java - MouseEvent getX 和 getY 相对于实际坐标的偏移

Question

我正在编写一个基本的绘画程序，但我在 Rectangle 方面遇到了麻烦。和Ellipse工具。如果单击并拖动，您应该能够根据 startpoint 绘制尺寸的形状。和endpoint (都使用 getX() 和 getY() )，问题是这两个形状得到 startpoint对，但是endpoint在 x 和 y 坐标上都有偏移。

下面的代码与我在线条工具中使用的代码(工作正常)几乎相同，除了交换 Line2D与 Rectangle2D和Ellipse2D分别。

package tools;

import gui.DrawingPanel;

import java.awt.event.ActionEvent;

import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Rectangle2D;

import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ImageIcon;


/**
 * Creates the Rectangle Action.
 *@version 1
 */
public class RectangleAction extends AbstractAction {

    private final DrawingPanel myPanel;

    private Rectangle2D.Double myRectangle;
    private double Start_X;
    private double Start_Y;

    /**
     * Constructor for Rectangle Action.
     */
    public RectangleAction(final DrawingPanel thePanel) {
        super("Rectangle", getImageIcon()); 

        myPanel = thePanel;
        putValue(Action.MNEMONIC_KEY, KeyEvent.VK_R);
        putValue(Action.SELECTED_KEY, true);
    }

    @Override
    public void actionPerformed(final ActionEvent theEvent) {

        myPanel.addMouseListener(new MyMouseListener());
        myPanel.addMouseMotionListener(new MyMouseListener());

    }

    /**
     * gets the image icon of the action.
     * @return the image icon.
     */
    public static ImageIcon getImageIcon() {
        return new ImageIcon("./images/rectangle.gif");
    }    


    /**
     * Listens for mouse clicks, to draw on our panel.
     */
    private class MyMouseListener extends MouseAdapter {


        private double myX2;
        private double myY2;               


        /**
         * Handles a click event.
         * 
         * @param theEvent The event.
         */
        @Override
        public void mousePressed(final MouseEvent theEvent) {


            Start_X = (double) theEvent.getX();
            Start_Y = (double) theEvent.getY();
        }

        /**
         * Handles the release event.
         * 
         * @param theEvent The event.
         */
        @Override
        public void mouseReleased(final MouseEvent theEvent) {

            myX2 = (double) theEvent.getX();
            myY2 = (double) theEvent.getY();

            myRectangle = new Rectangle2D.Double(Start_X, Start_Y, myX2, myY2);

            myPanel.setShape(myRectangle);
            myPanel.repaint();           

        }

        /**
         * Handles a click event.
         * 
         * @param theEvent The event.
         */
        @Override
        public void mouseDragged(final MouseEvent theEvent) {

            myX2 = (double) theEvent.getX();
            myY2 = (double) theEvent.getY();

            myRectangle = new Rectangle2D.Double(Start_X, Start_Y, myX2, myY2);                                                                                          

            myPanel.setShape(myRectangle);
            myPanel.repaint();           

        }

    }

}

我应该注意，我确实查看了 this similar question但它并没有给我我正在寻找的答案；还有DrawingPanel只是一个 JPanel使用 Paint 组件来绘制形状，仅此而已。

Answer 1

myRectangle = new Rectangle2D.Double(Start_X, Start_Y, myX2, myY2);

参数是(x，y，宽度，高度)，您试图指定两个点。

您的绘画逻辑假设您始终将鼠标从上/左拖动到下/右。当您根据两点计算宽度/高度时，鼠标总是有可能向上和向左拖动，这会导致负值。

这是我用来正确计算矩形边界的代码:

int x = Math.min(startPoint.x, e.getX());
int y = Math.min(startPoint.y, e.getY());
int width = Math.abs(startPoint.x - e.getX());
int height = Math.abs(startPoint.y - e.getY());

您不需要创建两个监听器，只需共享同一个监听器即可:

//myPanel.addMouseListener(new MyMouseListener());
//myPanel.addMouseMotionListener(new MyMouseListener());
MouseAdapter myMouseAdapter = new MyMouseListener();
myPanel.addMouseListener( myMouseAdapter );
myPanel.addMouseMotionListener( myMouseAdapter);

此外，每次单击按钮时都会将适配器添加到面板。因此，如果您依次单击直线工具、椭圆工具和矩形工具，您将在面板中添加 3 个监听器。我建议您在为当前工具添加监听器之前，应从面板中删除所有监听器。