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我想绘制一个箭头在一个圆圈(如时钟指针),但我无法对齐箭头的其余部分。如何用java2d绘制箭头?
我做了“箭头”根据this answer,但我不能使它正确定位与线条画。
的箭头是越到线的左侧,在图像中如下:
这里我MCVE:
import java.awt.BasicStroke;
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.Polygon;
import java.awt.geom.AffineTransform;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
public class LineArrowTest extends JFrame {
private static final long serialVersionUID = 1L;
private JPanel contentPane;
private JPanel DrawPanel;
public static void main(String[] args) {
EventQueue.invokeLater(() -> {
new LineArrowTest().setVisible(true);
});
}
public LineArrowTest() {
initComponents();
pack();
}
private void initComponents() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setPreferredSize(new Dimension(400, 300));
this.contentPane = new JPanel(new BorderLayout(0, 0));
this.contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(this.contentPane);
this.DrawPanel = new JPanel() {
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
LineArrow line = new LineArrow(getWidth()/2, getHeight()/2, getWidth()/2, getHeight(),
Color.black, 3);
line.draw(g);
}
};
this.contentPane.add(this.DrawPanel, BorderLayout.CENTER);
}
class LineArrow {
int x;
int y;
int endX;
int endY;
Color color;
int thickness;
public LineArrow(int x, int y, int x2, int y2, Color color, int thickness) {
super();
this.x = x;
this.y = y;
this.endX = x2;
this.endY = y2;
this.color = color;
this.thickness = thickness;
}
public void draw(Graphics g) {
Graphics2D g2 = (Graphics2D) g.create();
g2.setColor(color);
g2.setStroke(new BasicStroke(thickness));
g2.drawLine(x, y, endX, endY);
;
drawArrowHead(g2);
g2.dispose();
}
private void drawArrowHead(Graphics2D g2) {
Polygon arrowHead = new Polygon();
AffineTransform tx = new AffineTransform();
arrowHead.addPoint(0, 5);
arrowHead.addPoint(-5, -5);
arrowHead.addPoint(5, -5);
tx.setToIdentity();
double angle = Math.atan2(endY - y, endX - x);
tx.translate(endX, endY);
tx.rotate(angle - Math.PI/2d);
g2.setTransform(tx);
g2.fill(arrowHead);
}
}
}
不想滥用你的善意,但它为什么会发生?如果我删除了'this.contentPane.setBorder(new EmptyBorder(5,5,5,5));'这个箭头就变成了正常。 – Articuno
边界正是问题所在。边框宽5像素。绘制组件时,边框是组件的一部分,因此坐标(0,0)将位于边框“外部”。在绘制线条时,Graphics2D的默认转换通过添加(5,5)(=边框的宽度)的平移来补偿此效果。但是当你设置你的转换时,你首先将它设置为标识,然后缺少这个额外的转换,导致错误对齐的边界宽度。 – cello
['Graphics2D']的Javadoc(https://docs.oracle.com/javase/8/docs/api/java/awt/Graphics2D.html):*创建Graphics2D对象时,GraphicsConfiguration指定默认的转换Graphics2D(组件或图像)的目标。此默认转换将用户空间坐标系映射到屏幕和打印机设备坐标,以便原点映射到设备目标区域的左上角,同时向右扩展X坐标并增加向下延伸的Y坐标* – Andreas