addMouseMotionListener坐标错误的问题 [英] Issue with addMouseMotionListener getting wrong coordinates

问题描述

我借用了下面的课程，为项目制作了选择区域工具.但是当内容未在左上角对齐时我尝试进行选择时会遇到问题，它会获得与ScrollPane相关的鼠标坐标，但会覆盖图像-请参阅此SS以获取更好的理解:

I borrowed the class below to make a selection area tool for a project. But it has a issue when I try to make a selection when the content is not aligned at top-left, it get my mouse coordinates related to the ScrollPane, but draws over the image - See this SS for better understanding:

场景:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.event.*;
import java.awt.image.*;

import javax.swing.*;

/** Getting a Rectangle of interest on the screen.
Requires the MotivatedEndUser API - sold separately. */
public class ScreenCaptureRectangle {

    Rectangle captureRect;

    ScreenCaptureRectangle(final BufferedImage screen) {
        final BufferedImage screenCopy = new BufferedImage(screen.getWidth(), screen.getHeight(), screen.getType());
        final JLabel screenLabel = new JLabel(new ImageIcon(screenCopy));
        JScrollPane screenScroll = new JScrollPane(screenLabel);

        screenScroll.setPreferredSize(new Dimension((int)(screen.getWidth()*2), (int)(screen.getHeight()*2)));

        JPanel panel = new JPanel(new BorderLayout());
        panel.add(screenScroll, BorderLayout.CENTER);

        final JLabel selectionLabel = new JLabel("Drag a rectangle in the screen shot!");
        panel.add(selectionLabel, BorderLayout.SOUTH);

        repaint(screen, screenCopy);
        screenLabel.repaint();

        screenLabel.addMouseMotionListener(new MouseMotionAdapter() {

            Point start = new Point();

            @Override
            public void mouseMoved(MouseEvent me) {
                start = me.getPoint();
                repaint(screen, screenCopy);
                selectionLabel.setText("Start Point: " + start);
                screenLabel.repaint();
            }

            @Override
            public void mouseDragged(MouseEvent me) {
                Point end = me.getPoint();
                captureRect = new Rectangle(start, new Dimension(end.x-start.x, end.y-start.y));
                repaint(screen, screenCopy);
                screenLabel.repaint();
                selectionLabel.setText("Rectangle: " + captureRect);
            }
        });

        JOptionPane.showMessageDialog(null, panel);

        System.out.println("Rectangle of interest: " + captureRect);
    }

    public void repaint(BufferedImage orig, BufferedImage copy) {
        Graphics2D g = copy.createGraphics();
        g.drawImage(orig,0,0, null);
        if (captureRect!=null) {
            g.setColor(Color.RED);
            g.draw(captureRect);
            g.setColor(new Color(255,255,255,150));
            g.fill(captureRect);
        }
        g.dispose();
    }

    public static void main(String[] args) throws Exception {
        Robot robot = new Robot();
        final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

        final BufferedImage screen = robot.createScreenCapture(new Rectangle(300,0,300,300));

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new ScreenCaptureRectangle(screen);
            }
        });
    }
}

推荐答案

我认为您遇到了问题，因为您试图将图像居中放置在面板中.

I think you have problems because you are attempting to center the image in the panel.

最简单的解决方案是确保从面板的顶部/左侧绘制图像:

The easiest solution is to make sure the image is painted from the top/left of the panel:

    final JLabel screenLabel = new JLabel(new ImageIcon(screenCopy));
    screenLabel.setHorizontalAlignment(JLabel.LEFT);
    screenLabel.setVerticalAlignment(JLabel.TOP);

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