教学项目二十二 JavaScript中图片特效网页设计 【教学内容】 讲解JavaScript中几种图片特效网页设计 【教学目的】 使学生学会设计网页的图片特效 【教学重点】 图片特效的处理思想 【教学难点】 理解图片特效的处理方法 【教学方式】 讨论式、案例分析式、练习式相结合 【教学参考】 1．<<JavaScript 入门与提高>> 杨浩著 清华大学出版社 2．<<Internet 网页工场>> Wittime工作室 重庆出版社 3．<<JavaScript从入门到精通>> 电脑报社出版 4．<<JavaScript编程起步>> 人民邮电出版社 【教学过程】 【新课】 案例设计： 通过不断刷新，六张图片可以交替出现       分析： 先复制1.jpg 、 2.jpg、 3.jpg、 4.jpg、 5.jpg、 6.jpg到站点主目录下，通过刷新获取当前时间的秒钟数的不同，显示不同的图片。 程序代码如下： <html> <body> <script language="JavaScript"> var dt = new Date(); var hr = dt.getSeconds(); if (hr<=10) { hr=1;} if((hr<=20)&&(hr>10)) { hr=2;} if ((hr<=30)&&(hr>20)) { hr=3;} if ((hr<=40)&&(hr>30)) { hr=7;} if ((hr<=50)&&(hr>40)) { hr=8;} if ((hr<=60)&&(hr>50)) { hr=9;} var msg="<IMG SRC="+hr+".jpg>"; document.write(msg); </script> </body> </html> 案例设计： 设计网页中的落叶效果。  程序代码如下： <html> <head> <meta http-equiv="Content-Language" content="zh-cn"> <meta http-equiv="Content-Type" content="text/html; charset=gb2312"> <meta name="GENERATOR" content="Microsoft FrontPage 4.0"> <meta name="ProgId" content="FrontPage.Editor.Document"> </head> <body> <SCRIPT LANGUAGE="JavaScript1.2"> <!-- Begin var no = 12; // number of hearts var speed = 6; // smaller number moves the hearts faster var heart = "69.gif"; var flag; var ns4up = (document.layers) ? 1 : 0; // browser sniffer var ie4up = (document.all) ? 1 : 0; var dx, xp, yp; // coordinate and position variables var am, stx, sty; // amplitude and step variables var i, doc_width = 800, doc_height = 600; if (ns4up) { doc_width = self.innerWidth; doc_height = self.innerHeight; } else if (ie4up) { doc_width = document.body.clientWidth; doc_height = document.body.clientHeight; } dx = new Array(); xp = new Array(); yp = new Array(); amx = new Array(); amy = new Array(); stx = new Array(); sty = new Array(); flag = new Array(); for (i = 0; i < no; ++ i) { dx[i] = 0; // set coordinate variables xp[i] = Math.random()*(doc_width-30)+10; // set position variables yp[i] = Math.random()*doc_height; amy[i] = 12+ Math.random()*20; // set amplitude variables amx[i] = 10+ Math.random()*40; stx[i] = 0.02 + Math.random()/10; // set step variables sty[i] = 0.7 + Math.random(); // set step variables flag[i] = (Math.random()>0.5)?1:0; if (ns4up) { // set layers if (i == 0) { document.write("<layer name=\"dot"+ i +"\" left=\"15\" "); document.write("top=\"15\" visibility=\"show\"><img src=\""); document.write(heart+ "\" border=\"0\"></layer>"); } else { document.write("<layer name=\"dot"+ i +"\" left=\"15\" "); document.write("top=\"15\" visibility=\"show\"><img src=\""); document.write(heart+ "\" border=\"0\"></layer>"); } } else if (ie4up) { if (i == 0) { document.write("<div id=\"dot"+ i +"\" style=\"POSITION: "); document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: "); document.write("visible; TOP: 15px; LEFT: 15px;\"><img src=\""); document.write(heart+ "\" border=\"0\"></div>"); } else { document.write("<div id=\"dot"+ i +"\" style=\"POSITION: "); document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: "); document.write("visible; TOP: 15px; LEFT: 15px;\"><img src=\""); document.write(heart+ "\" border=\"0\"></div>"); } } } function snowNS() { // Netscape main animation function for (i = 0; i < no; ++ i) { // iterate for every dot if (yp[i] > doc_height-50) { xp[i] = 10+ Math.random()*(doc_width-amx[i]-30); yp[i] = 0; flag[i]=(Math.random()<0.5)?1:0; stx[i] = 0.02 + Math.random()/10; sty[i] = 0.7 + Math.random(); doc_width = self.innerWidth; doc_height = self.innerHeight; } if (flag[i]) dx[i] += stx[i]; else dx[i] -= stx[i]; if (Math.abs(dx[i]) > Math.PI) { yp[i]+=Math.abs(amy[i]*dx[i]); xp[i]+=amx[i]*dx[i]; dx[i]=0; flag[i]=!flag[i]; } document.layers["dot"+i].top = yp[i] + amy[i]*(Math.abs(Math.sin(dx[i])+dx[i])); document.layers["dot"+i].left = xp[i] + amx[i]*dx[i]; } setTimeout("snowNS()", speed); } function snowIE() { // IE main animation function for (i = 0; i < no; ++ i) { // iterate for every dot if (yp[i] > doc_height-50) { xp[i] = 10+ Math.random()*(doc_width-amx[i]-30); yp[i] = 0; stx[i] = 0.02 + Math.random()/10; sty[i] = 0.7 + Math.random(); flag[i]=(Math.random()<0.5)?1:0; doc_width = document.body.clientWidth; doc_height = document.body.clientHeight; } if (flag[i]) dx[i] += stx[i]; else dx[i] -= stx[i]; if (Math.abs(dx[i]) > Math.PI) { yp[i]+=Math.abs(amy[i]*dx[i]); xp[i]+=amx[i]*dx[i]; dx[i]=0; flag[i]=!flag[i]; } document.all["dot"+i].style.pixelTop = yp[i] + amy[i]*(Math.abs(Math.sin(dx[i])+dx[i])); document.all["dot"+i].style.pixelLeft = xp[i] + amx[i]*dx[i]; } setTimeout("snowIE()", speed); } if (ns4up) { snowNS(); } else if (ie4up) { snowIE(); } // End --> </script> <table border="0" width="99%" > <tr> <td width="100%"> <p align="center"><font size="6" face="楷体_GB2312" color="#0000FF">网页设计在线教程</font></td> </tr> <tr> <td width="100%">FLASH</td> </tr> <tr> <td width="100%"> <p align="left">HTML</td> </tr> <tr> <td width="100%">FRONTPAGE</td> </tr> <tr> <td width="100%">Dreamweaver</td> </tr> <tr> <td width="100%">CSS</td> </tr> <tr> <td width="100%">Fireworks</td> </tr> <tr> <td width="100%">Photoshop</td> </tr> </table><table border="0" width="94%"> <tr> <td width="100%"></td> <td width="100%"></td> </tr> <tr> <td width="200%" colspan="2"> <p align="center"><font size="5" face="宋体">COPYRIGHT @2003</font><font size="5" face="楷体_GB2312">湖北职院计科系学生网</font></td> </tr> <tr> <td width="200%" colspan="2"> <p align="center"><font size="5">Mailto: xgzyljj@163.net</font></td> </tr> </table> <p align="center">　</p> </body> </html> 案例设计： 设计背景图片下滚，文字上滚的网页特效。  程序代码如下： <html> <head> <bgsound src=liangzhu.mp3 loop=1> <SCRIPT language=JavaScript> //Author:redriver var index =15 text = new Array(14); text[0] ='&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;偶然 ' text[1] ='' text[2] ='&nbsp; 汪国真 ' text[3] ='' text[4] ='我是天空里的一片云，' text[5] ='偶尔投影在你的波心——' text[6] ='你不必诧异,' text[7] ='更无须欢喜——' text[8] ='在转瞬间消灭了踪影。' text[9] ='' text[10] ='你我相逢在黑暗的海上，' text[11] ='你有你的，我有我的，方向； ' text[12] ='你记得也好， ' text[13] ='最好你忘掉， ' text[14] ='在这交汇时互放的光亮！ ' document.write ("<p align=center><marquee scrollamount='1' scrolldelay='60' direction= 'UP' width='550 ' id=xiaoqing height='200' onmouseover=xiaoqing.stop() onmouseout=xiaoqing.start()>"); for (i=0;i<index;i++){ document.write ("<B><font face=隶书 color=#00ee00 size=7>"); document.write (text[i] + "</font></B><br>"); } document.write ("</marquee>"); documetn.write("</p>"); </SCRIPT> </head> <body background="8.jpg"> <script language="JavaScript"> <!-- Begin var backgroundOffset = 0; var bgObject = eval('document.body'); function scrollBG(maxSize) { backgroundOffset = backgroundOffset + 1; if (backgroundOffset > maxSize) backgroundOffset = 0; bgObject.style.backgroundPosition = "0 " + backgroundOffset; } var ScrollTimer = window.setInterval("scrollBG(307)", 64); // End --> </script> </body> </html> 【课后小结】 本例中的图片特效程序比较有代表性，要求能够掌握通过修改给定的源代码，实现满足用户要求的特效网页。