碰撞檢測(cè)在幾乎任何游戲都是很關(guān)鍵的一個(gè)部分，而碰撞檢測(cè)又決定了游戲的流暢性，它對(duì)流暢性的影響如何之大的原因，在于碰撞檢測(cè)算法越是精確到位，游戲?qū)?huì)運(yùn)行得越緩慢。在碰撞檢測(cè)方面，很明顯需要在準(zhǔn)確性和性能之間進(jìn)行權(quán)衡。
實(shí)現(xiàn)碰撞檢測(cè)最簡(jiǎn)單和快速的方式是通過包圍盒算法。當(dāng)用一個(gè)包圍盒算法時(shí)，就需要在屏幕上的每個(gè)物體（紋理圖像）周圍“畫“一個(gè)盒子（矩形塊），然后檢查這些盒子是否相交，如果產(chǎn)生相交（怎么聽起來這么耳熟？），就即可判斷出是產(chǎn)生碰撞了。經(jīng)典的碰撞游戲可以看看如今某I設(shè)備上風(fēng)靡全球的小鳥
通過物理算法和碰撞檢測(cè)等實(shí)現(xiàn)這只小鳥欺負(fù)小豬的傳說，這點(diǎn)是很值得借鑒滴。
本篇學(xué)習(xí)文章將會(huì)有兩個(gè)紋理圖，一個(gè)圖片做為碰撞塊例如上圖的小鳥，另一個(gè)圖片做為需要在某一地方去檢測(cè)是否與之產(chǎn)生碰撞的紋理，例如上圖的小豬或者城墻。這兩張圖片分別是這樣的：
我是用來檢測(cè)是否有人撞到我的。。。。。
我沒事喜歡撞人。。。。。。
好了。素材己經(jīng)有了，下面就到了如何為這兩個(gè)紋理圖像添加各種出場(chǎng)的告白動(dòng)作了。首先，還是國(guó)際慣例一把，先給出效果圖：
看上圖效果，天上掉下了好多尖尖的小塊呀，快逃命呀，不過小人跑不夠快，被一個(gè)尖尖的小塊砸到了，頓時(shí)滿臉是血，屏幕都被染紅了。悲催咯。。。。
要實(shí)現(xiàn)這個(gè)功能首先我們需要得到小人的碰撞點(diǎn)，和每一個(gè)三角形的碰撞點(diǎn)。以獲得小人碰撞點(diǎn)為例，需要得到小人所在的x 坐標(biāo)和y坐標(biāo)，并且得到小人的寬度和高度。當(dāng)我們獲取到這個(gè)數(shù)據(jù)的時(shí)候，就可以為小人添加一個(gè)包圍圈也叫矩形檢測(cè)塊：
// 獲得小人的磁撞大小和碰撞的地點(diǎn)
//公式為：得到小人所在的x、y 地點(diǎn)，然后在那個(gè)x、y點(diǎn)的區(qū)域高寬
Rectangle personRectangle =
new Rectangle((int)personPosition.X, (int)personPosition.Y,
personTexture.Width, personTexture.Height);
當(dāng)?shù)玫竭@個(gè)矩形塊時(shí)。再依次獲取得到每個(gè)三角形的矩形和其位置使用矩形自帶的函數(shù)Intersects 來檢測(cè)兩個(gè)矩形之者是否產(chǎn)生交接：
// 與上面獲得小人的碰撞點(diǎn)類似
Rectangle blockRectangle =
new Rectangle((int)blockPositions[i].X, (int)blockPositions[i].Y,
blockTexture.Width, blockTexture.Height);
// 如果小人與其中某一個(gè)碰撞紋理的碰撞點(diǎn)產(chǎn)生碰撞
if (personRectangle.Intersects(blockRectangle))
personHit = true; //這時(shí)的碰撞檢測(cè)將生效
如上，如果產(chǎn)生交接即在調(diào)用Draw 的時(shí)候改變屏幕的顏色，即可產(chǎn)生碰撞時(shí)的效果，DEMO源碼為：
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
Texture2D personTexture; //小人紋理圖像
Texture2D blockTexture; //撞擊點(diǎn)紋理圖像
// Person
Vector2 personPosition; //小人2D坐標(biāo)
const int PersonMoveSpeed = 5; //小人移動(dòng)速度
// Blocks
List<Vector2> blockPositions = new List<Vector2>(); //撞擊點(diǎn)集合
float BlockSpawnProbability = 0.1f; //控制撞擊點(diǎn)的下降個(gè)數(shù)
const int BlockFallSpeed = 10; //撞擊點(diǎn)下降速度
Random random = new Random();
bool personHit = false; //是否產(chǎn)生碰撞
Rectangle safeBounds;
const float SafeAreaPortion = 0.05f;
Viewport viewport; //獲得當(dāng)前窗口的寬高對(duì)象
public Game1()
{
graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
// Frame rate is 30 fps by default for Windows Phone.
TargetElapsedTime = TimeSpan.FromTicks(333333);
}
/// <summary>
/// Allows the game to perform any initialization it needs to before starting to run.
/// This is where it can query for any required services and load any non-graphic
/// related content. Calling base.Initialize will enumerate through any components
/// and initialize them as well.
/// </summary>
protected override void Initialize()
{
// TODO: Add your initialization logic here
viewport = graphics.GraphicsDevice.Viewport;
safeBounds = new Rectangle(
(int)(viewport.Width * SafeAreaPortion), //40
(int)(viewport.Height * SafeAreaPortion), //24
(int)(viewport.Width * (1 - 2 * SafeAreaPortion)), //720
(int)(viewport.Height * (1 - 2 * SafeAreaPortion))); //432
// Start the player in the center along the bottom of the screen
base.Initialize();
}
/// <summary>
/// LoadContent will be called once per game and is the place to load
/// all of your content.
/// </summary>
protected override void LoadContent()
{
spriteBatch = new SpriteBatch(GraphicsDevice);
blockTexture = Content.Load<Texture2D>("Block");
personTexture = Content.Load<Texture2D>("Person");
personPosition.X = (safeBounds.Width - personTexture.Width) / 2; //小人的坐標(biāo)縱向在屏幕居中
personPosition.Y = safeBounds.Height - personTexture.Height; //小人的坐標(biāo)豎向在屏幕底下居中
// TODO: use this.Content to load your game content here
}
/// <summary>
/// UnloadContent will be called once per game and is the place to unload
/// all content.
/// </summary>
protected override void UnloadContent()
{
// TODO: Unload any non ContentManager content here
}
/// <summary>
/// Allows the game to run logic such as updating the world,
/// checking for collisions, gathering input, and playing audio.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Update(GameTime gameTime)
{
// Allows the game to exit
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
this.Exit();
TouchCollection touch = TouchPanel.GetState();
if (touch.Count>0)
{
if (touch[0].Position.X > viewport.Width / 2)
{
personPosition.X += PersonMoveSpeed;
}
else
{
personPosition.X -= PersonMoveSpeed;
}
}
double ran = random.NextDouble();
// TODO: Add your update logic here
if (ran < BlockSpawnProbability) //隨機(jī)循環(huán)Double 型如果隨機(jī)的double 小于0.01f這樣做是避免產(chǎn)生的撞擊 點(diǎn)太多
{
float x = (float)random.NextDouble() *//在屏幕隨機(jī)出現(xiàn)
(graphics.GraphicsDevice.Viewport.Width - blockTexture.Width);//為了不超出屏幕
Vector2 v = new Vector2(x, 1);
blockPositions.Add(v);
}
// 獲得小人的磁撞大小和碰撞的地點(diǎn)
//公式為：得到小人所在的x、y 地點(diǎn)，然后在那個(gè)x、y點(diǎn)的區(qū)域高寬
Rectangle personRectangle =
new Rectangle((int)personPosition.X, (int)personPosition.Y,
personTexture.Width, personTexture.Height);
// Update each block
personHit = false; //默認(rèn)為不碰撞狀態(tài)
for (int i = 0; i < blockPositions.Count; i++) //循環(huán)所有在集合里面的碰撞紋理
{
// 使里面的所有元素全部下降
blockPositions[i] =
new Vector2(blockPositions[i].X, //X坐標(biāo)不變
blockPositions[i].Y + BlockFallSpeed); //豎坐標(biāo)為當(dāng)前的Y座標(biāo)每次加上下降的速度常量
// 與上面獲得小人的碰撞點(diǎn)類似
Rectangle blockRectangle =
new Rectangle((int)blockPositions[i].X, (int)blockPositions[i].Y,
blockTexture.Width, blockTexture.Height);
// 如果小人與其中某一個(gè)碰撞紋理的碰撞點(diǎn)產(chǎn)生碰撞
if (personRectangle.Intersects(blockRectangle))
personHit = true; //這時(shí)的碰撞檢測(cè)將生效
// 如果有碰撞紋理超屏幕
if (blockPositions[i].Y > graphics.GraphicsDevice.Viewport.Height)
{
//從集合里面移出該碰撞點(diǎn)
blockPositions.RemoveAt(i);
//當(dāng)刪除了其中一個(gè)碰撞點(diǎn)時(shí)，下一個(gè)碰撞點(diǎn)的索引將跟當(dāng)前移除的碰撞點(diǎn)是一樣的，所以循環(huán)變量自動(dòng)減1
i--;
}
}
base.Update(gameTime);
}
/// <summary>
/// This is called when the game should draw itself.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
GraphicsDevice device = graphics.GraphicsDevice;
// TODO: Add your drawing code here
if (personHit) //當(dāng)產(chǎn)生碰撞
{
device.Clear(Color.Red);
}
else
{
device.Clear(Color.CornflowerBlue);
}
spriteBatch.Begin();
// Draw person
spriteBatch.Draw(personTexture, personPosition, Color.White);
// Draw blocks
foreach (Vector2 blockPosition in blockPositions)
spriteBatch.Draw(blockTexture, blockPosition, Color.White);
spriteBatch.End();
base.Draw(gameTime);
}
}
輕輕松松的調(diào)用幾個(gè)現(xiàn)成的方法和利用刷新機(jī)制就可以實(shí)現(xiàn)這個(gè)碰撞檢測(cè)功能。當(dāng)然碰撞檢測(cè)還不止這么簡(jiǎn)單，還可以更詳細(xì)的使用逐點(diǎn)檢測(cè)的方法檢測(cè)碰撞。
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