js通过循环多张图片实现动画效果

以小鱼摇尾巴和眨眼睛为例

动画思路：

1.将图片资源放在数组里面

2.通过计时器来设定间隔时间

3.通过计数器来取相应的图片

第一步：基本框架，鱼身体

<body>
    <canvas id="canvas1" width="800" height="600"></canvas>
</body>

 document.body.onload = game;

 var can1,
     ctx1,
     canWidth,
     canHeight,
     lastTime = Date.now(),
     deltaTime = 0,
     body = new Image();

 function game() {
     init();
     gameloop();
 }

 function init() {
     can1 = document.getElementById("canvas1"); //fonr--fishes, UI, circles, dust
     ctx1 = can1.getContext("2d");
     canWidth = can1.width;
     canHeight = can1.height;

     body.src = './src/baby.png';
 }

 function bodyDraw(){
     ctx1.drawImage( body, -body.width * 0.5, -body.height * 0.5);
 }

 function gameloop() {
     requestAnimFrame(gameloop);

     //时间帧间隔
     var now = Date.now();
     deltaTime = now - lastTime;
     lastTime = now;

     ctx1.clearRect(0, 0, canWidth, canHeight); 

     bodyDraw();
  }

  window.requestAnimFrame = (function() {
     return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame ||
         function( /* function FrameRequestCallback */ callback, /* DOMElement Element */ element) {
             return window.setTimeout(callback, 1000 / 60);
         };
 })();

第二步：摇动尾巴

1.图片资源有8张，从tail0.png ~ tail7.png

2.尾巴是匀速的运动，间隔时间为固定值

 var bTailTimer, //计时器
     bTailCount, //计数器
     babyTail = []; //图片数组

 function init() {
 //尾巴初始化
     bTailTimer = 0;     bTailCount = 0;     for (var i = 0; i < 8; i++) {
         babyTail[i] = new Image();
         babyTail[i].src = './src/tail' + i +'.png';
     }
 }

 function tailDraw(){
     bTailTimer += deltaTime;
     if(bTailTimer > 50){
         bTailCount = (bTailCount + 1)% 8;
         bTailTimer %= 50; //初始化计数器
     }
     ctx1.drawImage( babyTail[bTailCount], -babyTail[bTailCount].width * 0.5, -babyTail[bTailCount].height * 0.5);
 }

 function gameloop() {
  ctx1.clearRect(0, 0, canWidth, canHeight); 

     bodyDraw();
     tailDraw();
  }

第二步：眨眼睛

1.图片资源有2张，从eye0.png ~ eye7.png

2.眼睛睁开时间不定时，闭上时间固定值

 var bEyeTimer,
     bEyeCount,
     bEyeInterval, //时间间隔变量
     babyEye = [];

 function init() {
 //眼睛初始化
     bEyeTimer = 0;
     bEyeCount = 0;
     bEyeInterval = 1000; //间隔时间
     for (var i = 0; i < 2; i++) {
         babyEye[i] = new Image();
         babyEye[i].src = './src/Eye' + i + '.png';
     }
 }

 function eyeDraw() {
     bEyeTimer += deltaTime;
     if (bEyeTimer > bEyeInterval)
     {
         bEyeCount = (bEyeCount + 1)% 2;
         bEyeTimer %= bEyeInterval;

         if (bEyeCount == 0)
         {
             //眼睛睁开保持的时间随机
             bEyeInterval = Math.random() * 1500 + 2000; //[2000,3500)
         } else
         {
             //眼睛闭上保持时间固定为100ms
             bEyeInterval = 100;
         }
     }
 }

 function gameloop() {
 eyeDraw();
  }