html5 canvas 画圆弧有锯齿怎么解决_随笔

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>

<title>canvasTest</title>

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>

canvas画出来的图片是位图，位图在放大的情况下是会模糊的，然而你所说的“缩放”应该是在canvas宽高固定后通过改变其style样式表进行放大缩小，当然图片是放大了，可是也模糊了，因为不是矢量图呀。

欢迎分享，转载请注明来源：内存溢出

html5 canvas 画圆弧有锯齿怎么解决