var dom = document.getElementById("clock"); var ctx = dom.getContext("2d"); var width = ctx.canvas.width;
var height = ctx.canvas.height; var r = width / 2;function drawBackground(){ **ctx.save();**
.......省略一些代碼
}function drawHour(hour,minute){.......省略一些代碼}function drawMinute(minute,second){.......省略一些代碼}function drawSecond(second){ .......省略一些代碼
}function drawDot(){.......省略一些代碼} function draw(){
**ctx.clearRect(0,0,width,height);**
var time = new Date(), hour = time.getHours(),
minute = time.getMinutes(), second = time.getSeconds();
drawBackground();
drawHour(hour,minute);
drawMinute(minute,second);
drawSecond(second);
drawDot();
**ctx.restore();**
}
draw();
setInterval(draw,1000);為什么ctx.clearRect(0,0,width,height)要放在draw()函數(shù)第一行？那不是一調(diào)用就被清除了？那還怎么畫(huà)？
為什么這里的clearRect要放在第一行？
梵蒂岡之花
2018-09-14 10:09:58
