excanvas饼图实现

代码比较简单，需要注意的一点就是：
如果想让饼图的边框显示出来，需要找到excanvas.js中的contextPrototype.stroke方法，将其最后一行代码注释掉
contextPrototype.stroke = function(aFill) {
//  this.currentPath_ = [];
};

使用了extjs的组件生命周期，如果不采用extjs也很简单，将所有extjs的方法自行实现即可
代码如下：

Ext.ns('Ext.ux');
Ext.ux.pieChart = Ext.extend(Ext.BoxComponent, {
    circleX : 0,
    circleY : 0,
    data : undefined,
    labels : [],
    labelX : 0,
    labelY : 0,
    radius : 100,
    onRender : function(ct, position) {
        this.base(ct, position);
        this.ct = Ext.get(ct);    
        this.createCanvas(ct);
    },
    afterRender : function() {
        this.base(arguments);
        var context = this.ctx;
        this.drawCircle(context);
    },
    createCanvas : function(ct) {
        var canvas = document.createElement("canvas");
        this.ct.dom.appendChild(canvas);
        this.el = Ext.get(canvas);
        if (Ext.isIE && G_vmlCanvasManager)
            this.el = Ext.get(G_vmlCanvasManager.initElement(canvas));
        this.setCanvasSize(this.width, this.height);
        this.canvas = Ext.getDom(this.el);
        this.el.position('absolute', this.zIndex);
        this.ctx = this.getContext();
    },
    drawCircle : function(ctx) {
        this.shadow ? this.makeShadow() : '';
        var total = 0;
        for (var i = 0; i < this.data.length; i++)
            total += this.data[i][1];
        this.startangle = -Math.PI / 2;// canvas 的arc采用PI方式的角度进行计算，2PI表示360°
        ctx.lineWidth = 2;
        ctx.strokeStyle = "black";
        for (var i = 0; i < this.data.length; i++) {// 画每块扇片及其说明
            var d = this.data[i];
            this.endangle = this.startangle + d[1] / total * Math.PI * 2;
            ctx.beginPath();
            ctx.moveTo(this.circleX, this.circleY);// 画扇片
            ctx.arc(this.circleX, this.circleY, this.radius,
                    this.startangle, this.endangle, false);
            ctx.closePath();
            ctx.fillStyle = d[2];
            ctx.fill();
            ctx.stroke();
            this.startangle = this.endangle;
            
            ctx.fillStyle = d[2];// 画说明
            ctx.fillRect(this.labelX, this.labelY + 30 * i, 20, 20);
            ctx.strokeRect(this.labelX, this.labelY + 30 * i, 20, 20);
            var label = Ext.get(this.ct).createChild();// 扇形的文字说明
            label.position('absolute');
            label.setLeftTop(this.labelX + 30, this.labelY + 30 * i - 4);
            label.dom.innerHTML = this.labels[i] || d[0];
        }
    },
    makeShadow : function() {
        var c = {
            x : this.circleX,
            y : this.circleY,
            r : this.radius
        }
        //this.ctx.beginPath(); 当this.ctx.currentPath_中不存在任何元素时，就可以不调用beginPath
        this.ctx.arc(c.x + 5, c.y + 5, c.r, 0, Math.PI * 2, false)
        this.ctx.closePath();
        var radgrad = this.ctx.createRadialGradient(c.x + 5, c.y + 5, 0, c.x
                + 5, c.y + 5, c.r);
        radgrad.addColorStop(0, '#555555');
        this.ctx.fillStyle ='#555555';
        this.ctx.fill();
    },
    getContext : function() {
        return this.el.dom.getContext("2d");
    },

    setCanvasSize : function(w, h) {
        
        this.el.set( {
            width : w,
            height : h
        });
    }
});
Ext.onReady(function() {
    var pie = new Ext.ux.pieChart( {
        width : 600,
        height : 400,
        shadow : true,
        data : [['North', 12, 'red'], ['South', 23, 'blue'],
                ['East', 34, 'yellow'], ['West', 45, 'green']],
        circleX : 200,
        circleY : 200,
        labelX : 400,
        labelY : 100,
        radius : 150
    });
    pie.render(Ext.getBody());
});

contextPrototype.stroke = function(aFill) {
  this.currentPath_ = [];
};的效果

contextPrototype.stroke = function(aFill) {
  // this.currentPath_ = [];
};的效果