参考:HTML5与CSS3权威指南
或者W3Cschool 菜鸟教程之类的 都有详细的用法
context.beginPath();
context.arc(200,200,150,0,Math.PI*2,true);
context.closePath();
context.fillStyle=’rgba(255,255,255,0.7)’;
context.fill();
}
Canvas - 文本
使用 canvas 绘制文本,重要的属性和方法如下:
font - 定义字体
fillText(text,x,y) - 在 canvas 上绘制实心的文本
strokeText(text,x,y) - 在 canvas 上绘制空心的文本
createLinearGradient(x,y,x1,y1) - 创建线条渐变
createRadialGradient(x,y,r,x1,y1,r1) - 创建一个径向/圆渐变
当我们使用渐变对象,必须使用两种或两种以上的停止颜色。
addColorStop()方法指定颜色停止,参数使用坐标来描述,可以是0至1.
drawImage(image,x,y)
canvas.save() canvas.restore() 作用是两个相互匹配出现的,作用是用来保存画布的状态和取出保存的状态的。
rotate() 旋转
transplate() 平移
用canvas绘制一个可以展现实时时间的时钟
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>画时钟</title>
</head>
<body onload="draw('canvas')">
<canvas id="canvas" width="400px" height="400px" border:></canvas>
</body>
<script>
var dom=document.getElementById('canvas');
var cxt=dom.getContext("2d");
var width=cxt.canvas.width;
var height=cxt.canvas.height;
var r=width/2;
function drawBackground(){
cxt.save();
cxt.translate(r,r);
cxt.beginPath();
cxt.lineWidth=10;
cxt.arc(0,0,r-5,0,2*Math.PI,false);
cxt.stroke();
cxt.font="18px Arial";
cxt.textAlign='center'
cxt.textBaseline='middle'
var hourNums=[3,4,5,6,7,8,9,10,11,12,1,2];
hourNums.forEach(function(number,i){
var rad=2*Math.PI/12*i;
var x=Math.cos(rad)*(r-30);
var y=Math.sin(rad)*(r-30);
cxt.fillText(number,x,y);
});
for(var i=0;i<60;i++){
var rad=2*Math.PI/60*i;
var x=Math.cos(rad)*(r-18);
var y=Math.sin(rad)*(r-18);
cxt.beginPath();
if(i % 5===0){
cxt.fillStyle="#000"
cxt.arc(x,y,2,0,2*Math.PI,false);
}
else{
cxt.fillStyle="#ccc"
cxt.arc(x,y,2,0,2*Math.PI,false);
}
cxt.fill();
}
}
function drawHour(hour,minute){
cxt.save();
cxt.beginPath();
var rad=2*Math.PI/12*hour;
var mrad=2*Math.PI/12/60*minute
cxt.rotate(rad+mrad);
cxt.lineWidth=6;
cxt.lineCap='round'
cxt.moveTo(0,10);
cxt.lineTo(0,-r/2);
cxt.stroke();
cxt.restore();
}
function drawMinute(minute){
cxt.save();
cxt.beginPath();
var rad=2*Math.PI/60*minute;
cxt.rotate(rad);
cxt.lineWidth=3;
cxt.lineCap='round'
cxt.moveTo(0,10);
cxt.lineTo(0,-r+30);
cxt.stroke();
cxt.restore();
}
function drawSecond(second){
cxt.save();
cxt.beginPath();
cxt.fillStyle='#c14543'
var rad=2*Math.PI/60*second;
cxt.rotate(rad);
cxt.moveTo(-2,20);
cxt.lineTo(2,20);
cxt.lineTo(1,-r+18);
cxt.lineTo(-1,-r+18);
cxt.fill();
cxt.restore();
}
function drawDot(){
cxt.beginPath();
cxt.fillStyle='#fff'
cxt.arc(0,0,3,0,2*Math.PI,false);
cxt.fill();
}
function draw(){
cxt.clearRect(0,0,width,height);
var now=new Date();
var hour=now.getHours();
var minute=now.getMinutes();
var second=now.getSeconds();
drawBackground();
drawHour(hour,minute);
drawMinute(minute);
drawSecond(second);
drawDot();
cxt.restore();
}
draw();
setInterval(draw,1000);
</script>
</html>