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I used HTML5 to make a flash-like animation of a small ball moving, but I encountered a strange problem... The source code is as follows:
<!DOCTYPE html><head><meta charset=utf-8><title>瞎玩呗</title><script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script></head><body><canvas id="canvas2" width="400" height="200"></canvas><script type="text/javascript">var c=document.getElementById("canvas2");var c2=c.getContext("2d");var width = 400;var height = 200; var qidian=0; //设置线条起点 var exp=1; //设置线条每次移动像 c2.strokeStyle = "rgba(255,0,0,1)"; function jump(){c2.clearRect(0,0,400,200)c2.fillStyle="FF0000";c2.beginPath();c2.arc(180,qidian,20,0,Math.PI*2,1); c2.closePath();c2.fill(); qidian=qidian+exp; //起点+活动像素位置 if(qidian==0 || qidian==height-1){ //判断当前线的位置,控制在区域内 exp=exp*-1; //乘以负一用来调整线路方向 } }</script><input onclick="interval=setInterval(jump,1);" value="开始" type="button"/><input onclick="clearInterval(interval);"value="停止" type="button"/></body></html>
if(qidian==0 || qidian== height-1){ // Determine the position of the current line , controlled within the area
Because your height is a variable. If it is not defined before, this will report an error and will not be executed. Change it to if (qidian==0 || qidian==200-1){ It is also possible var width = 400; This can be commented out because you didn't use this variable
Wow...a very simple question...I didn't notice it, it was too careless. Thank you very much~!