4

我正在使用AreasJava。

我的测试程序随机绘制三个三角形并将它们组合成一个或多个多边形。将Areas它们.add()结合在一起后,我用它PathIterator来追踪边缘。

然而,有时,这些Area对象不会按应有的方式组合......正如您在我发布的最后一张图片中看到的那样,将绘制额外的边缘。

认为这个问题是由 JavaArea类中的舍入不准确引起的(当我调试测试程序时,Area显示了使用之前的差距PathIterator),但我认为 Java 没有提供任何其他组合形状的方法。

有什么解决办法吗?

示例代码和图像:

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();
    }
}

成功案例:

成功

一个失败的案例:

失败

4

3 回答 3

4

这里:

    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));
    }       

您实际上在第一个循环中添加了 1 个三角形 在第二个循环中添加了 2 个三角形 在第三个循环中添加了 3 个三角形

这就是您的不准确之处的来源。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();
    }    

请注意每个循环后的路径重置。

编辑:更多地解释不准确来自这里的三个路径,您尝试结合。这使得可能出现错误的地方很明显。

第一条路径

第二条路径

第三条路径

于 2012-03-04T17:17:02.643 回答
2

我重新考虑了您的示例以使测试更容易,并添加了两个答案的功能。恢复triangle.reset()似乎消除了我的工件。此外,

  • 在事件分派线程上构建 GUI 。

  • 对于渲染,扩展一个JComponent,例如JPanel,并覆盖paintComponent()

  • 缺少具有首选大小的子组件 override 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);
            }
        });
    }
}
于 2012-03-04T23:21:21.627 回答
1

我玩弄了这个,并找到了一种摆脱这些的hacky方法。我不是 100% 确定这在所有情况下都有效,但它可能。

读完Area.transform的 JavaDoc 提到

使用指定的 AffineTransform 变换此区域的几何图形。几何图形在原地变换,这将永久更改此对象定义的封闭区域。

我有一种预感,并增加了通过按住一个键来旋转区域的可能性。随着区域的旋转,“向内”的边缘开始慢慢消失,直到只剩下轮廓。我怀疑“向内”边缘实际上是两个非常接近的边缘(因此它们看起来像单个边缘),并且旋转区域会导致非常小的舍入误差,因此旋转类型将它们“融化”在一起。

然后我添加了一个代码,在按键上以非常小的步长将区域旋转一整圈,看起来工件消失了:

在此处输入图像描述

左边的图像是由 10 个不同的随机三角形构建的区域(我增加了三角形的数量以更频繁地获得“失败”区域),右边的图像是相同的区域,在非常旋转 360 度后小增量(10000 步)。

这是用于以小步长旋转区域的一段代码(对于大多数情况,小于 10000 步的数量可能会很好):

        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更小或更大,具体取决于场景。YMMV。

于 2012-03-04T10:56:44.603 回答