如何使用pdfbox绘制饼图？

Question

我必须使用 pdfbox 绘制饼图。

设数据为：

学科分数百分比分数累积度数
子 1 80 80 80
子 2 70 70 150
子 3 65 65 215
子 4 90 90 305
子 5 55 55 360

设半径和中心为 100 像素和 ( 250, 400)。

让我们取平行于 x 轴的初始线。
绘图初始行语句将是：
contentStream.drawLine(250, 400, 350, 400);

我坚持了下来：
a) 找到圆上点的 x, y 坐标，该点与初始线相距一定程度以绘制半径
b) 用贝塞尔曲线在两点之间画圆弧

如能提供解决问题的帮助，我们将不胜感激！

Answer 1

根据角度在圆上找到 x、y 坐标是学校数学，即 sin() 和 cos()，棘手的部分是用贝塞尔曲线绘制圆弧。

这里有一些代码可以绘制您要求的饼图。请注意，createSmallArc() 只能用于最大 90° 的角度。如果你想要更多，你要么必须通过绘制几个圆弧来修改代码，直到你回到 (0,0)，或者只绘制几个切片。

(createSmallArc() 由 Hans Muller, license: Creative Commons Attribution 3.0. Changes made: implemented original AS code into java. Algorithm is by Aleksas Riškus)

public class PieChart
{
    public static void main(String[] args) throws IOException
    {
        PDDocument doc = new PDDocument();
        PDPage page = new PDPage();
        doc.addPage(page);
        PDPageContentStream cs = new PDPageContentStream(doc, page);
        
        cs.transform(Matrix.getTranslateInstance(250, 400));
        
        cs.setNonStrokingColor(Color.yellow);
        drawSlice(cs, 100, 0, 80);
        cs.fill();
        cs.setNonStrokingColor(Color.red);
        drawSlice(cs, 100, 80, 150);
        cs.fill();
        cs.setNonStrokingColor(Color.green);
        drawSlice(cs, 100, 150, 215);
        cs.fill();
        cs.setNonStrokingColor(Color.blue);
        drawSlice(cs, 100, 215, 305);
        cs.fill();
        cs.setNonStrokingColor(Color.ORANGE);
        drawSlice(cs, 100, 305, 360);
        cs.fill();
        
        cs.close();
        doc.save("piechart.pdf");
        doc.close();
    }

    private static void drawSlice(PDPageContentStream cs, float rad, float startDeg, float endDeg) throws IOException
    {
        cs.moveTo(0, 0);
        List<Float> smallArc = createSmallArc(rad, Math.toRadians(startDeg), Math.toRadians(endDeg));
        cs.lineTo(smallArc.get(0), smallArc.get(1));
        cs.curveTo(smallArc.get(2), smallArc.get(3), smallArc.get(4), smallArc.get(5), smallArc.get(6), smallArc.get(7));
        cs.closePath();
    }
    
    /**
     *  From https://hansmuller-flex.blogspot.com/2011/10/more-about-approximating-circular-arcs.html
     * 
     *  Cubic bezier approximation of a circular arc centered at the origin, 
     *  from (radians) a1 to a2, where a2-a1 &lt; pi/2.  The arc's radius is r.
     * 
     *  Returns a list with 4 points, where x1,y1 and x4,y4 are the arc's end points
     *  and x2,y2 and x3,y3 are the cubic bezier's control points.
     * 
     *  This algorithm is based on the approach described in:
     *  Aleksas Riškus, "Approximation of a Cubic Bezier Curve by Circular Arcs and Vice Versa," 
     *  Information Technology and Control, 35(4), 2006 pp. 371-378.
     */
    private static List<Float> createSmallArc(double r, double a1, double a2)
    {
        // Compute all four points for an arc that subtends the same total angle
        // but is centered on the X-axis
        double a = (a2 - a1) / 2;
        double x4 = r * Math.cos(a);
        double y4 = r * Math.sin(a);
        double x1 = x4;
        double y1 = -y4;
        double q1 = x1*x1 + y1*y1;
        
        double q2 = q1 + x1*x4 + y1*y4;
        double k2 = 4/3d * (Math.sqrt(2 * q1 * q2) - q2) / (x1 * y4 - y1 * x4);
        double x2 = x1 - k2 * y1;
        double y2 = y1 + k2 * x1;
        double x3 = x2; 
        double y3 = -y2;
        
        // Find the arc points' actual locations by computing x1,y1 and x4,y4 
        // and rotating the control points by a + a1
        
        double ar = a + a1;
        double cos_ar = Math.cos(ar);
        double sin_ar = Math.sin(ar);
        
        List<Float> list = new ArrayList<Float>();
        list.add((float) (r * Math.cos(a1)));
        list.add((float) (r * Math.sin(a1))); 
        list.add((float) (x2 * cos_ar - y2 * sin_ar)); 
        list.add((float) (x2 * sin_ar + y2 * cos_ar)); 
        list.add((float) (x3 * cos_ar - y3 * sin_ar)); 
        list.add((float) (x3 * sin_ar + y3 * cos_ar)); 
        list.add((float) (r * Math.cos(a2))); 
        list.add((float) (r * Math.sin(a2)));
        return list;
    }
}

如果您在切片之间出现白线并且不希望出现这种情况，请参阅。

Answer 2

如果您只想使用 PDFBox 将一些图表绘制成 PDF 而不想自己完成所有数学运算等，您可以使用我的 PDFBox Graphics2D adapter。这允许您使用任何基于 Graphics2D 的 java 库来绘制图表（例如 JFreeChart）。它将创建一个 XForm，然后您可以将其自由放置在 PDF 中。

如果您真的想自己做，您仍然可以使用 Java2D API 来帮助处理形状。

Arc2D.Float arc = new Arc2D.Float(x,y,w,h,start,extend, Arch2D.OPEN);
AffineTransform tf = new AffineTransform();
// You may need to setup tf to correctly position the drawing.
float[] coords = new float[6];
PathIterator pi = arc.getPathIterator(tf);
while (!pi.isDone()) {
    int segment = pi.currentSegment(coords);
    switch (segment) {
    case PathIterator.SEG_MOVETO:
        if (isFinite(coords, 2))
            contentStream.moveTo(coords[0], coords[1]);
        break;
    case PathIterator.SEG_LINETO:
        if (isFinite(coords, 2))
            contentStream.lineTo(coords[0], coords[1]);
        break;
    case PathIterator.SEG_QUADTO:
        if (isFinite(coords, 4))
            contentStream.curveTo1(coords[0], coords[1], coords[2], coors[3]);
            break;
    case PathIterator.SEG_CUBICTO:
        if (isFinite(coords, 6))
            contentStream.curveTo(coords[0], coords[1], coords[2], coords[3], coords[4], coords[5]);
        break;
    case PathIterator.SEG_CLOSE:
        contentStream.closePath();
        break;
    }
    pi.next();
}
contentStream.fill();

另见 my graphics adapter shape walking code。

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