HTML5 Canvas动画效果演示

时间：2023-12-25 14:37:19

HTML5 Canvas动画效果演示

主要思想：

首先要准备一张有连续帧的图片，然后利用HTML5 Canvas的draw方法在不同的时间

间隔绘制不同的帧，这样看起来就像动画在播放。

关键技术点：

JavaScript 函数setTimeout()有两个参数，第一个是参数可以传递一个JavaScript方法，

另外一个参数代表间隔时间，单位为毫秒数。代码示例：

setTimeout( update, 1000/30);

Canvas的API-drawImage()方法，需要指定全部9个参数：

ctx.drawImage(myImage, offw, offh, width,height, x2, y2, width, height);

其中offw, offh是指源图像的起始坐标点，width, height表示源图像的宽与高，x2,y2表

示源图像在目标Canvas上的起始坐标点。

一个22帧的大雁飞行图片实现的效果：

HTML5 Canvas动画效果演示

源图像：

HTML5 Canvas动画效果演示

程序代码：

<!DOCTYPE html>

<html>

<head>

<meta http-equiv="X-UA-Compatible" content="chrome=IE8">

<meta http-equiv="Content-type" content="text/html;charset=UTF-8">

<title>Canvas Mouse Event Demo</title>

<link href="default.css" rel="stylesheet" />

	<script>

		var ctx = null; // global variable 2d context

		var started = false;

		var mText_canvas = null;

		var x = 0, y =0;

		var frame = 0; // 22 5*5 + 2

		var imageReady = false;

		var myImage = null;

		var px = 300;

		var py = 300;

		var x2 = 300;

		var y2 = 0;

		window.onload = function() {

			var canvas = document.getElementById("animation_canvas");

			console.log(canvas.parentNode.clientWidth);

			canvas.width = canvas.parentNode.clientWidth;

			canvas.height = canvas.parentNode.clientHeight;

			if (!canvas.getContext) {

			    console.log("Canvas not supported. Please install a HTML5 compatible browser.");

			    return;

			}

			// get 2D context of canvas and draw rectangel

			ctx = canvas.getContext("2d");

			ctx.fillStyle="black";

			ctx.fillRect(0, 0, canvas.width, canvas.height);

			myImage = document.createElement('img');

			myImage.src = "../robin.png";

			myImage.onload = loaded();

		}  

		function loaded() {

		    imageReady = true;

		    setTimeout( update, 1000/30);

		}

		function redraw() {

			ctx.clearRect(0, 0, 460, 460)

			ctx.fillStyle="black";

			ctx.fillRect(0, 0, 460, 460);

			// find the index of frames in image

			var height = myImage.naturalHeight/5;

			var width = myImage.naturalWidth/5;

			var row = Math.floor(frame / 5);

			var col = frame - row * 5;

			var offw = col * width;

			var offh = row * height;

			// first robin

			px = px - 5;

			py = py - 5;

			if(px < -50) {

				px = 300;

			}

			if(py < -50) {

				py = 300;

			}

			//var rate = (frame+1) /22;

			//var rw = Math.floor(rate * width);

			//var rh = Math.floor(rate * height);

			ctx.drawImage(myImage, offw, offh, width, height, px, py, width, height);

			// second robin

			x2 = x2 - 5;

			y2 = y2 + 5;

			if(x2 < -50) {

				x2 = 300;

				y2 = 0;

			}

			ctx.drawImage(myImage, offw, offh, width, height, x2, y2, width, height);

		}

		function update() {

		    redraw();

		    frame++;

		    if (frame >= 22) frame = 0;

		    setTimeout( update, 1000/30);

		}

	</script>

</head>

<body>

	<h1>HTML Canvas Animations Demo - By Gloomy Fish</h1>

	<pre>Play Animations</pre>

	<div id="my_painter">

		<canvas id="animation_canvas"></canvas>

	</div>

</body>

</html>

发现上传透明PNG格式有点问题，所以我上传

不透明的图片。可以用其它图片替换，替换以后

请修改最大帧数从22到你的实际帧数即可运行。

相关文章