嗨我在java中有一些绘制矩形的代码,但是它只会向右拖动,即使我向左拖动也向右拖动,这里的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();
答案 0 :(得分:3)
请注意,Rectangle
(以及Graphics#fillRect
和Graphics#drawRect
)不会呈现负宽度/高度的矩形
你需要两件事......
你应该从mousePressed
事件......
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,并将其用于维度。
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();
}
}
}
答案 1 :(得分:0)
让我们做一些简单的代数。
selection.x - e.getX()
与
相同- (e.getX() - selection.x)
所以你的表达是这样说的:
Math.max(- (e.getX() - selection.x), e.getX() - selection.x)
由于正面版本总是会更大,所以它总会选择正面答案,因此你永远不会得到一个负宽度/高度的矩形。