Canvas API中的drawImage方法,下面对此方法略做介绍。 在Canvas API中绘制图">
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HTML5编程实战之二-使用动画的形式切换图片代码案例

时间:2021-07-01 10:21:17 帮助过:23人阅读

本文主要用到的知识

  本文主要用到了http://www.gxlcms.com/code/7892.html" target="_blank">Canvas API中的drawImage方法,下面对此方法略做介绍。

  在Canvas API中绘制图像用drawImage方法,这是一个重载方法,定义如下:

context.drawImage(image,x,y);
context.drawImage(image,x,y,w,h);
context.drawImage(image,sx,sy,sw,sh,dx,dy,dw,dh);

  第一个方法有三个参数,第一个参数为要绘制的图像(还可以是video元素),x和y为该图像在画布中的起始坐标。

  第二个方法有五个参数,前三个跟第一个方法意义一样,w和h指绘制时的图像宽度和高度,可以用来进行图像缩放。

  第三个方法有九个参数,第一个参数跟前二个方法意义相同,后八个参数中前四个在源图像上一取一个矩形,后四个参数用于在画布上定义一个矩形,整个方法的作用就是把源图像上部分区域(第二到五个参数定义的部分)复制到画布上(后四个参数定义的部分)。

  本文主要利用了第三个方法完成绘制。

源代码

<!DOCTYPE html><html><head>
    <meta charset="UTF-8">
    <title>用动画的形式切换图片</title>
    <script type="text/javascript">
        var width, height;        
        var context, image, functionId;        
        var drawLeft, drawWidth;        
        var drawTop, drawHeight;        
        var spaceWidth, spaceHeight;        
        var speed=5000;        
        var images = ["http://i.6.cn/cvbnm/4e/7e/bb/75f251a8e2ae935d598f17b4f8275060.jpg", 
        "http://i.6.cn/cvbnm/4a/6e/fb/805175016e502c483b75276f29801df3.jpg", 
        "http://i.6.cn/cvbnm/6a/72/18/1787a3b2754ef48e374bbd14635f5c36.jpg", 
        "http://i.6.cn/cvbnm/94/55/6c/b1ba743ba617be2891fa06b67d795511.jpg", 
        "http://i.6.cn/cvbnm/02/1b/04/8018ee9e5756ac6b30f27d7ad6396b03.jpg", 
        "http://i.6.cn/cvbnm/85/ea/d1/65f15857b971afb3b6e38b5fcdadc9c0.jpg"];        
        function selectFrom(iFirstValue, iLastValue) {            
        var iChoices = iLastValue - iFirstValue + 1;            
        return Math.floor(Math.random() * iChoices + iFirstValue);
        }        function showPicture(effects) {            
        var count = 0;            
        for (var o in effects) {
                count++;
            }           
             var canvas = document.getElementById('canvas');
            context = canvas.getContext('2d');
            width = canvas.width;
            height = canvas.height;            
            var currImage = 0;
            image = new Image();
            image.src = images[currImage];
            context.drawImage(image, 0, 0, width, height);
            currImage++;            
            if (count > 0) {
                setInterval(function () {                    
                var rand =  selectFrom(0, count - 1);
                    image.src = images[currImage];
                    currImage++;                    
                    if (currImage == images.length) {
                        currImage = 0;
                    }                    
                    var index = 0;                    
                    for (var effect in effects) {                        
                    if (index++ == rand) {
                            effects[effect]();                            
                            break;
                        }
                    }
                }, speed);
            }
        }

        window.onload=function(){
            showPicture({
                leftToRight: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    drawWidth = 0;
                    functionId = self.setInterval("drawleftToRight()", 10);
                },
                topToBottom: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    drawHeight = 0;
                    functionId = self.setInterval("drawtopToBottom()", 10);
                },
                hcenter: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    drawLeft = width / 2;
                    drawWidth = 0;
                    functionId = self.setInterval("drawhcenter()", 10);
                },
                vcenter: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    drawTop = height / 2;
                    drawHeight = 0;
                    functionId = self.setInterval("drawvcenter()", 10);
                },
                hwindow: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    spaceWidth = width / 10;
                    drawWidth = 0;
                    functionId = self.setInterval("drawhwindow()", 50);
                },
                vwindow: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    spaceHeight = height / 10;
                    drawHeight = 0;
                    functionId = self.setInterval("drawvwindow()", 50);
                },
                hvwindow: function () {
                    context.fillStyle = "#EEEEFF";
                    context.fillRect(0, 0, width, height);
                    spaceHeight = height / 10;
                    spaceWidth = width / 10;
                    drawWidth = 0;
                    drawHeight = 0;
                    functionId = self.setInterval("drawhvwindow()", 50);
                }
            });
        }        function drawleftToRight() {
            context.drawImage(image, 0, 0, drawWidth, image.height, 0, 0, drawWidth, image.height);
            drawWidth = drawWidth + 2;            
            if (drawWidth > width) {
                window.clearInterval(functionId);
            }
        }        function drawtopToBottom() {
            context.save();
            context.drawImage(image, 0, 0, image.width, drawHeight, 0, 0, image.width, drawHeight);
            drawHeight = drawHeight + 2;            
            if (drawHeight > height) {
                window.clearInterval(functionId);
            }
            context.restore();
        }        
        function drawhcenter() {
            context.save();
            context.drawImage(image, drawLeft, 0, drawWidth, image.height, drawLeft, 0, drawWidth, image.height);
            drawLeft = drawLeft - 1;
            drawWidth = drawWidth + 2;            
            if (drawLeft <= 0) {
                window.clearInterval(functionId);
            }
            context.restore();
        }        
        function drawvcenter() {
            context.save();
            context.drawImage(image, 0, drawTop, image.width, drawHeight, 0, drawTop, image.width, drawHeight);
            drawTop = drawTop - 1;
            drawHeight = drawHeight + 2;            
            if (drawTop <= 0) {
                window.clearInterval(functionId);
            }
            context.restore();
        }        function drawhwindow() {            
        for (i = 0; i < 10; i++) {
                context.drawImage(image, 0 + i * spaceWidth, 0, drawWidth, 
                image.height, 0 + i * spaceWidth, 0, drawWidth, image.height);
            }
            drawWidth += 1;            
            if (drawWidth - 1 > spaceWidth) {
                window.clearInterval(functionId);
            }
        }        function drawvwindow() {
            context.save();
            context.clearRect(0, 0, width, height);            
            for (i = 0; i < 10; i++) {
                context.drawImage(image, 0, 0 + i * spaceHeight, image.width, 
                drawHeight, 0, 0 + i * spaceHeight, image.width, drawHeight);
            }
            drawHeight += 1;            
            if (drawHeight - 1 > spaceHeight) {
                window.clearInterval(functionId);
            }
            context.restore();
        }        function drawhvwindow() {
            context.save();
            context.clearRect(0, 0, width, height);            
            for (i = 0; i < 10; i++) {                
            for (j = 0; j < 10; j++) {
                    context.drawImage(image, 0 + j * spaceWidth, 0 + i * 
                    spaceHeight, drawWidth, drawHeight, 0 + j * spaceWidth, 0 + i * 
                    spaceHeight, drawWidth, drawHeight);
                }
            }
            drawHeight += height / width;
            drawWidth += 1;            
            if (drawHeight > spaceHeight) {
                context.drawImage(image, 0, 0, width, height);
                window.clearInterval(functionId);
            }
            context.restore();
        }    </script></head><body>
    <h1>用动画的形式切换图片</h1>
    <canvas id="canvas" width="192px" height="255px"></canvas></body></html>

代码解析

  drawleftToRight():效果为从左向右显示,主要把第四个参数和第八个参数从0逐渐增加到图片的宽度

  drawtopToBottom():效果为从上向下显示,主要把第五个参数和第九个参数从0逐渐增加到图片的高度

  drawhcenter():效果为从中间水平向两边显示,主要把第二、六个参数从图像宽度的一半减小到0,第四、八个参数从0增加到图像宽度

  drawvcenter():效果为从中间向上下两边显示,跟上一个类似

  drawhwindow():效果为水平方向百叶窗,跟drawhcenter方法原理类似,只是这里是从多个地方进行的

  drawvwindow():效果为垂直方面百叶窗,跟drawvcenter方法原理类似,只是这里是从多个地方进行的

  drawhvwindow():效果为百叶窗,是drawhwindow()跟drawvwindow()的组合

  欢迎大家补充和完善。

  由于图片是放在其他网站上,所以加载比较慢,显的不是那么流畅,大家使用时可以换为本地图片,效果更佳。

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