如何使曲线连接两个对象可编辑？

Question

我参与了一个项目，我们正在做一个可视化编辑器（用Java编写）。现在，我正在尝试制作连接两个不同对象的曲线，我在一个扩展JPanel的类中绘制（这个类是我用来绘制的，在JFrame中，覆盖方法paintComponent）。我遇到了麻烦，因为我正在使用QuadCurve2D类来实现这一点，但是我无法使其成为可点击的（我使用的方法包含，但它不是每次都有效），让它可编辑（例如，设置一个在中间点使用square来修改它的曲率。当调用构造函数时，QuadCurve2D中间使用的点在曲线之外）或某些东西（方法，变量，迭代器等）可以告诉我哪些点在QuadCurve2D。

在寻找所有这些时间之后，我没有回答，所以我试着在这里发布它以找到解决方案。无论如何使用QuadCurve2D类，或者我必须尝试使用​​一些外部库吗？

Answer 1

首先对不起，回复很久。我现在正在发布你问题的完整答案。我正在对QuadCurve2D.Double类进行子类化，现在您可以使用开始，结束和中间点而不是控制点来定义曲线。我还创建了一个新方法来检查一个点是否在曲线上。交叉方法检查形状的凸包是否与提供的形状相交，因此在凹曲线的情况下，这是有效但不准确的。请注意，我检查点是否在曲线上的方法的实现在计算上相当昂贵并且不是100％准确，因为我使用指定的分辨率检查曲线长度（0是曲线的开头，1是结束因此，在提供的示例中，我使用0.01的分辨率进行检查，这意味着沿着曲线进行了100次检查。为此，请确保分辨率中提供的步骤是0.5（中间点）的分隔符，以便您可以选择它。如果没有意义就不注意它并不重要，你可以开箱即用我的例子。请注意，我还提供了一个复选框，用于在intersects方法和我自己的方法之间切换，以检查鼠标是否在曲线上。当使用我的新方法时，我还提供了一个滑块来指定分辨率，以便您可以看到各种值的效果。这是课程。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Point2D;

import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;

@SuppressWarnings("serial")
public class CurvePanel extends JPanel implements MouseListener,MouseMotionListener{

    Point2D startPoint = new Point2D.Double(50, 50);
    Point2D middlePoint = new Point2D.Double(100,80);
    Point2D endPoint = new Point2D.Double(200, 200);
    Point2D[] points = new Point2D[] {startPoint,middlePoint,endPoint};
    QuadCurveWithMiddlePoint curve;
    private Point2D movingPoint;
    private boolean dragIt = false;
    private boolean showControls = false;
    JCheckBox useNewMethod;
    JSlider resolution;

    public CurvePanel() {
        setPreferredSize(new Dimension(300,300));
        addMouseListener(this);
        addMouseMotionListener(this);
        curve = new QuadCurveWithMiddlePoint();
        useNewMethod = new JCheckBox("Use new \"contains\" method");
        resolution = new JSlider(JSlider.HORIZONTAL,1,10,1);
        useNewMethod.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                resolution.setEnabled(useNewMethod.isSelected());
            }
        });
        useNewMethod.setSelected(false);
        resolution.setEnabled(false);
        setCurve();
    }

    private void setCurve() {
        curve.setCurveWithMiddlePoint(startPoint, middlePoint, endPoint);
    }

    public static void main(String[] args) {
        JFrame f = new JFrame("Test");
        CurvePanel panel = new CurvePanel();
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(panel.useNewMethod,BorderLayout.NORTH);
        f.getContentPane().add(panel,BorderLayout.CENTER);
        f.getContentPane().add(panel.resolution,BorderLayout.SOUTH);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
    }

    @Override
    public void mouseClicked(MouseEvent e)  {}
    @Override
    public void mouseEntered(MouseEvent e) {}
    @Override
    public void mouseExited(MouseEvent e) {}
    @Override
    public void mousePressed(MouseEvent e) {
        for (Point2D point : points) {
            if (e.getPoint().distance(point) <= 2) {
                movingPoint = point;
                dragIt = true;
            }
        }
    }
    @Override
    public void mouseReleased(MouseEvent e) {
        dragIt = false;
    }
    @Override
    public void mouseDragged(MouseEvent e) {
        if (dragIt) {
            movingPoint.setLocation(e.getPoint());
            setCurve();
            repaint();
        }
    }
    @Override
    public void mouseMoved(MouseEvent e) {
        if (useNewMethod.isSelected())
            showControls = curve.pointOnCurve(e.getPoint(), 2, resolution.getValue()/100.0);
        else
            showControls = curve.intersects(e.getX()-2, e.getY()-2, 4, 4);
        repaint();
    }
    @Override
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setPaint(Color.white);
        g2.fillRect(0, 0, getWidth(), getHeight());
        g2.setPaint(Color.black);
        g2.draw(curve);
        if (showControls)
            for (Point2D point : points) {
                g2.setPaint(Color.black);
                g2.drawOval((int)point.getX()-2, (int)point.getY()-2, 4, 4);
                g2.setPaint(Color.red);
                g2.fillOval((int)point.getX()-2, (int)point.getY()-2, 4, 4);
            }
    }
}

还有：

import java.awt.geom.Point2D;
import java.awt.geom.QuadCurve2D.Double;

@SuppressWarnings("serial")
public class QuadCurveWithMiddlePoint extends Double {

    private Point2D middlePoint = new Point2D.Double();
    private final double L = 0.5;

    public QuadCurveWithMiddlePoint(double x1,double y1, double xm, double ym, double x2, double y2) {
        super(x1,y1,xm,ym,x2,y2);
        setMiddlePoint(xm, ym);
    }

    public QuadCurveWithMiddlePoint() {
        this(0,0,0,0,0,0);
    }

    public Point2D getMiddlePoint() {
        calculateMiddlePoint();
        return middlePoint;
    }

    public void setMiddlePoint(double middleX, double middleY) {
        setCurve(getP1(), getControlPointByMiddle(middleX, middleY), getP2());
        calculateMiddlePoint();
    }

    public void setMiddlePoint(Point2D middle) {
        setMiddlePoint(middle.getX(),middle.getY());
    }

    private Point2D getControlPointByMiddle(double middleX,double middleY) {
        double cpx = (middleX-(L*L-2*L+1)*x1-(L*L)*x2)/(-2*L*L+2*L);
        double cpy = (middleY-(L*L-2*L+1)*y1-(L*L)*y2)/(-2*L*L+2*L);
        return new Point2D.Double(cpx,cpy);
    }

    private Point2D calculatePoint(double position) {
        if (position<0 || position>1)
            return null;
        double middlex = (position*position-2*position+1)*x1+(-2*position*position+2*position)*ctrlx+(position*position)*x2;
        double middley = (position*position-2*position+1)*y1+(-2*position*position+2*position)*ctrly+(position*position)*y2;
        return new Point2D.Double(middlex,middley);
    }

    public void calculateMiddlePoint() {
        middlePoint.setLocation(calculatePoint(L));
    }

    public void setCurveWithMiddlePoint(double xx1,double yy1, double xxm, double yym, double xx2, double yy2) {
        setCurve(xx1, yy1, xxm, yym, xx2, yy2);
        setMiddlePoint(xxm,yym);
    }

    public void setCurveWithMiddlePoint(Point2D start, Point2D middle, Point2D end) {
        setCurveWithMiddlePoint(start.getX(),start.getY(),middle.getX(),middle.getY(),end.getX(),end.getY());
    }

    public boolean pointOnCurve(Point2D point, double accuracy, double step) {
        if (accuracy<=0)
            return false;
        if (step<=0 || step >1)
            return false;
        boolean oncurve = false;
        double current = 0;
        while (!oncurve && current <= 1) {
            if (calculatePoint(current).distance(point)<accuracy)
                oncurve = true;
            current += step;
        }
        return oncurve;
    }

}

如果你想知道我是如何上课的，可以搜索基本的线性代数，也可以搜索维基百科Bézier curves。