Html5 Canvas 畫橢圓有鋸齒：因為在Canvas中整數座標值對應的位置恰巧是螢幕象素點中間的夾縫，那麼當按這樣的座標進行線條渲染時所要用到的就是夾縫兩邊的象素點，這樣即便設定了lineWidth為1也將看到兩個象素效果的線條，解決方法原象素點+0.5進行偏移。
下面是處理前後的效果比較：
<!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) {
//序號、計數
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框架中針對ie載入canvas延時問題手動初始化物件
if (typeof G_vmlCanvasManager != "undefined") G_vmlCanvasManager.initElement(cvs);
//2D畫布物件
this.ctx = cvs.getContext("2d");
/* * 繪製線條
* @ops JSON物件，可按實際支援屬性擴充套件，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)"}); //普通線
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>
↓ 處理的 ↓ 普通的 ↓ +0.5偏移的<br />
</body>
</html>
Html5 Canvas 畫橢圓有鋸齒：因為在Canvas中整數座標值對應的位置恰巧是螢幕象素點中間的夾縫，那麼當按這樣的座標進行線條渲染時所要用到的就是夾縫兩邊的象素點，這樣即便設定了lineWidth為1也將看到兩個象素效果的線條，解決方法原象素點+0.5進行偏移。
下面是處理前後的效果比較：
<!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) {
//序號、計數
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框架中針對ie載入canvas延時問題手動初始化物件
if (typeof G_vmlCanvasManager != "undefined") G_vmlCanvasManager.initElement(cvs);
//2D畫布物件
this.ctx = cvs.getContext("2d");
/* * 繪製線條
* @ops JSON物件，可按實際支援屬性擴充套件，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)"}); //普通線
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>
↓ 處理的 ↓ 普通的 ↓ +0.5偏移的<br />
</body>
</html>