path: root/files/zh-tw/web/api/canvas_api/tutorial/advanced_animations/index.html

---
title: Advanced animations
slug: Web/API/Canvas_API/Tutorial/Advanced_animations
translation_of: Web/API/Canvas_API/Tutorial/Advanced_animations
---
<div>{{CanvasSidebar}} {{PreviousNext("Web/API/Canvas_API/Tutorial/Basic_animations", "Web/API/Canvas_API/Tutorial/Pixel_manipulation_with_canvas")}}</div>

<div class="summary">
<p>在上一章節，我們做了一些<a href="/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_animations">基礎動畫</a>且知道它的移動方式。在這部分我們更仔細的介紹它的動畫效果且並增加一些特效，使它看起來更高級。</p>
</div>

<h2 id="畫一顆球">畫一顆球</h2>

<p>在這次的動畫練習中使用球來練習。照著下面的步驟完成 canvas 設定。</p>

<pre class="brush: html">&lt;canvas id="canvas" width="600" height="300"&gt;&lt;/canvas&gt;
</pre>

<p>照常理，先在canvas上需要先畫一顆球。創造一個 <code>ball</code> object，它包含的屬性和<code>draw()</code>的方法，使canvas可以在上面繪圖。</p>

<pre class="brush: js">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

var ball = {
  x: 100,
  y: 100,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

ball.draw();</pre>

<p>這裡沒什麼特別的，透過{{domxref("CanvasRenderingContext2D.arc()", "arc()")}}的方法，球事實上只是畫下簡單的圓。</p>

<h2 id="添加速度">添加速度</h2>

<p>現在有了一顆球，準備添加基礎的動畫像我們從<a href="/en-US/docs/Web/API/Canvas_API/Tutorial/Basic_animations">上章節學到的課程</a>。再次使用{{domxref("window.requestAnimationFrame()")}}控制動畫。添加移動的向量速度使球移動到向量點。對於每個幀(frame)，我們使用{{domxref("CanvasRenderingContext2D.clearRect", "clear", "", 1)}}來清除canvas舊的移動幀(frame)。</p>

<pre class="brush: js; highlight:[8,9,24,25]">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 2,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function draw() {
  ctx.clearRect(0,0, canvas.width, canvas.height);
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;
  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function(e) {
  raf = window.requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function(e) {
  window.cancelAnimationFrame(raf);
});

ball.draw();
</pre>

<h2 id="邊界">邊界</h2>

<p>沒有任何邊界碰撞下，球很快就會跑出canvas。這時需要確認球的 <code>x</code> and <code>y</code> 是否超出 canvas 尺寸，若超出則將球的向量顛倒。所以，我們添加了確認條件在<code>draw</code>方法:</p>

<pre class="brush: js">if (ball.y + ball.vy &gt; canvas.height || ball.y + ball.vy &lt; 0) {
  ball.vy = -ball.vy;
}
if (ball.x + ball.vx &gt; canvas.width || ball.x + ball.vx &lt; 0) {
  ball.vx = -ball.vx;
}</pre>

<h3 id="第一個示範">第一個示範</h3>

<p>讓我們看看，看似很遠的行徑它如何行徑。移動你的滑鼠在canvas，使動畫開始。 </p>

<div class="hidden">
<pre class="brush: html">&lt;canvas id="canvas" style="border: 1px solid" width="600" height="300"&gt;&lt;/canvas&gt;</pre>

<pre class="brush: js">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 2,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function draw() {
  ctx.clearRect(0,0, canvas.width, canvas.height);
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;

  if (ball.y + ball.vy &gt; canvas.height ||
      ball.y + ball.vy &lt; 0) {
    ball.vy = -ball.vy;
  }
  if (ball.x + ball.vx &gt; canvas.width ||
      ball.x + ball.vx &lt; 0) {
    ball.vx = -ball.vx;
  }

  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function(e) {
  raf = window.requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function(e) {
  window.cancelAnimationFrame(raf);
});

ball.draw();</pre>
</div>

<p>{{EmbedLiveSample("First_demo", "610", "310")}}</p>

<h2 id="加速性能">加速性能</h2>

<p>為了使移動看起來更真實，你可以照著範例改變速度:</p>

<pre class="brush: js">ball.vy *= .99;
ball.vy += .25;</pre>

<p>這個使每個幀(frame)的垂直向量減少，所以球將只會在地板彈跳直到結束。</p>

<div class="hidden">
<h6 id="Second_demo">Second demo</h6>

<pre class="brush: html">&lt;canvas id="canvas" style="border: 1px solid" width="600" height="300"&gt;&lt;/canvas&gt;</pre>

<pre class="brush: js">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 2,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function draw() {
  ctx.clearRect(0,0, canvas.width, canvas.height);
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;
  ball.vy *= .99;
  ball.vy += .25;

  if (ball.y + ball.vy &gt; canvas.height ||
      ball.y + ball.vy &lt; 0) {
    ball.vy = -ball.vy;
  }
  if (ball.x + ball.vx &gt; canvas.width ||
      ball.x + ball.vx &lt; 0) {
    ball.vx = -ball.vx;
  }

  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function(e) {
  raf = window.requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function(e) {
  window.cancelAnimationFrame(raf);
});

ball.draw();</pre>
</div>

<p>{{EmbedLiveSample("Second_demo", "610", "310")}}</p>

<h2 id="追蹤效果">追蹤效果</h2>

<p>直到現在我們已經使用{{domxref("CanvasRenderingContext2D.clearRect", "clearRect")}}方法清除之前的幀(frames)。如果使用重置半透明{{domxref("CanvasRenderingContext2D.fillRect", "fillRect")}}這個方法，可以更淺顯的看出創造追蹤效果。</p>

<pre class="brush: js">ctx.fillStyle = 'rgba(255, 255, 255, 0.3)';
ctx.fillRect(0, 0, canvas.width, canvas.height);</pre>

<div class="hidden">
<h6 id="Third_demo">Third demo</h6>

<pre class="brush: html">&lt;canvas id="canvas" style="border: 1px solid" width="600" height="300"&gt;&lt;/canvas&gt;</pre>

<pre class="brush: js">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 2,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function draw() {
  ctx.fillStyle = 'rgba(255, 255, 255, 0.3)';
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;
  ball.vy *= .99;
  ball.vy += .25;

  if (ball.y + ball.vy &gt; canvas.height ||
      ball.y + ball.vy &lt; 0) {
    ball.vy = -ball.vy;
  }
  if (ball.x + ball.vx &gt; canvas.width ||
      ball.x + ball.vx &lt; 0) {
    ball.vx = -ball.vx;
  }

  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function(e) {
  raf = window.requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function(e) {
  window.cancelAnimationFrame(raf);
});

ball.draw();</pre>
</div>

<p>{{EmbedLiveSample("Third_demo", "610", "310")}}</p>

<h2 id="增加滑鼠控制">增加滑鼠控制</h2>

<p>為了能控制球使它跟著滑鼠移動，在這個範例使用<code><a href="/en-US/docs/Web/Reference/Events/mousemove">mousemove</a></code> 效果。當 <code><a href="/en-US/docs/Web/Events/click">click</a></code> 事件觸發了這顆球，它又會開始彈跳。</p>

<div class="hidden">
<pre class="brush: html">&lt;canvas id="canvas" style="border: 1px solid" width="600" height="300"&gt;&lt;/canvas&gt;</pre>
</div>

<pre class="brush: js">var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;
var running = false;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 1,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function clear() {
  ctx.fillStyle = 'rgba(255, 255, 255, 0.3)';
  ctx.fillRect(0,0,canvas.width,canvas.height);
}

function draw() {
  clear();
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;

  if (ball.y + ball.vy &gt; canvas.height || ball.y + ball.vy &lt; 0) {
    ball.vy = -ball.vy;
  }
  if (ball.x + ball.vx &gt; canvas.width || ball.x + ball.vx &lt; 0) {
    ball.vx = -ball.vx;
  }

  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mousemove', function(e) {
  if (!running) {
    clear();
    ball.x = e.clientX;
    ball.y = e.clientY;
    ball.draw();
  }
});

canvas.addEventListener('click', function(e) {
  if (!running) {
    raf = window.requestAnimationFrame(draw);
    running = true;
  }
});

canvas.addEventListener('mouseout', function(e) {
  window.cancelAnimationFrame(raf);
  running = false;
});

ball.draw();
</pre>

<p>用你的滑鼠移動這顆球且點擊鬆放它。</p>

<p>{{EmbedLiveSample("Adding_mouse_control", "610", "310")}}</p>

<h2 id="突破性(遊戲)">突破性(遊戲)</h2>

<p>這個小章節只有解釋一些創造高級動畫的技巧。這裡還有更多!如何增加槳,磚塊,到這個 到 <a href="http://en.wikipedia.org/wiki/Breakout_%28video_game%29">Breakout</a> game demo去看，有我們更<a href="/en-US/docs/Games">多遊戲研發</a>的文章! </p>

<h2 id="延伸閱讀">延伸閱讀</h2>

<ul>
 <li>{{domxref("window.requestAnimationFrame()")}}</li>
 <li><a href="/en-US/docs/Games/Techniques/Efficient_animation_for_web_games">Efficient animation for web games</a></li>
</ul>

<p>{{PreviousNext("Web/API/Canvas_API/Tutorial/Basic_animations", "Web/API/Canvas_API/Tutorial/Pixel_manipulation_with_canvas")}}</p>