如何在Java中绘制有向箭头线？ [英] How to draw a directed arrow line in Java?
问题描述
我想在Java中绘制一条有向箭头线。
I want to draw a directed arrow line through Java.
目前，我正在使用 java.awt.Line2D.Double 绘制一条线的类
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));
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。
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.
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。
The line I am drawing meets the border of a rectangle but no directed arrow is drawn. Only a simple line is drawn.
我有什么遗漏的吗？
推荐答案
如果折线处于特定角度，则在折线中的线段之间绘制斜角。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条，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）。
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 ).
要绘制一个简单的箭头，在你做的时候画一条线，然后用一条折线小提琴。看起来更好的箭头有弯曲的边和填充。
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.
你可能不想使用斜面作为箭头，因为斜面是平的;而是使用斜接选项：
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 ) );
}
}
}
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