sneak/Shared/World.cs

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

namespace SemiColinGames {
  enum Terrain {
    Grass,
    GrassL,
    GrassR,
    Rock,
    RockL,
    RockR,
    Water,
    Block
  }

  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.Water, GetTextureSource(Textures.Grassland, 9, 2) },
        { Terrain.Block, GetTextureSource(Textures.Grassland, 6, 3) },
      };
    }

    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;

    // 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; }
    }

    private static readonly Dictionary<char, Terrain> charToTerrain =
        new Dictionary<char, Terrain>() {
      { '=', Terrain.Grass },
      { '<', Terrain.GrassL },
      { '>', Terrain.GrassR },
      { '.', Terrain.Rock },
      { '[', Terrain.RockL },
      { ']', Terrain.RockR },
      { '~', Terrain.Water },
      { 'X', Terrain.Block }
    };

    public World(string levelSpecification) {
      TileFactory factory = new TileFactory();
      var tilesList = 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];
            if (charToTerrain.ContainsKey(key)) {
              Terrain terrain = charToTerrain[key];
              var position = new Rectangle(i * TileSize, j * TileSize, TileSize, TileSize);
              tilesList.Add(factory.MakeTile(terrain, position));
            }
          }
        }
      }
      tiles = tilesList.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 Draw(SpriteBatch spriteBatch) {
      foreach (Tile t in tiles) {
        t.Draw(spriteBatch);
      }
    }

    public AABB[] CollisionTargets { get; }
  }
}