sneak/Shared/World.cs

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using System;
using System.Collections.Generic;
using System.Linq;

namespace SemiColinGames {
  class Terrain {

    public static Terrain FromSymbol(char symbol) {
      if (mapping.ContainsKey(symbol)) {
        return mapping[symbol];
      } else {
        return null;
      }
    }

    private static Dictionary<char, Terrain> mapping = new Dictionary<char, Terrain>();

    public static Terrain Grass = new Terrain('=', true);
    public static Terrain GrassL = new Terrain('<', true);
    public static Terrain GrassR = new Terrain('>', true);
    public static Terrain Rock = new Terrain('.', true);
    public static Terrain RockL = new Terrain('[', true);
    public static Terrain RockR = new Terrain(']', true);
    public static Terrain WaterL = new Terrain('~', false);
    public static Terrain WaterR = new Terrain('`', false);
    public static Terrain Block = new Terrain('X', true);
    public static Terrain Spike = new Terrain('^', true);
    public static Terrain Wood = new Terrain('_', true);
    public static Terrain WoodL = new Terrain('(', true);
    public static Terrain WoodR = new Terrain(')', true);
    public static Terrain WoodVert = new Terrain('|', false);
    public static Terrain WoodVertL = new Terrain('/', false);
    public static Terrain WoodVertR = new Terrain('\\', false);
    public static Terrain WoodBottom = new Terrain('v', false);
    public static Terrain FenceL = new Terrain('d', false);
    public static Terrain Fence = new Terrain('f', false);
    public static Terrain FencePost = new Terrain('x', false);
    public static Terrain FenceR = new Terrain('b', false);

    public bool IsObstacle { get; private set; }

    private Terrain(char symbol, bool isObstacle) {
      if (mapping.ContainsKey(symbol)) {
        throw new ArgumentException("already have a terrain with symbol " + symbol);
      }
      IsObstacle = isObstacle;
      mapping[symbol] = this;
    }
  }

  class TileFactory {

    struct TextureSource {
      public Texture2D texture;
      public Rectangle source;

      public TextureSource(Texture2D texture, Rectangle source) {
        this.texture = texture;
        this.source = source;
      }
    }

    readonly Dictionary<Terrain, TextureSource> terrainToTexture;

    public TileFactory() {
      terrainToTexture = new Dictionary<Terrain, TextureSource>() {
        { Terrain.GrassL, GetTextureSource(Textures.Grassland, 2, 0) },
        { Terrain.Grass, GetTextureSource(Textures.Grassland, 3, 0) },
        { Terrain.GrassR, GetTextureSource(Textures.Grassland, 4, 0) },
        { Terrain.Rock, GetTextureSource(Textures.Grassland, 3, 1) },
        { Terrain.RockL, GetTextureSource(Textures.Grassland, 1, 2) },
        { Terrain.RockR, GetTextureSource(Textures.Grassland, 5, 2) },
        { Terrain.WaterL, GetTextureSource(Textures.Grassland, 9, 2) },
        { Terrain.WaterR, GetTextureSource(Textures.Grassland, 10, 2) },
        { Terrain.Block, GetTextureSource(Textures.Ruins, 2, 0) },
        { Terrain.Spike, GetTextureSource(Textures.Grassland, 11, 8) },
        { Terrain.Wood, GetTextureSource(Textures.Grassland, 10, 3) },
        { Terrain.WoodL, GetTextureSource(Textures.Grassland, 9, 3) },
        { Terrain.WoodR, GetTextureSource(Textures.Grassland, 12, 3) },
        { Terrain.WoodVert, GetTextureSource(Textures.Grassland, 9, 5) },
        { Terrain.WoodVertL, GetTextureSource(Textures.Grassland, 9, 4) },
        { Terrain.WoodVertR, GetTextureSource(Textures.Grassland, 12, 4) },
        { Terrain.WoodBottom, GetTextureSource(Textures.Grassland, 10, 5) },
        { Terrain.FenceL, GetTextureSource(Textures.Grassland, 5, 4) },
        { Terrain.Fence, GetTextureSource(Textures.Grassland, 6, 4) },
        { Terrain.FencePost, GetTextureSource(Textures.Grassland, 7, 4) },
        { Terrain.FenceR, GetTextureSource(Textures.Grassland, 8, 4) },
      };
    }

    public Tile MakeTile(Terrain terrain, Rectangle position) {
      TextureSource textureSource = terrainToTexture[terrain];
      return new Tile(terrain, position, textureSource.texture, textureSource.source);
    }

    private TextureSource GetTextureSource(Texture2D texture, int x, int y) {
      int size = World.TileSize;
      Rectangle position = new Rectangle(x * size, y * size, size, size);
      return new TextureSource(texture, position);
    }
  }

  class Tile {
    readonly Texture2D texture;
    readonly Rectangle textureSource;

    public Tile(Terrain terrain, Rectangle position, Texture2D texture, Rectangle textureSource) {
      Terrain = terrain;
      Position = position;
      this.texture = texture;
      this.textureSource = textureSource;
    }

    public Rectangle Position { get; private set; }
    public Terrain Terrain { get; private set; }

    public void Draw(SpriteBatch spriteBatch) {
      spriteBatch.Draw(texture, Position.Location.ToVector2(), textureSource, Color.White);
    }
  }

  class World {

    public const int TileSize = 16;
    readonly Tile[] tiles;
    readonly Tile[] decorations;

    // Size of World in terms of tile grid.
    private readonly int tileWidth;
    private readonly int tileHeight;

    // Size of World in pixels.
    public int Width {
      get { return tileWidth * TileSize; }
    }

    public int Height {
      get { return tileHeight * TileSize; }
    }

    public World(string levelSpecification) {
      TileFactory factory = new TileFactory();
      var tilesList = new List<Tile>();
      var decorationsList = new List<Tile>();
      string[] worldDesc = levelSpecification.Split('\n');
      tileWidth = worldDesc.AsQueryable().Max(a => a.Length);
      tileHeight = worldDesc.Length;
      Debug.WriteLine("world size: {0}x{1}", tileWidth, tileHeight);
      for (int i = 0; i < tileWidth; i++) {
        for (int j = 0; j < tileHeight; j++) {
          if (i < worldDesc[j].Length) {
            char key = worldDesc[j][i];
            Terrain terrain = Terrain.FromSymbol(key);
            if (terrain != null) {
              var position = new Rectangle(i * TileSize, j * TileSize, TileSize, TileSize);
              Tile tile = factory.MakeTile(terrain, position);
              if (tile.Terrain.IsObstacle) {
                tilesList.Add(tile);
              } else {
                decorationsList.Add(tile);
              }
            }
          }
        }
      }
      tiles = tilesList.ToArray();
      decorations = decorationsList.ToArray();

      // Because we added tiles from left to right, the CollisionTargets are sorted by x-position.
      // We maintain this invariant so that it's possible to efficiently find CollisionTargets that
      // are nearby a given x-position.
      CollisionTargets = new AABB[tiles.Length + 2];

      // Add a synthetic collisionTarget on the left side of the world.
      CollisionTargets[0] = new AABB(new Vector2(-1, 0), new Vector2(1, float.MaxValue));

      // Now add all the normal collisionTargets for every static terrain tile.
      Vector2 halfSize = new Vector2(TileSize / 2, TileSize / 2);
      for (int i = 0; i < tiles.Length; i++) {
        Vector2 center = new Vector2(
          tiles[i].Position.Left + halfSize.X, tiles[i].Position.Top + halfSize.Y);
        CollisionTargets[i + 1] = new AABB(center, halfSize);
      }

      // Add a final synthetic collisionTarget on the right side of the world.
      CollisionTargets[tiles.Length + 1] = new AABB(
          new Vector2(Width + 1, 0), new Vector2(1, float.MaxValue));
    }

    public void DrawBackground(SpriteBatch spriteBatch) {
      foreach (Tile t in decorations) {
        t.Draw(spriteBatch);
      }
    }

    public void DrawForeground(SpriteBatch spriteBatch) {
      foreach (Tile t in tiles) {
        t.Draw(spriteBatch);
      }
    }

    public AABB[] CollisionTargets { get; }
  }
}