js通过循环多张图片实现动画效果

时间:2021-04-02 人气:2

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; 8  bTailCount = 0; 9  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();
 }

第三步：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();
 }

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