Html5 Canvas 画椭圆有锯齿：因为在Canvas中整数坐标值对应的位置恰巧是屏幕象素点中间的夹缝，那么当按这样的坐标进行线条渲染时所要用到的就是夹缝两边的象素点，这样即便设置了lineWidth为1也将看到两个象素效果的线条，解决方法原象素点+0.5进行偏移。
下面是处理前后的效果比较：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html>
<head>
<meta http-equiv="Content-Type" content="text/html charset=utf-8">
<title>canvasTest</title>
<script type="text/javascript" src="http://www.pyzy.net/Demo/html5_cancas_js/excanvas.js"></script>
<script type="text/javascript">
var MyCanvas = function(boxObj, width, height) {
//序号、计数
this.index = arguments.callee.prototype.Count = (arguments.callee.prototype.Count || 0) + 1
var cvs = document.createElement("canvas")
cvs.id = "myCanvas" + this.index
cvs.width = width || 800
cvs.height = height || 600
(boxObj || document.body).appendChild(cvs)
//excanvas框架中针对ie加载canvas延时问题手动初始化对象
if (typeof G_vmlCanvasManager != "undefined") G_vmlCanvasManager.initElement(cvs)
//2D画布对象
this.ctx = cvs.getContext("2d")
/* * 绘制线条
* @ops JSON对象，可按实际支持属性扩展，示例： { lineWidth:1,strokeStyle:'rgb(255,255,255)' }
* @dotXY:{ x:0, y:0 } ||[{ x:0, y:0 },{ x:0, y:0 }]
*/
this.drawLine = function(dotXY, ops) {
this.ctx.beginPath()
for (var att in ops) this.ctx[att] = ops[att]
dotXY = dotXY.constructor == Object ? [dotXY || { x: 0, y: 0}] : dotXY
this.ctx.moveTo(dotXY[0].x, dotXY[0].y)
for (var i = 1, len = dotXY.length i < len i++) this.ctx.lineTo(dotXY[i].x, dotXY[i].y)
this.ctx.stroke()
}
}
window.onload=function(){
var c1 = new MyCanvas()
c1.drawLine([{ x: 10, y: 10 }, { x: 10, y: 200 }],{lineWidth:2,strokeStyle:'rgb(0,0,0)'})
c1.drawLine([{ x: 11, y: 10 }, { x: 11, y: 200 }],{lineWidth:2,strokeStyle:'rgb(255,255,255)'})
c1.drawLine([{ x: 100, y: 10 }, { x: 100, y: 200 }],{lineWidth:1,strokeStyle:'rgb(0,0,0)'}) //普通线
c1.drawLine([{ x: 200.5, y: 10 }, { x: 200.5, y: 200 }],{lineWidth:1,strokeStyle:'rgb(0,0,0)'}) //+0.5偏移
}
</script>
</head>
<body>
↓ 处理的↓ 普通的↓ +0.5偏移的<br />
</body>
</html>
sx和sy是个比例数字，比如设置scale(2,2)，是在x方向和y方向都放大了两倍，出来的效果就是图像的缩放。画布的位置并没有改变。你这样理解，scale是把坐标改变了相应的比例。还是以scale(2,2)为例。为了显示明显，给段css,
<!doctype html><html lang="en">
<head>
<meta charset="UTF-8">
<title>锯齿图</title>
<script type="text/javascript">
window.addEventListener("load", eventWindowLoaded, false)
function eventWindowLoaded(){
var x,y
var theCanvas = document.getElementById("canvas")
var context = theCanvas.getContext("2d")
//context.fillStyle = "#000000"
//context.fillStyle = '#EEEEEE'
//context.fillRect(0, 0, theCanvas.width, theCanvas.height)
//Box
context.strokeStyle = '#000000'
context.lineWidth=10
context.strokeRect(0, 0, theCanvas.width-0, theCanvas.height-0)
context.fillStyle = "#000000"
for(x=5x<=canvas.widthx=x+10){
context.beginPath()
context.arc(x,5,5,0,Math.PI*2,true)
context.arc(x,canvas.height-5,5,0,Math.PI*2,true)
context.closePath()
context.fill()
}
for(y=5y<=canvas.heighty=y+10){
context.beginPath()
context.arc(5,y,5,0,Math.PI*2,true)
context.arc(canvas.width-5,y,5,0,Math.PI*2,true)
context.closePath()
context.fill()
}
}
</script>
</head>
<body>
<div style="position: absolutetop: 0pxleft: 0px">
<canvas id="canvas" width="200" height="200" top=50pxleft=50px>
</div>
</body>
</html>
代码运行出来就是
本人QQ812397704
