Cómo dibujar un rectángulo en un applet de Java utilizando el evento de arrastre del ratón y hacer que se quede

Question

Tengo mi programa que puede dibujar rectángulos. Tengo dos problemas que no puede resolver. Después de que dibujar el rectángulo no permanecerá. El único código que tengo que borra el lienzo en menos de pintura, volver a pintar sólo se le llama el arrastre del ratón. ¿Por qué cuando la liberación del ratón o mover el ratón hace mi lienzo clara. La segunda cosa que no es tanto un problema, pero algo que no puedo entender, cuando la altura o anchura de mi rectángulo es negativo, el rectángulo se llena en negro.

package pracpapp2;


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class MouseTracker4July extends JFrame
   implements MouseListener, MouseMotionListener {


  private static final long serialVersionUID = 1L;
  private JLabel mousePosition;
  int x, y;
  int x1, x2, y1, y2;
  int w, h;
  private JLabel recStart;
  private JLabel recStop;
  private JLabel cords;
   // set up GUI and register mouse event handlers
   public MouseTracker4July()
   {
      super( "Rectangle Drawer" );

      mousePosition = new JLabel();
      mousePosition.setHorizontalAlignment(SwingConstants.CENTER);
      getContentPane().add( mousePosition, BorderLayout.CENTER );


      JLabel text1 = new JLabel();
      text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
      getContentPane().add( text1, BorderLayout.SOUTH );

      recStart = new JLabel();
      getContentPane().add(recStart, BorderLayout.WEST);

      recStop = new JLabel();
      getContentPane().add(recStop, BorderLayout.EAST);

      cords = new JLabel();
      getContentPane().add(cords, BorderLayout.NORTH);


      addMouseListener( this );        // listens for own mouse and
      addMouseMotionListener( this );  // mouse-motion events

      setSize( 800, 600 );
      setVisible( true );
   }

   // MouseListener event handlers
   // handle event when mouse released immediately after press
   public void mouseClicked( MouseEvent event )
   {
      mousePosition.setText( "Clicked at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   // handle event when mouse pressed
   public void mousePressed( MouseEvent event )
   {

      mousePosition.setText( "Pressed at [" +(x1 = event.getX()) +
         ", " + (y1 = event.getY()) + "]" );

      recStart.setText( "Start:  [" + x1 +
         ", " + y1 + "]" );
   }

   // handle event when mouse released after dragging
   public void mouseReleased( MouseEvent event )
   {
     mousePosition.setText( "Released at [" +(x2 = event.getX()) +
         ", " + (y2 = event.getY()) + "]" );

     recStop.setText( "End:  [" + x2 +
         ", " + y2 + "]" );

   }

   // handle event when mouse enters area
   public void mouseEntered( MouseEvent event )
   {
      mousePosition.setText( "Mouse entered at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   // handle event when mouse exits area
   public void mouseExited( MouseEvent event )
   {
      mousePosition.setText( "Mouse outside window" );
   }

   // MouseMotionListener event handlers
   // handle event when user drags mouse with button pressed
   public void mouseDragged( MouseEvent event )
   {
      mousePosition.setText( "Dragged at [" + (x = event.getX()) + 
         ", " + (y = event.getY()) + "]" );
      // call repaint which calls paint
      repaint();

   }

   // handle event when user moves mouse
   public void mouseMoved( MouseEvent event )
   {
      mousePosition.setText( "Moved at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   public void paint(Graphics g)
   {
      super.paint(g); // clear the frame surface
      g.drawString("Start Rec Here", x1, y1);
      g.drawString("End Rec Here", x, y);

      w = x1 - x;
      h = y1 - y;
      w = w * -1;
      h = h * -1;

      g.drawRect(x1, y1, w, h);

      cords.setText( "w = " + w + ", h = " + h);
   }

   public static void main( String args[] )
   { 
      MouseTracker4July application = new MouseTracker4July();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }

} // end class MouseTracker

Answer 1

Ok, después de volver a leer su pregunta, parece que podría importar menos tener múltiples rectángulos:)

Aquí es una solución con sólo uno a la vez (que está cerca de lo que tenía que empezar):

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;

public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {

    private static final long serialVersionUID = 1L;
    private final JLabel mousePosition;
    int x1, x2, y1, y2;
    int x, y, w, h;
    private final JLabel recStart;
    private final JLabel recStop;
    private final JLabel cords; // set up GUI and register mouse event handlers
    boolean isNewRect = true;

    public MouseTracker4July() {
        super( "Rectangle Drawer" );

        this.mousePosition = new JLabel();
        this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
        getContentPane().add( this.mousePosition, BorderLayout.CENTER );

        JLabel text1 = new JLabel();
        text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
        getContentPane().add( text1, BorderLayout.SOUTH );

        this.recStart = new JLabel();
        getContentPane().add( this.recStart, BorderLayout.WEST );

        this.recStop = new JLabel();
        getContentPane().add( this.recStop, BorderLayout.EAST );

        this.cords = new JLabel();
        getContentPane().add( this.cords, BorderLayout.NORTH );

        addMouseListener( this ); // listens for own mouse and
        addMouseMotionListener( this ); // mouse-motion events

        setSize( 800, 600 );
        setVisible( true );

    }

// MouseListener event handlers // handle event when mouse released immediately after press 
    public void mouseClicked( final MouseEvent event ) {
        this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );

        repaint();
    }

// handle event when mouse pressed 
    public void mousePressed( final MouseEvent event ) {

        this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );

        this.recStart.setText( "Start:  [" + this.x1 + ", " + this.y1 + "]" );

        this.isNewRect = true;

        repaint();
    }

// handle event when mouse released after dragging 
    public void mouseReleased( final MouseEvent event ) {
        this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );

        this.recStop.setText( "End:  [" + this.x2 + ", " + this.y2 + "]" );

        repaint();
    }

// handle event when mouse enters area 
    public void mouseEntered( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

// handle event when mouse exits area 
    public void mouseExited( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse outside window" );
        repaint();
    }

// MouseMotionListener event handlers // handle event when user drags mouse with button pressed 
    public void mouseDragged( final MouseEvent event ) {
        this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();

        this.isNewRect = false;

        repaint();
    }

// handle event when user moves mouse 
    public void mouseMoved( final MouseEvent event ) {
        this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

    @Override
    public void paint( final Graphics g ) {
        super.paint( g ); // clear the frame surface 
        g.drawString( "Start Rec Here", this.x1, this.y1 );
        g.drawString( "End Rec Here", this.x2, this.y2 );

        int width = this.x1 - this.x2;
        int height = this.y1 - this.y2;

        this.w = Math.abs( width );
        this.h = Math.abs( height );
        this.x = width < 0 ? this.x1
            : this.x2;
        this.y = height < 0 ? this.y1
            : this.y2;

        if ( !this.isNewRect ) {
            g.drawRect( this.x, this.y, this.w, this.h );
        }

        this.cords.setText( "w = " + this.w + ", h = " + this.h );

    }

    public static void main( final String args[] ) {
        MouseTracker4July application = new MouseTracker4July();
        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    }

} // end class MouseTracker

Answer 2

Es necesario para almacenar los elementos dibujados en alguna estructura de datos y asegurarse de que cada elemento de la estructura se pinta a la lona en el repintado.

Además, es necesario añadir repinte a cada uno de sus eventos de ratón.

De este modo:. (Esto supone que usted quiere guardar todas las rect de) - se puede ir con un solo rect al eliminar la ArrayList y reemplazar con una sola instancia rect

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;

public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {

    private static final long serialVersionUID = 1L;
    private final JLabel mousePosition;
    int x1, x2, y1, y2;
    int w, h;
    private final JLabel recStart;
    private final JLabel recStop;
    private final JLabel cords; // set up GUI and register mouse event handlers
    private final ArrayList< Rectangle > rectangles = new ArrayList< Rectangle >();
    private boolean isNewRect = true;

    public MouseTracker4July() {
        super( "Rectangle Drawer" );

        this.mousePosition = new JLabel();
        this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
        getContentPane().add( this.mousePosition, BorderLayout.CENTER );

        JLabel text1 = new JLabel();
        text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
        getContentPane().add( text1, BorderLayout.SOUTH );

        this.recStart = new JLabel();
        getContentPane().add( this.recStart, BorderLayout.WEST );

        this.recStop = new JLabel();
        getContentPane().add( this.recStop, BorderLayout.EAST );

        this.cords = new JLabel();
        getContentPane().add( this.cords, BorderLayout.NORTH );

        addMouseListener( this ); // listens for own mouse and
        addMouseMotionListener( this ); // mouse-motion events

        setSize( 800, 600 );
        setVisible( true );

    }

// MouseListener event handlers // handle event when mouse released immediately after press 
    public void mouseClicked( final MouseEvent event ) {
        this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );

        repaint();
    }

// handle event when mouse pressed 
    public void mousePressed( final MouseEvent event ) {

        this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );

        this.recStart.setText( "Start:  [" + this.x1 + ", " + this.y1 + "]" );

        repaint();
    }

// handle event when mouse released after dragging 
    public void mouseReleased( final MouseEvent event ) {
        this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );

        this.recStop.setText( "End:  [" + this.x2 + ", " + this.y2 + "]" );

        Rectangle rectangle = getRectangleFromPoints();

        this.rectangles.add( rectangle );

        this.w = this.h = this.x1 = this.y1 = this.x2 = this.y2 = 0;
        this.isNewRect = true;

        repaint();
    }

    private Rectangle getRectangleFromPoints() {
        int width = this.x1 - this.x2;
        int height = this.y1 - this.y2;
        Rectangle rectangle = new Rectangle( width < 0 ? this.x1
            : this.x2, height < 0 ? this.y1
            : this.y2, Math.abs( width ), Math.abs( height ) );

        return rectangle;
    }

// handle event when mouse enters area 
    public void mouseEntered( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

// handle event when mouse exits area 
    public void mouseExited( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse outside window" );
        repaint();
    }

// MouseMotionListener event handlers // handle event when user drags mouse with button pressed 
    public void mouseDragged( final MouseEvent event ) {
        this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();

        this.isNewRect = false;

        repaint();
    }

// handle event when user moves mouse 
    public void mouseMoved( final MouseEvent event ) {
        this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

    @Override
    public void paint( final Graphics g ) {
        super.paint( g ); // clear the frame surface 
        g.drawString( "Start Rec Here", this.x1, this.y1 );
        g.drawString( "End Rec Here", this.x2, this.y2 );

        Rectangle newRectangle = getRectangleFromPoints();
        if ( !this.isNewRect ) {
            g.drawRect( newRectangle.x, newRectangle.y, newRectangle.width, newRectangle.height );
        }

        for( Rectangle rectangle : this.rectangles ) {
            g.drawRect( rectangle.x, rectangle.y, rectangle.width, rectangle.height );
        }

        this.cords.setText( "w = " + this.w + ", h = " + this.h );

    }

    public static void main( final String args[] ) {
        MouseTracker4July application = new MouseTracker4July();
        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    }

} // end class MouseTracker

Answer 3

Lea sobre estos dos Custom Painting Enfoques . Un enfoque se ha descrito anteriormente y el segundo enfoque muestra cómo utilizar una BufferedImage. El ejemplo utilizado para ambos enfoques le permite añadir múltiples rectángulos al marco.

Answer 4

Si no se preocupan poco de información en pantalla, basta con borrar todos los "mousePosition.setText (...)" en los oyentes de ratón, que darán como resultado el repintado innecesaria () llamados.

A continuación, añadir dos campos: "int rx, ry;", añadir / modificar varios métodos como a continuación:

        public void mouseDragged(MouseEvent event) {
//      mousePosition.setText("Dragged at [" + (x = event.getX()) + ", "
//              + (y = event.getY()) + "]");
        // call repaint which calls paint
        x = event.getX();
        y = event.getY();

        compRectPos();
        repaint();
    }

    private void compRectPos()
    {
        rx = x1;
        ry = y1;

        w = x - x1;
        h = y - y1;

        if ( w < 0)
            rx += w;
        if (h < 0)
            ry += h;

        w = Math.abs(w);
        h = Math.abs(h);

    }

    public void paint(Graphics g) {
        super.paint(g); // clear the frame surface
        g.drawString("Start Rec Here", x1, y1);
        g.drawString("End Rec Here", x, y);

        g.drawRect(rx, ry, w, h);

        cords.setText("w = " + w + ", h = " + h);
    }

El único problema que encontramos es, que el rectángulo no aparece cuando se dibuja en primer lugar.