canvas基础绘制-绚丽倒计时的实例

 var WINDOW_WIDTH = 1024; var WINDOW_HEIGHT = 768; var RADIUS = 8; var MARGIN_TOP = 60; var MARGIN_LEFT = 30; var endTime = new Date();//const声明变量，不可修改，必须声明时赋值； endTime.setTime( endTime.getTime() + 3600*1000);//当前时间向后一小时； var curShowTimeSeconds = 0; var balls =[]; const colors = ["#33B5E5","#0099CC","#AA66CC","#9933CC","#99CC00","#669900","#FFBB33","#FF8800","#FF4444","#CC0000"]; window.onload = function () { //屏幕自适应 WINDOW_WIDTH = document.body.clientWidth; WINDOW_HEIGHT = document.body.clientHeight; RADIUS = Math.round(WINDOW_WIDTH*4/5/108)-1; MARGIN_TOP = Math.round(WINDOW_HEIGHT/5); MARGIN_LEFT = Math.round(WINDOW_WIDTH/10); var canvas = document.getElementById("canvas"); var context = canvas.getContext("2d"); canvas.width = WINDOW_WIDTH; canvas.height = WINDOW_HEIGHT; curShowTimeSeconds = getCurrentShowTimeSeconds(); setInterval( function () { update(); render(context); },50) }; function getCurrentShowTimeSeconds() { var curTime = new Date();//获取目前时间； var ret = endTime.getTime()-curTime.getTime(); ret = Math.round(ret/1000);//获取秒数差值； return ret>=0?ret:0; }

 function update() { var nextShowTimeSeconds = getCurrentShowTimeSeconds(); var nextHours = parseInt(nextShowTimeSeconds/3600); var nextMinutes = parseInt((nextShowTimeSeconds-nextHours*3600)/60); var nextSeconds = nextShowTimeSeconds%60; var curHours = parseInt(curShowTimeSeconds/3600); var curMinutes = parseInt((curShowTimeSeconds-curHours*3600)/60); var curSeconds = curShowTimeSeconds%60; if(nextSeconds!=curSeconds){ if(parseInt(curHours/10)!=parseInt(nextHours/10)){ addBalls(MARGIN_LEFT+0,MARGIN_TOP,parseInt(curHours/10)); } if(parseInt(curHours%10)!=parseInt(nextHours%10)){ addBalls(MARGIN_LEFT+15*(RADIUS+1),MARGIN_TOP,parseInt(curHours%10)); } if(parseInt(curMinutes/10)!=parseInt(nextMinutes/10)){ addBalls(MARGIN_LEFT+39*(RADIUS+1),MARGIN_TOP,parseInt(curMinutes/10)); } if(parseInt(curMinutes%10)!=parseInt(nextMinutes%10)){ addBalls(MARGIN_LEFT+54*(RADIUS+1),MARGIN_TOP,parseInt(curMinutes%10)); } if(parseInt(curSeconds/10)!=parseInt(nextSeconds/10)){ addBalls(MARGIN_LEFT+78*(RADIUS+1),MARGIN_TOP,parseInt(curSeconds/10)); } if(parseInt(curSeconds%10)!=parseInt(nextSeconds%10)){ addBalls(MARGIN_LEFT+93*(RADIUS+1),MARGIN_TOP,parseInt(curSeconds%10)); } curShowTimeSeconds = nextShowTimeSeconds; } updateBalls(); } function updateBalls() { //循环遍历每一个彩色动画小球 for(var i=0;i=WINDOW_HEIGHT){ balls[i].y = WINDOW_HEIGHT-RADIUS; balls[i].vy = -balls[i].vy*0.75; } } // 如果小球出了画布，就清除小球,性能优化 var cnt = 0; for(var i=0;i0&&balls[i].x+RADIUSMath.min(300,cnt)){ balls.pop(); } }

 function addBalls(x,y,num) { for (var i = 0; i