java以一种方式绘制矩形而不是同时使用两种方式

Question

嗨，我在java中有一些代码可以绘制一个矩形，但是它只会向右拖动，即使我向左拖动它也会向右拖动，这是代码，我有什么帮助吗？

  public void mouseDragged(MouseEvent e) {
                    Point p = e.getPoint();
                    int width = Math.max(selection.x - e.getX(), e.getX() - selection.x);
                    int height = Math.max(selection.y - e.getY(), e.getY() - selection.y);
                    selection.setSize(width, height);
                    repaint();

Answer 1

请记住，矩形(以及Graphics#fillRect和Graphics#drawRect)不会渲染具有负宽度/高度的矩形

你需要两件事......

1. 当前鼠标点(或您的情况下的拖动点)
2. 第一次按下鼠标的点( anchor 或原点)

您应该从 mousePressed 事件中获取 anchor ...

public void mousePressed(MouseEvent e) {
    clickPoint = new Point(e.getPoint());
}

然后，您需要确定哪个点最小并将其用作起点，哪个点最大并将其用作尺寸。

public void mouseDragged(MouseEvent e) {
    int minX = Math.min(e.getX(), clickPoint.x);
    int minY = Math.min(e.getY(), clickPoint.y);
    int maxX = Math.max(e.getX(), clickPoint.x);
    int maxY = Math.max(e.getY(), clickPoint.y);

    selection.x = minX;
    selection.y = minY;
    selection.width = maxX - minX;
    selection.height = maxY - minY;
    repaint();
}

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.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class SelectionExample {

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

    public SelectionExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Rectangle selection = new Rectangle();
        private Point clickPoint;

        public TestPane() {
            MouseAdapter ma = new MouseAdapter() {

                @Override
                public void mouseDragged(MouseEvent e) {
                    int minX = Math.min(e.getX(), clickPoint.x);
                    int minY = Math.min(e.getY(), clickPoint.y);
                    int maxX = Math.max(e.getX(), clickPoint.x);
                    int maxY = Math.max(e.getY(), clickPoint.y);

                    selection.x = minX;
                    selection.y = minY;
                    selection.width = maxX - minX;
                    selection.height = maxY - minY;
                    repaint();
                }

                @Override
                public void mousePressed(MouseEvent e) {
                    clickPoint = new Point(e.getPoint());
                }

            };

            addMouseListener(ma);
            addMouseMotionListener(ma);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (selection.width > 0 && selection.height > 0) {
                g2d.setColor(new Color(0, 0, 255, 64));
                g2d.fill(selection);
                g2d.setColor(Color.BLUE);
                g2d.draw(selection);
            }
            g2d.dispose();
        }
    }

}