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為什么直接使用setInterval(getCurrentShowTimeSeconds(),50)不行？

如題？這節(jié)課的原理到底是啥？按道理，直接設(shè)置定時器那不就會動了嗎？

正在回答

5 回答

老師前面就說過，setInterval()中的兩個函數(shù)，是一個設(shè)置動畫的基本框架。多年的開發(fā)經(jīng)驗。。。。。。。

0 回復(fù) 有任何疑惑可以回復(fù)我~

尼瑪。。。原來還有一句，

canvas clearRect() 方法

。。。。可我還是不懂老師為什么要那樣寫

0 回復(fù) 有任何疑惑可以回復(fù)我~ 
<!DOCTYPE?html>
<html>

	<head>
		<meta?charset="UTF-8">
		<title></title>
	</head>
	<script?type="text/javascript"?src="digit.js"></script>
	<script?type="text/javascript"?src="my_1.js"></script>
	<body>
		<canvas?id="canvas"?style="border:?1px?solid?gray;margin:?50px?auto;display:?block;">
			當(dāng)前瀏覽器不支持Canvas，請更換瀏覽器再試
		</canvas>
	</body>

</html>
var?r=6;
var?wd=120;
var?showtime;

const?endTime=new?Date(2016,6,14,18,47,52);

window.onload=function(){
	var?canvas=document.getElementById("canvas");
	var?context=canvas.getContext("2d");
	
	canvas.height=768;
	canvas.width=1366;
	setInterval(function(){
		MyTime(context)
	}
	,50);
	
}

function?MyTime(ct){
	var?nowtime=new?Date();
	var?showtime=endTime.getTime()-nowtime.getTime();
	if(showtime<=0){
		showtime=0;
	}
	showtime=Math.round(showtime/1000);
	
	var?hours=parseInt(showtime/3600),
		minutes=parseInt((showtime/60)%60),
		seconds=parseInt(showtime%60);
		console.log('一'+hours);
		console.log('二'+minutes);
		console.log('三'+seconds);
	
	mycanvas(0,0,ct,parseInt(hours/10));
	mycanvas(wd,0,ct,parseInt(hours%10));
	
	mycanvas(wd*2,0,ct,10);
	
	mycanvas(wd*3,0,ct,parseInt(minutes/10));
	mycanvas(wd*4,0,ct,parseInt(minutes%10));
	
	mycanvas(wd*5,0,ct,10);
	
	mycanvas(wd*6,0,ct,parseInt(seconds/10));
	mycanvas(wd*7,0,ct,parseInt(seconds%10));
}

function?mycanvas(X,Y,ct,num){
	ct.fillStyle='red';
	for(var?y=0;y<digit[num].length;y++)
		for(var?x=0;x<digit[num][y].length;x++){
			if(digit[num][y][x]==1){
				ct.beginPath();
				ct.arc(X+x*(r+2)*2+(r+2),Y+y*(r+2)*2+(r+2),r,0,2*Math.PI);
				ct.closePath();
				ct.fill();
			}
		}
}


0 回復(fù) 有任何疑惑可以回復(fù)我~

不對。。。其實也可以。。。我自己寫錯了，可新的問題就是，隨著時間變化，畫布被填滿了。。。


0 回復(fù) 有任何疑惑可以回復(fù)我~ 
var?WINDOW_WIDTH?=?1024;
var?WINDOW_HEIGHT?=?768;
var?RADIUS?=?8;
var?MARGIN_TOP?=?60;
var?MARGIN_LEFT?=?30;

const?endTime?=?new?Date(2014,6,11,18,47,52);
var?curShowTimeSeconds?=?0

window.onload?=?function(){

????var?canvas?=?document.getElementById('canvas');
????var?context?=?canvas.getContext("2d");

????canvas.width?=?WINDOW_WIDTH;
????canvas.height?=?WINDOW_HEIGHT;

????curShowTimeSeconds?=?getCurrentShowTimeSeconds()
????setInterval(
????????function(){
????????????render(?context?);
????????????update();
????????}
????????,
????????50
????);
}

function?getCurrentShowTimeSeconds()?{
????var?curTime?=?new?Date();
????var?ret?=?endTime.getTime()?-?curTime.getTime();
????ret?=?Math.round(?ret/1000?)

????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?){

????????curShowTimeSeconds?=?nextShowTimeSeconds;
????}
}

function?render(?cxt?){

????cxt.clearRect(0,0,WINDOW_WIDTH,?WINDOW_HEIGHT);

????var?hours?=?parseInt(?curShowTimeSeconds?/?3600);
????var?minutes?=?parseInt(?(curShowTimeSeconds?-?hours?*?3600)/60?)
????var?seconds?=?curShowTimeSeconds?%?60

????renderDigit(?MARGIN_LEFT?,?MARGIN_TOP?,?parseInt(hours/10)?,?cxt?)
????renderDigit(?MARGIN_LEFT?+?15*(RADIUS+1)?,?MARGIN_TOP?,?parseInt(hours%10)?,?cxt?)
????renderDigit(?MARGIN_LEFT?+?30*(RADIUS?+?1)?,?MARGIN_TOP?,?10?,?cxt?)
????renderDigit(?MARGIN_LEFT?+?39*(RADIUS+1)?,?MARGIN_TOP?,?parseInt(minutes/10)?,?cxt);
????renderDigit(?MARGIN_LEFT?+?54*(RADIUS+1)?,?MARGIN_TOP?,?parseInt(minutes%10)?,?cxt);
????renderDigit(?MARGIN_LEFT?+?69*(RADIUS+1)?,?MARGIN_TOP?,?10?,?cxt);
????renderDigit(?MARGIN_LEFT?+?78*(RADIUS+1)?,?MARGIN_TOP?,?parseInt(seconds/10)?,?cxt);
????renderDigit(?MARGIN_LEFT?+?93*(RADIUS+1)?,?MARGIN_TOP?,?parseInt(seconds%10)?,?cxt);
}

function?renderDigit(?x?,?y?,?num?,?cxt?){

????cxt.fillStyle?=?"rgb(0,102,153)";

????for(?var?i?=?0?;?i?<?digit[num].length?;?i?++?)
????????for(var?j?=?0?;?j?<?digit[num][i].length?;?j?++?)
????????????if(?digit[num][i][j]?==?1?){
????????????????cxt.beginPath();
????????????????cxt.arc(?x+j*2*(RADIUS+1)+(RADIUS+1)?,?y+i*2*(RADIUS+1)+(RADIUS+1)?,?RADIUS?,?0?,?2*Math.PI?)
????????????????cxt.closePath()

????????????????cxt.fill()
????????????}
}


0 回復(fù) 有任何疑惑可以回復(fù)我~

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