XNA之RPG游戏开发教程之五

上一节我们说到游戏中的地图绘制，我们在TileMap类中为GameplayScreen绘制地图，但要模拟真实的游戏地图，需要做到地图的滚动，以前我们经常会用现成的图片，利用图片的滚动模拟背景移动。现在要实现游戏地图的个性化，要用Tile绘制地图,就需要一个2D的Camera类，站在player的Position上会有一个视野范围，就在这个视野范围内绘制地图，用这种方法来实现动态地图的模拟。接下来建立一个Camera类如下

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
namespace XRpgLibrary.TileEngine
{
public class Camera
 {
 #region Field Region
Vector2 position;//Camera位置
float speed;//Camera的移动速度
float zoom;//Camera的放大缩小倍数
Rectangle viewportRectangle;
 #endregion
 #region Property Region
public Vector2 Position
 {
get { return position; }
private set { position = value; }
 }
public float Speed
 {
get { return speed; }
set
 {
 speed = (float)MathHelper.Clamp(speed, 1f, 16f);//该函数的作用是将speed值限定在1和16之间，大于16，返回16，小于1，返回1，在两者之间返回true
 }
 }
public float Zoom
 {get { return zoom; }
 }
 #endregion
 #region Constructor Region
public Camera(Rectangle viewportRect)//用视野矩阵来初始化相机
 {
 speed = 4f;
 zoom = 1f;
 viewportRectangle = viewportRect;
 }
public Camera(Rectangle viewportRect, Vector2 position)
 {
 speed = 4f;
 zoom = 1f;
 viewportRectangle = viewportRect;
 Position = position;
 }
 #endregion
 #region Method Region//根据键盘控制移动，实际上将Camera与Player联系在一起
public void Update(GameTime gameTime)
 {
if (InputHandler.KeyDown(Keys.Left))
 position.X -= speed;
else if (InputHandler.KeyDown(Keys.Right))
 position.X += speed;
if (InputHandler.KeyDown(Keys.Up))
 position.Y -= speed;
else if (InputHandler.KeyDown(Keys.Down))
 position.Y += speed;
 }
 #endregion
 }
}

接下来就是为游戏中添加玩家player类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using XRpgLibrary;
using XRpgLibrary.TileEngine;
namespace EyesOfTheDragon.Components
{
public class Player
 {
 #region Field Region
Camera camera;//Camera对象，将其与玩家联系起来
Game1 gameRef;//Game对象，将其与玩家联系起来
 #endregion
 #region Property Region
public Camera Camera
 {
get { return camera; }
set { camera = value; }
 }
 #endregion
 #region Constructor Region在构建玩家的同时构建Camera
public Player(Game game)
 { 
 gameRef = (Game1)game;
 camera = new Camera(gameRef.ScreenRectangle);
 }
 #endregion
 #region Method Region
public void Update(GameTime gameTime)
 {
 camera.Update(gameTime);
 }
public void Draw(GameTime gameTime, SpriteBatch spriteBatch)
 {
 }
 #endregion
 }
}

接着就是将Player对象添加到GamePlayScreen中去，这样就会为游戏页面实例化一个玩家对象，同时实例化一个Camera对象来实现地图的滚动

using EyesOfTheDragon.Components;//添加空间引用
#region Field Region
Engine engine = new Engine(32, 32);
Tileset tileset; 
TileMap map;
Player player;//定义对象
#endregion
#region Constructor Region
public GamePlayScreen(Game game, GameStateManager manager)
 : base(game, manager)
{
 player = new Player(game);//构造函数中实例化对象
}
#endregion

在游戏页面的更新中也要更新玩家

public override void Update(GameTime gameTime)
{
 player.Update(gameTime);
 base.Update(gameTime);
}

接下来要更改的就是TileMap类，上节说过，该类是地图绘制的核心类，地图的绘制在Draw方法中实现，上节中是通过不断更改矩形变量destination的X,Y坐标来绘制每个tile，现在要用Camera来更新地图，所以要将Camera作为参数传入Draw方法中，由其来决定绘制tile的X,Y坐标，更新如下

public void Draw(SpriteBatch spriteBatch, Camera camera)
{
Rectangle destination = new Rectangle(0, 0, Engine.TileWidth, Engine.TileHeight);
Tile tile;
foreach (MapLayer layer in mapLayers)
 {
for (int y = 0; y < layer.Height; y++)
 {
  destination.Y = y * Engine.TileHeight - (int)camera.Position.Y;//获得绘制tile的Y坐标
for (int x = 0; x < layer.Width; x++)
 {
 tile = layer.GetTile(x, y);
if (tile.TileIndex == -1 || tile.Tileset == -1)
continue;
 destination.X = x * Engine.TileWidth - (int)camera.Position.X;//获得绘制tile的X坐标
 spriteBatch.Draw(
 tilesets[tile.Tileset].Texture,
 destination,
 tilesets[tile.Tileset].SourceRectangles[tile.TileIndex],
Color.White);
 }
 }
 }
}

这里关于游戏中摄像机的原理，自己解释不太清楚，可以从http://blog.csdn.net/beyondma/article/details/6766914这里获得相关的理论知识

到这里我们运行程序，移动Camera绘制地图，会发现有绘出地图的现象，即Camera移出了窗体边界。这就需要根据地图的大小来控制Camera的移动区域，需要在TileMap类中添加地图宽度，高度的对外属性，在Camera类中根据这些属性来控制Camera的移动区域，地图的左边和上边最好控制，只要保证Camera的Position的X,Y坐标都是非负就能保证其没有越过左边界和上边界，至于下边界和右边界就用地图的宽度和高度来控制

TileMap类中的更新代码如下

#region Field Region
List<Tileset> tilesets;
List<MapLayer> mapLayers;
static int mapWidth;//地图的宽度(tile的个数)
static int mapHeight;//地图的高度
#endregion
#region Property Region
public static int WidthInPixels返回地图宽度方向的像素值
{
  get { return mapWidth * Engine.TileWidth; }
}
public static int HeightInPixels
{
  get { return mapHeight * Engine.TileHeight; }
}
#endregion
#region Constructor Region
public TileMap(List<Tileset> tilesets, List<MapLayer> layers)
{
 this.tilesets = tilesets;
 this.mapLayers = layers;
 mapWidth = mapLayers[0].Width;//以游戏最底层的MapLayer的高度，宽度来初始化
 mapHeight = mapLayers[0].Height;
for (int i = 1; i < layers.Count; i++)
 {
  //检测到各个层之间的宽度，高度不一致，抛出异常
  if (mapWidth != mapLayers[i].Width || mapHeight != mapLayers[i].Height)
     throw new Exception("Map layer size exception");
 }
}
public TileMap(Tileset tileset, MapLayer layer)
{
 tilesets = new List<Tileset>();
 tilesets.Add(tileset);
 mapLayers = new List<MapLayer>(); 
 mapLayers.Add(layer);
 mapWidth = mapLayers[0].Width;//初始化
 mapHeight = mapLayers[0].Height;
}
#endregion

Camera类中的更新如下

public void Update(GameTime gameTime)
{
Vector2 motion = Vector2.Zero;//定义一个向量对象，用来确定Camera的移动方向
if (InputHandler.KeyDown(Keys.Left))
 motion.X = -speed;
else if (InputHandler.KeyDown(Keys.Right))
 motion.X = speed;
if (InputHandler.KeyDown(Keys.Up))
 motion.Y = -speed;
else if (InputHandler.KeyDown(Keys.Down))
 motion.Y = speed;
if (motion != Vector2.Zero)
 motion.Normalize();//对向量进行标准化，然后再乘以Speed才能真的模拟玩家的移动
 position += motion * speed;
 LockCamera();//对Camera的位置进行设定
}

private void LockCamera()
{
 position.X = MathHelper.Clamp(position.X,
 0,
TileMap.WidthInPixels - viewportRectangle.Width);//将Camera的X坐标限定在0和（地图宽度-Camera视野宽度）之间，特别注意要减去Camera视野宽度，这样就不会出现移出游戏窗体的现象
 position.Y = MathHelper.Clamp(position.Y,
 0,
TileMap.HeightInPixels - viewportRectangle.Height);
}
#endregion

最后我们要实现多层地图的绘制，首先要在TileMap类中添加一个AddLayer方法来添加一层地图

public void AddLayer(MapLayer layer)
{
//首先判断每层的宽度，高度是否相同
if (layer.Width != mapWidth && layer.Height != mapHeight)
throw new Exception("Map layer size exception");
 mapLayers.Add(layer);
}

接着就是在GamePlayScreen类中添加这一层地图

protected override void LoadContent()
{ 
 Texture2D tilesetTexture = Game.Content.Load<Texture2D>(@"Tilesets\tileset1");
 tileset = new Tileset(tilesetTexture, 8, 8, 32, 32);
 MapLayer layer = new MapLayer(40, 40);
for (int y = 0; y < layer.Height; y++)
 {
for (int x = 0; x < layer.Width; x++)
 {
  Tile tile = new Tile(0, 0);
  layer.SetTile(x, y, tile);
 }
 }
 map = new TileMap(tileset, layer);
 MapLayer splatter = new MapLayer(40, 40);
 Random random = new Random();
//在40*40的图层上添加80个tile对象
for (int i = 0; i < 80; i++)
 {
  int x = random.Next(0, 40);
  int y = random.Next(0, 40);
  //在2到14这些图片中随机选择一个
  int index = random.Next(2, 14);
  Tile tile = new Tile(index, 0);//利用tile索引来初始化tile对象
  splatter.SetTile(x, y, tile);//往新的图层上添加tile对象
 }
 map.AddLayer(splatter);
base.LoadContent();
}

接着我们想在游戏中添加一些除了草地，植物以为的城市tile，这就需要在GameplayScreen类中新添加一个tileset对象，将从 http://xnagpa.net/xna4/downloads/tilesets2.zip获得的tilesets2.png添加到Content中，更新GamePlayScreen的LoadContent()方法如下

protected override void LoadContent()
{
base.LoadContent();
  Texture2D tilesetTexture = Game.Content.Load<Texture2D>(@"Tilesets\tileset1");
 Tileset tileset1 = new Tileset(tilesetTexture, 8, 8, 32, 32);
 tilesetTexture = Game.Content.Load<Texture2D>(@"Tilesets\tileset2");
 Tileset tileset2 = new Tileset(tilesetTexture, 8, 8, 32, 32);//新建立的tileset对象
 List<Tileset> tilesets = new List<Tileset>();
 tilesets.Add(tileset1);
 tilesets.Add(tileset2);
MapLayer layer = new MapLayer(40, 40);
for (int y = 0; y < layer.Height; y++)
 {
for (int x = 0; x < layer.Width; x++)
 {
 Tile tile = new Tile(0, 0);
 layer.SetTile(x, y, tile);
 }
 }
 MapLayer splatter = new MapLayer(40, 40);
 Random random = new Random();
for (int i = 0; i < 80; i++)
 {
 int x = random.Next(0, 40);
 int y = random.Next(0, 40);
 int index = random.Next(2, 14);
 Tile tile = new Tile(index, 0);//这里的0代表的是第一个tileset集合
 splatter.SetTile(x, y, tile);
 }
//在第二个tileset集合中选择对象设定固定位置的tile
 splatter.SetTile(1, 0, new Tile(0, 1));
 splatter.SetTile(2, 0, new Tile(2, 1));
 splatter.SetTile(3, 0, new Tile(0, 1));
 List<MapLayer> mapLayers = new List<MapLayer>();
 mapLayers.Add(layer);
 mapLayers.Add(splatter);
 map = new TileMap(tilesets, mapLayers);
}

public override void Draw(GameTime gameTime)
{
 GameRef.SpriteBatch.Begin(
 SpriteSortMode.Immediate,
 BlendState.AlphaBlend,
 SamplerState.PointClamp,
 null,
 null,
 null,
 Matrix.Identity);
 map.Draw(GameRef.SpriteBatch, player.Camera);//绘制地图
base.Draw(gameTime);
 GameRef.SpriteBatch.End();
}

OK,今天主要是实现了利用摄像机原理来更新地图，同时实现了多层地图。