();
            mesh.RecalculateNormals();

            // Construct game object
            GameObject inters = new GameObject("building");
            inters.transform.parent = parent.transform;

            MeshFilter meshFilter = inters.AddComponent<MeshFilter>();
            meshFilter.mesh = mesh;

            MeshRenderer meshRenderer = inters.AddComponent<MeshRenderer>();
            meshRenderer.materials = new[] { BuildingMaterial };

            // Pick random texture
            if (Textures != null)
            {
                int t = random.Next(Textures.Length);
                meshRenderer.material.mainTexture = Textures[t];
            }
        }
    }
}