HTML5中的Canvas绘图操作（五）

来源：互联网发布：软件测试发展趋势编辑：程序博客网时间：2024/05/16 08:33

好吧这个系列终于要完了，继续展示特效效果。

幻灯片效果：

这个很简单，无非是建立一个定时器去刷新图片。

<!DOCTYPE HTML><html><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Canvas Image Rotator Example</title><script type="text/javascript">var imagePaths = ["images/j0149014.jpg", "images/j0149024.jpg", "images/j0149029.jpg", "images/j0178677.jpg"];var showCanvas = null;var showCanvasCtx = null;var img = document.createElement("img");var currentImage = 0;window.onload = function () {showCanvas = document.getElementById('showCanvas');showCanvasCtx = showCanvas.getContext('2d');img.setAttribute('width','600');img.setAttribute('height','400');switchImage();// start the animationsetInterval(switchImage,3000);}function switchImage() {img.setAttribute('src',imagePaths[currentImage++]);img.onload = function() {if (currentImage >= imagePaths.length)currentImage = 0;showCanvasCtx.drawImage(img,0,0,600,400);}}</script></head><body><canvas id='showCanvas' width='600' height='400'>Canvas Not Supported</canvas></body></html>

对于幻灯片效果做一下平滑处理，主要用到了globalAlpha：

<!DOCTYPE HTML><html><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Canvas Image Rotator Example</title><script type="text/javascript">var imagePaths = ["images/j0149014.jpg", "images/j0149024.jpg", "images/j0149029.jpg", "images/j0178677.jpg"];var showCanvas = null;var showCanvasCtx = null;var img = document.createElement("img");var currentImage = 0;var revealTimer;window.onload = function () {showCanvas = document.getElementById('showCanvas');showCanvasCtx = showCanvas.getContext('2d');img.setAttribute('width','600');img.setAttribute('height','400');switchImage();// start the animationsetInterval(switchImage,3000);}function switchImage() {img.setAttribute('src',imagePaths[currentImage++]);if (currentImage >= imagePaths.length)currentImage = 0;showCanvasCtx.globalAlpha = 0.1;revealTimer = setInterval(revealImage,100);}function revealImage() {showCanvasCtx.save();showCanvasCtx.drawImage(img,0,0,600,400);showCanvasCtx.globalAlpha += 0.1;if (showCanvasCtx.globalAlpha >= 1.0)clearInterval(revealTimer);showCanvasCtx.restore();}</script></head><body><canvas id='showCanvas' width='600' height='400'>Canvas Not Supported</canvas></body></html>

一个简单的动画绘制：

<!DOCTYPE HTML><html><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Canvas Test With No Buffering</title><script type="text/javascript">var rectY=200, rectW=40;var rectX = -rectW;var canvas = null;var context = null;function init() {canvas = document.getElementById('testCanvas');context = canvas.getContext("2d");blank();context.fillStyle= "yellow";context.fillRect(rectX,rectY,rectW,rectW);setInterval(anim, 30);}function blank() {context.fillStyle = "#00ddee";context.fillRect(0,0,context.canvas.width, context.canvas.height);}function anim() {if (rectX < context.canvas.width) {blank();rectX += 5;context.fillStyle = "yellow";context.strokeStyle = "red";context.lineWidth = 3;context.fillRect(rectX,rectY,rectW,rectW);context.strokeRect(rectX,rectY,rectW,rectW);}else rectX=-rectW;}</script></head><body onload="init()"><canvas id="testCanvas" width="400" height="400">Canvas not supported</canvas></body></html>

加上双缓冲之后，画面不再闪烁：

<!DOCTYPE HTML><html><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Canvas Test Using Double Buffering</title><script type="text/javascript">var canvas = null;var context = null;var bufferCanvas = null;var bufferCanvasCtx = null;var flakeArray = [];var flakeTimer = null;var maxFlakes = 200;function Flake() {    this.x = Math.round(Math.random() * context.canvas.width);    this.y = -10;    this.drift = Math.random();    this.speed = Math.round(Math.random() * 5) + 1;    this.width = (Math.random() * 3) + 2;    this.height = this.width;}function init() {canvas = document.getElementById('testCanvas');context = canvas.getContext("2d");bufferCanvas = document.createElement("canvas");bufferCanvasCtx = bufferCanvas.getContext("2d");bufferCanvasCtx.canvas.width = context.canvas.width;bufferCanvasCtx.canvas.height = context.canvas.height;// initialize the rectsflakeTimer = setInterval(addFlake, 200);Draw();setInterval(animate, 30);}function addFlake() {    flakeArray[flakeArray.length] = new Flake();    if (flakeArray.length == maxFlakes)        clearInterval(flakeTimer);}function blank() {bufferCanvasCtx.fillStyle = "#330033";bufferCanvasCtx.fillRect(0,0,bufferCanvasCtx.canvas.width, bufferCanvasCtx.canvas.height);}function animate() {Update();Draw();}function Update() {    for (var i = 0; i < flakeArray.length; i++) {                    if (flakeArray[i].y < context.canvas.height) {                        flakeArray[i].y += flakeArray[i].speed;                        if (flakeArray[i].y > context.canvas.height)                            flakeArray[i].y = -5;                        flakeArray[i].x += flakeArray[i].drift;                        if (flakeArray[i].x > context.canvas.width)                            flakeArray[i].x = 0;                    }    }}function Draw(){context.save();/*// create a clipping regionbufferCanvasCtx.beginPath();bufferCanvasCtx.fillStyle="black";bufferCanvasCtx.fillRect(0,0,bufferCanvas.width,bufferCanvas.height);bufferCanvasCtx.arc(bufferCanvas.width/2,bufferCanvas.height/2,bufferCanvas.height/3,0,2*Math.PI);bufferCanvasCtx.clip();*/blank();for (var i = 0; i < flakeArray.length; i++) {    bufferCanvasCtx.fillStyle = "white";    bufferCanvasCtx.fillRect(flakeArray[i].x,flakeArray[i].y,flakeArray[i].width,flakeArray[i].height);}// copy the entire rendered image from the buffer canvas to the visible onecontext.drawImage(bufferCanvas, 0,0,bufferCanvas.width, bufferCanvas.height);context.restore();}</script></head><body onload="init()"><canvas id="testCanvas" width="800" height="800">Canvas not supported</canvas></body></html>

主要是通过以下代码创建了一个Canvas，之后将在这个Canvas上绘制完毕后拷贝到显示Canvas上。
bufferCanvas = document.createElement("canvas");
bufferCanvasCtx = bufferCanvas.getContext("2d");