Question

我在Java中使用Areas。

我的测试程序绘制三个随机三角形并将它们组合成一个或多个多边形。在Areas .add()编辑后，我使用PathIterator来跟踪边缘。

但是，有时Area个对象不会按照它们的要求组合......正如您在上次发布的图像中所看到的那样，将绘制额外的边缘。

我认为问题是由Java Area类中的舍入不准确引起的（当我调试测试程序时，Area显示PathIterator之前的空白使用），但我不认为Java提供任何其他方式来组合形状。

任何解决方案？

示例代码和图片：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Area;
import java.awt.geom.Line2D;
import java.awt.geom.Path2D;
import java.awt.geom.PathIterator;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JFrame;

public class AreaTest extends JFrame{
    private static final long serialVersionUID = -2221432546854106311L;


    Area area = new Area();
    ArrayList<Line2D.Double> areaSegments = new ArrayList<Line2D.Double>();

    AreaTest() {
        Path2D.Double triangle = new Path2D.Double();
        Random random = new Random();

        // Draw three random triangles
        for (int i = 0; i < 3; i++) {
            triangle.moveTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
            triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
            triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
            triangle.closePath();
            area.add(new Area(triangle));
        }       

        // Note: we're storing double[] and not Point2D.Double
        ArrayList<double[]> areaPoints = new ArrayList<double[]>();
        double[] coords = new double[6];

        for (PathIterator pi = area.getPathIterator(null); !pi.isDone(); pi.next()) {

            // Because the Area is composed of straight lines
            int type = pi.currentSegment(coords);
            // We record a double array of {segment type, x coord, y coord}
            double[] pathIteratorCoords = {type, coords[0], coords[1]};
            areaPoints.add(pathIteratorCoords);
        }

        double[] start = new double[3]; // To record where each polygon starts
        for (int i = 0; i < areaPoints.size(); i++) {
            // If we're not on the last point, return a line from this point to the next
            double[] currentElement = areaPoints.get(i);

            // We need a default value in case we've reached the end of the ArrayList
            double[] nextElement = {-1, -1, -1};
            if (i < areaPoints.size() - 1) {
                nextElement = areaPoints.get(i + 1);
            }

            // Make the lines
            if (currentElement[0] == PathIterator.SEG_MOVETO) {
                start = currentElement; // Record where the polygon started to close it later
            } 

            if (nextElement[0] == PathIterator.SEG_LINETO) {
                areaSegments.add(
                        new Line2D.Double(
                            currentElement[1], currentElement[2],
                            nextElement[1], nextElement[2]
                        )
                    );
            } else if (nextElement[0] == PathIterator.SEG_CLOSE) {
                areaSegments.add(
                        new Line2D.Double(
                            currentElement[1], currentElement[2],
                            start[1], start[2]
                        )
                    );
            }
        }

        setSize(new Dimension(500, 500));
        setLocationRelativeTo(null); // To center the JFrame on screen
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setResizable(false);
        setVisible(true);
    }

    public void paint(Graphics g) {
        // Fill the area
        Graphics2D g2d = (Graphics2D) g;
        g.setColor(Color.lightGray);
        g2d.fill(area);

        // Draw the border line by line
        g.setColor(Color.black);
        for (Line2D.Double line : areaSegments) {
            g2d.draw(line);
        }
    }

    public static void main(String[] args) {
        new AreaTest();
    }
}

一个成功案例：

success

失败案例：

failure

Answer 1

下面：

    for (int i = 0; i < 3; i++) {
        triangle.moveTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.closePath();
        area.add(new Area(triangle));
    }

事实上，你正在加入第一个循环中有一个三角形第二个循环中有2个三角形第三个循环中有3个三角形

这是您的不准确之处。试试这个，看看你的问题是否仍然存在。

    for (int i = 0; i < 3; i++) {
        triangle.moveTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.lineTo(random.nextInt(400) + 50, random.nextInt(400) + 50);
        triangle.closePath();
        area.add(new Area(triangle));
        triangle.reset();
    }

注意每次循环后路径重置。

编辑：要解释更多来自这里的不准确之处，您尝试合并的三条路径。这显然可能出现错误。

First path

Second path

Third path

Answer 2

我重新考虑了你的例子，使测试更容易，添加了两个答案的功能。恢复triangle.reset()似乎消除了我的艺术品。另外，

在event dispatch thread。
要进行渲染，请扩展JComponent，例如JPanel，并覆盖paintComponent()。
缺少具有首选尺寸的子组件，请覆盖getPreferredSize()。
使用RenderingHints。

SSCCE：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.geom.AffineTransform;
import java.awt.geom.Area;
import java.awt.geom.Line2D;
import java.awt.geom.Path2D;
import java.awt.geom.PathIterator;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.SpinnerNumberModel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

/** @see http://stackoverflow.com/q/9526835/230513 */
public class AreaTest extends JPanel {

    private static final int SIZE = 500;
    private static final int INSET = SIZE / 10;
    private static final int BOUND = SIZE - 2 * INSET;
    private static final int N = 5;
    private static final AffineTransform I = new AffineTransform();
    private static final double FLATNESS = 1;
    private static final Random random = new Random();
    private Area area = new Area();
    private List<Line2D.Double> areaSegments = new ArrayList<Line2D.Double>();
    private int count = N;

    AreaTest() {
        setLayout(new BorderLayout());
        create();
        add(new JPanel() {

            @Override
            public void paintComponent(Graphics g) {
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(
                    RenderingHints.KEY_ANTIALIASING,
                    RenderingHints.VALUE_ANTIALIAS_ON);
                g.setColor(Color.lightGray);
                g2d.fill(area);
                g.setColor(Color.black);
                for (Line2D.Double line : areaSegments) {
                    g2d.draw(line);
                }
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(SIZE, SIZE);
            }
        });

        JPanel control = new JPanel();
        control.add(new JButton(new AbstractAction("Update") {

            @Override
            public void actionPerformed(ActionEvent e) {
                create();
                repaint();
            }
        }));
        JSpinner countSpinner = new JSpinner();
        countSpinner.setModel(new SpinnerNumberModel(N, 3, 42, 1));
        countSpinner.addChangeListener(new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                JSpinner s = (JSpinner) e.getSource();
                count = ((Integer) s.getValue()).intValue();
            }
        });
        control.add(countSpinner);
        add(control, BorderLayout.SOUTH);
    }

    private int randomPoint() {
        return random.nextInt(BOUND) + INSET;
    }

    private void create() {
        area.reset();
        areaSegments.clear();
        Path2D.Double triangle = new Path2D.Double();

        // Draw three random triangles
        for (int i = 0; i < count; i++) {
            triangle.moveTo(randomPoint(), randomPoint());
            triangle.lineTo(randomPoint(), randomPoint());
            triangle.lineTo(randomPoint(), randomPoint());
            triangle.closePath();
            area.add(new Area(triangle));
            triangle.reset();
        }

        // Note: we're storing double[] and not Point2D.Double
        List<double[]> areaPoints = new ArrayList<double[]>();
        double[] coords = new double[6];

        for (PathIterator pi = area.getPathIterator(I, FLATNESS);
            !pi.isDone(); pi.next()) {

            // Because the Area is composed of straight lines
            int type = pi.currentSegment(coords);
            // We record a double array of {segment type, x coord, y coord}
            double[] pathIteratorCoords = {type, coords[0], coords[1]};
            areaPoints.add(pathIteratorCoords);
        }

        // To record where each polygon starts
        double[] start = new double[3];
        for (int i = 0; i < areaPoints.size(); i++) {
            // If we're not on the last point, return a line from this point to the next
            double[] currentElement = areaPoints.get(i);

            // We need a default value in case we've reached the end of the List
            double[] nextElement = {-1, -1, -1};
            if (i < areaPoints.size() - 1) {
                nextElement = areaPoints.get(i + 1);
            }

            // Make the lines
            if (currentElement[0] == PathIterator.SEG_MOVETO) {
                // Record where the polygon started to close it later
                start = currentElement;
            }

            if (nextElement[0] == PathIterator.SEG_LINETO) {
                areaSegments.add(
                    new Line2D.Double(
                    currentElement[1], currentElement[2],
                    nextElement[1], nextElement[2]));
            } else if (nextElement[0] == PathIterator.SEG_CLOSE) {
                areaSegments.add(
                    new Line2D.Double(
                    currentElement[1], currentElement[2],
                    start[1], start[2]));
            }
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame f = new JFrame();
                f.add(new AreaTest());
                f.pack();
                f.setLocationRelativeTo(null);
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.setResizable(false);
                f.setVisible(true);
            }
        });
    }
}

Answer 3

我玩弄了这个，找到了一种摆脱这些的hacky方法。我不是百分百肯定这会在所有情况下都有效，但可能会这样。

在阅读Area.transform的JavaDoc提及

之后

使用指定的方法转换此Area的几何的AffineTransform。 将几何体转换到位，即永久更改此对象定义的封闭区域。

我有一种预感，并且通过按住一个键来增加旋转区域的可能性。当区域旋转时，“向内”边缘开始慢慢消失，直到只剩下轮廓。我怀疑“向内”边缘实际上是彼此非常接近的两条边（因此它们看起来像一条边），并且旋转区域会导致非常小的舍入不准确，因此旋转类型将它们“融合”在一起。 / p>

然后我添加了一个代码，用于在非常小的步骤中旋转区域，在按键上旋转一整圈，看起来这些文物消失了：

enter image description here

左边的图像是由10个不同的随机三角形构成的区域（我增加三角形的数量以更频繁地获得“失败”区域），右边的图像是完全旋转360度后的相同区域以非常小的增量（10000步）的度数。

这是用于以小步长旋转区域的代码段（对于大多数情况，小于10000步的量可能会很好）：

        final int STEPS = 10000; //Number of steps in a full 360 degree rotation
        double theta = (2*Math.PI) / STEPS; //Single step "size" in radians

        Rectangle bounds = area.getBounds();    //Getting the bounds to find the center of the Area
        AffineTransform trans = AffineTransform.getRotateInstance(theta, bounds.getCenterX(), bounds.getCenterY()); //Transformation matrix for theta radians around the center

        //Rotate a full 360 degrees in small steps
        for(int i = 0; i < STEPS; i++)
        {
            area.transform(trans);
        }

正如我之前所说，我不确定这是否适用于所有情况，并且所需的步骤数量可能会小得多或更大，具体取决于方案。 YMMV。

在Java中组合区域时舍入不准确？

3 个答案: