我正在编写一个使用canvas旋转转速表指针的脚本。我对canvas不太熟悉,以下是我的代码:
function startup() {
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var meter = new Image();
meter.src = 'background.png';
var pin = new Image();
pin.src = 'needle.png';
context.drawImage(meter,0,0);
context.translate(275,297);
for (var frm = 0; frm < 6000; frm++){
var r=frm/1000; //handle here
var i=r*36-27; //angle of rotation from value of r and span
var angleInRadians = 3.14159265 * i/180; //converting degree to radian
context.rotate(angleInRadians); //rotating by angle
context.drawImage(pin,-250,-3); //adjusting pin center at meter center
}
}
以下是脚本的演示:
http://www.kingoslo.com/instruments/
问题在于,正如您所看到的那样,在每个for循环之间,红色指针没有被清除。
我需要做的是在每个循环周期中清除针对象的画布。我该怎么做呢?
谢谢。
顺祝商祺,
Marius