运用js绘制SVG图片

/**
 * Create an <svg> element and draw a pie chart into it.
 * 创建一个<svg>元素，并在其中绘制一个饼状图
 * Arguments:
 * 参数：
 *   data: an array of numbers to chart, one for each wedge of the pie.
 *   data：用于绘制数据的类型数组，数组的每一项都表示饼状图的一个部分
 *   width,height: the size of the SVG graphic, in pixels
 *   width，height：图形的长宽
 *   cx, cy, r: the center and radius of the pie
 *   cx, cy, r: 圆心和半径
 *   colors: an array of HTML color strings, one for each wedge
 *   colors: 包含颜色的数组，每种颜色代表了每个部分的颜色
 *   labels: an array of labels to appear in the legend, one for each wedge
 *   labels: 一个标签数组，每个部分的信息说明
 *   lx, ly: the upper-left corner of the chart legend
 * Returns: 
 *   lx，ly: 饼状图的左上角
 *    An <svg> element that holds the pie chart.
 *    一个保存<svg>的元素
 *    The caller must insert the returned element into the document.
 *     调用者必须将返回的元素插入到文档中
 */
function pieChart(data, width, height, cx, cy, r, colors, labels, lx, ly) {
    // This is the XML namespace for svg elements
    var svgns = "http://www.w3.org/2000/svg";    // Create the <svg> element, and specify pixel size and user coordinates
    var chart = document.createElementNS(svgns, "svg:svg");
    chart.setAttribute("width", width);
    chart.setAttribute("height", height);
    chart.setAttribute("viewBox", "0 0 " + width + " " + height);

    // Add up the data values so we know how big the pie is
    var total = 0;
    for(var i = 0; i < data.length; i++) total += data[i];

    // Now figure out how big each slice of pie is. Angles in radians.
    var angles = []
    for(var i = 0; i < data.length; i++) angles[i] = data[i]/total*Math.PI*2;

    // Loop through each slice of pie.
    startangle = 0;
    for(var i = 0; i < data.length; i++) {
        // This is where the wedge ends
        var endangle = startangle + angles[i];

        // Compute the two points where our wedge intersects the circle
        // These formulas are chosen so that an angle of 0 is at 12 o'clock
        // and positive angles increase clockwise.
        var x1 = cx + r * Math.sin(startangle);
        var y1 = cy - r * Math.cos(startangle);
        var x2 = cx + r * Math.sin(endangle);
        var y2 = cy - r * Math.cos(endangle);

        // This is a flag for angles larger than than a half circle
        // It is required by the SVG arc drawing component
        var big = 0;
        if (endangle - startangle > Math.PI) big = 1;

        // We describe a wedge with an <svg:path> element
        // Notice that we create this with createElementNS()
        var path = document.createElementNS(svgns, "path");

        // This string holds the path details
        var d = "M " + cx + "," + cy +  // Start at circle center
            " L " + x1 + "," + y1 +     // Draw line to (x1,y1)
            " A " + r + "," + r +       // Draw an arc of radius r
            " 0 " + big + " 1 " +       // Arc details...
            x2 + "," + y2 +             // Arc goes to to (x2,y2)
            " Z";                       // Close path back to (cx,cy)

        // Now set attributes on the <svg:path> element
        path.setAttribute("d", d);              // Set this path 
        path.setAttribute("fill", colors[i]);   // Set wedge color
        path.setAttribute("stroke", "black");   // Outline wedge in black
        path.setAttribute("stroke-width", "2"); // 2 units thick
        chart.appendChild(path);                // Add wedge to chart

        // The next wedge begins where this one ends
        startangle = endangle;

        // Now draw a little matching square for the key
        var icon = document.createElementNS(svgns, "rect");
        icon.setAttribute("x", lx);             // Position the square
        icon.setAttribute("y", ly + 30*i);
        icon.setAttribute("width", 20);         // Size the square
        icon.setAttribute("height", 20);
        icon.setAttribute("fill", colors[i]);   // Same fill color as wedge
        icon.setAttribute("stroke", "black");   // Same outline, too.
        icon.setAttribute("stroke-width", "2");
        chart.appendChild(icon);                // Add to the chart

        // And add a label to the right of the rectangle
        var label = document.createElementNS(svgns, "text");
        label.setAttribute("x", lx + 30);       // Position the text
        label.setAttribute("y", ly + 30*i + 18);
        // Text style attributes could also be set via CSS
        label.setAttribute("font-family", "sans-serif");
        label.setAttribute("font-size", "16");
        // Add a DOM text node to the <svg:text> element
        label.appendChild(document.createTextNode(labels[i]));
        chart.appendChild(label);               // Add text to the chart
    }

    return chart;
}