java中如何实现画线段,如何在Java中绘制有向箭头线？

绝地灬酷狼 2023-01-24 02:29 18阅读 0赞

![Image 1][]

I want to draw a directed arrow line through Java.

At present, I am using java.awt.Line2D.Double class to draw a line

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));

But only the line appears and no directed arrow appears. BasicStroke.Join\_BEVEL is used to draw a directed arrow. It is applied when two line segments meet.

The line I am drawing meets the border of a rectangle but no directed arrow is drawn. Only a simple line is drawn.

Is there anything I am missing?

解决方案

The bevel is drawn between segments in a polyline if they are at certain angles. It has no bearing if you are drawing a line which happens to be drawn near some other pixels which are of a certain colour - once you've drawn the rectangle, the Graphics object doesn't know about the rectangle, it (in effect) only holds the pixels. ( or rather the image or OS window holds the pixels ).

To draw a simple arrow, draw a line for the stalk as you're doing, then a polyline for the vee. Nicer looking nicer arrows have curved sides and are filled.

You probably don't want to use bevel for the arrow head, as bevels are a flat; instead use the mitre option:

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 ) );

[Image 1]:

java中如何实现画线段,如何在Java中绘制有向箭头线？

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