我想在Java中绘制一条有向箭头线。
目前，我正在使用java.awt.Line2D.Double类画一条线
g2.setStroke(new BasicStroke(2.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_BEVEL)); // g2 is an instance of Graphics2D
g2.draw(new Line2D.Double(x1,y1,x2,y2));
但只显示该行，并且不显示有向箭头。 BasicStroke.Join_BEVEL用于绘制有向箭头。当两个线段相遇时应用它。
我绘制的线条符合矩形的边框，但没有绘制有向箭头。只绘制一条简单的线条。
有什么我想念的吗？
如果它们处于某个角度，则在折线中的段之间绘制斜角。如果您正在绘制一条恰好在某些其他具有某种颜色的像素附近绘制的线，则它没有任何影响 - 一旦绘制了矩形，Graphics对象就不知道矩形，它（实际上）只保留像素。 （或者更确切地说，图像或OS窗口保持像素）。
要画一个简单的箭头，在你做的时候画一条茎线，然后画一条vee的折线。看起来更好的箭头有弯曲的边和填充。
您可能不希望使用斜角作为箭头，因为斜面是平的;而是使用斜接选项：
import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
public class BevelArrows
{
public static void main ( String...args )
{
SwingUtilities.invokeLater ( new Runnable () {
BevelArrows arrows = new BevelArrows();
@Override
public void run () {
JFrame frame = new JFrame ( "Bevel Arrows" );
frame.add ( new JPanel() {
public void paintComponent ( Graphics g ) {
arrows.draw ( ( Graphics2D ) g, getWidth(), getHeight() );
}
}
, BorderLayout.CENTER );
frame.setSize ( 800, 400 );
frame.setDefaultCloseOperation ( JFrame.EXIT_ON_CLOSE );
frame.setVisible ( true );
}
} );
}
interface Arrow {
void draw ( Graphics2D g );
}
Arrow[] arrows = { new LineArrow(), new CurvedArrow() };
void draw ( Graphics2D g, int width, int height )
{
g.setRenderingHint ( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON );
g.setColor ( Color.WHITE );
g.fillRect ( 0, 0, width, height );
for ( Arrow arrow : arrows ) {
g.setColor ( Color.ORANGE );
g.fillRect ( 350, 20, 20, 280 );
g.setStroke ( new BasicStroke ( 20.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_BEVEL ) );
g.translate ( 0, 60 );
arrow.draw ( g );
g.setStroke ( new BasicStroke ( 20.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER ) );
g.translate ( 0, 100 );
arrow.draw ( g );
g.setStroke ( new BasicStroke ( 20.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_ROUND ) );
g.translate ( 0, 100 );
arrow.draw ( g );
g.translate ( 400, -260 );
}
}
static class LineArrow implements Arrow
{
public void draw ( Graphics2D g )
{
// where the control point for the intersection of the V needs calculating
// by projecting where the ends meet
float arrowRatio = 0.5f;
float arrowLength = 80.0f;
BasicStroke stroke = ( BasicStroke ) g.getStroke();
float endX = 350.0f;
float veeX;
switch ( stroke.getLineJoin() ) {
case BasicStroke.JOIN_BEVEL:
// IIRC, bevel varies system to system, this is approximate
veeX = endX - stroke.getLineWidth() * 0.25f;
break;
default:
case BasicStroke.JOIN_MITER:
veeX = endX - stroke.getLineWidth() * 0.5f / arrowRatio;
break;
case BasicStroke.JOIN_ROUND:
veeX = endX - stroke.getLineWidth() * 0.5f;
break;
}
// vee
Path2D.Float path = new Path2D.Float();
path.moveTo ( veeX - arrowLength, -arrowRatio*arrowLength );
path.lineTo ( veeX, 0.0f );
path.lineTo ( veeX - arrowLength, arrowRatio*arrowLength );
g.setColor ( Color.BLUE );
g.draw ( path );
// stem for exposition only
g.setColor ( Color.YELLOW );
g.draw ( new Line2D.Float ( 50.0f, 0.0f, veeX, 0.0f ) );
// in practice, move stem back a bit as rounding errors
// can make it poke through the sides of the Vee
g.setColor ( Color.RED );
g.draw ( new Line2D.Float ( 50.0f, 0.0f, veeX - stroke.getLineWidth() * 0.25f, 0.0f ) );
}
}
static class CurvedArrow implements Arrow
{
// to draw a nice curved arrow, fill a V shape rather than stroking it with lines
public void draw ( Graphics2D g )
{
// as we're filling rather than stroking, control point is at the apex,
float arrowRatio = 0.5f;
float arrowLength = 80.0f;
BasicStroke stroke = ( BasicStroke ) g.getStroke();
float endX = 350.0f;
float veeX = endX - stroke.getLineWidth() * 0.5f / arrowRatio;
// vee
Path2D.Float path = new Path2D.Float();
float waisting = 0.5f;
float waistX = endX - arrowLength * 0.5f;
float waistY = arrowRatio * arrowLength * 0.5f * waisting;
float arrowWidth = arrowRatio * arrowLength;
path.moveTo ( veeX - arrowLength, -arrowWidth );
path.quadTo ( waistX, -waistY, endX, 0.0f );
path.quadTo ( waistX, waistY, veeX - arrowLength, arrowWidth );
// end of arrow is pinched in
path.lineTo ( veeX - arrowLength * 0.75f, 0.0f );
path.lineTo ( veeX - arrowLength, -arrowWidth );
g.setColor ( Color.BLUE );
g.fill ( path );
// move stem back a bit
g.setColor ( Color.RED );
g.draw ( new Line2D.Float ( 50.0f, 0.0f, veeX - arrowLength * 0.5f, 0.0f ) );
}
}
}
尽管Pete的帖子非常全面，但我正在使用这种方法绘制一条非常简单的线，其末端有一个小三角形。
// create an AffineTransform
// and a triangle centered on (0,0) and pointing downward
// somewhere outside Swing's paint loop
AffineTransform tx = new AffineTransform();
Line2D.Double line = new Line2D.Double(0,0,100,100);
Polygon arrowHead = new Polygon();
arrowHead.addPoint( 0,5);
arrowHead.addPoint( -5, -5);
arrowHead.addPoint( 5,-5);
// [...]
private void drawArrowHead(Graphics2D g2d) {
tx.setToIdentity();
double angle = Math.atan2(line.y2-line.y1, line.x2-line.x1);
tx.translate(line.x2, line.y2);
tx.rotate((angle-Math.PI/2d));
Graphics2D g = (Graphics2D) g2d.create();
g.setTransform(tx);
g.fill(arrowHead);
g.dispose();
}
在过去，我已经编写了以下方法来创建一个箭头形状，然后我可以填充（（Graphics2D）g）.fill（shape）;
public static Shape createArrowShape(Point fromPt, Point toPt) {
Polygon arrowPolygon = new Polygon();
arrowPolygon.addPoint(-6,1);
arrowPolygon.addPoint(3,1);
arrowPolygon.addPoint(3,3);
arrowPolygon.addPoint(6,0);
arrowPolygon.addPoint(3,-3);
arrowPolygon.addPoint(3,-1);
arrowPolygon.addPoint(-6,-1);
Point midPoint = midpoint(fromPt, toPt);
double rotate = Math.atan2(toPt.y - fromPt.y, toPt.x - fromPt.x);
AffineTransform transform = new AffineTransform();
transform.translate(midPoint.x, midPoint.y);
double ptDistance = fromPt.distance(toPt);
double scale = ptDistance / 12.0; // 12 because it's the length of the arrow polygon.
transform.scale(scale, scale);
transform.rotate(rotate);
return transform.createTransformedShape(arrowPolygon);
}
private static Point midpoint(Point p1, Point p2) {
return new Point((int)((p1.x + p2.x)/2.0),
(int)((p1.y + p2.y)/2.0));
}
这是我的方法，绝对数学：
/**
* Draw an arrow line between two points.
* @param g the graphics component.
* @param x1 x-position of first point.
* @param y1 y-position of first point.
* @param x2 x-position of second point.
* @param y2 y-position of second point.
* @param d the width of the arrow.
* @param h the height of the arrow.
*/
private void drawArrowLine(Graphics g, int x1, int y1, int x2, int y2, int d, int h) {
int dx = x2 - x1, dy = y2 - y1;
double D = Math.sqrt(dx*dx + dy*dy);
double xm = D - d, xn = xm, ym = h, yn = -h, x;
double sin = dy / D, cos = dx / D;
x = xm*cos - ym*sin + x1;
ym = xm*sin + ym*cos + y1;
xm = x;
x = xn*cos - yn*sin + x1;
yn = xn*sin + yn*cos + y1;
xn = x;
int[] xpoints = {x2, (int) xm, (int) xn};
int[] ypoints = {y2, (int) ym, (int) yn};
g.drawLine(x1, y1, x2, y2);
g.fillPolygon(xpoints, ypoints, 3);
}
如果你想要快速方式的非程序化箭头（即用于文本目的），你可以使用<html>代码将箭头作为文本，只需将你的HTML代码放在.setText()方法中作为组件。我有java 1.8u202它工作正常。
myLabel.setText("<html><body>←</body></html>");
这段代码
←用于左箭头
来自This Website的其他箭头方向HTML代码