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Thread: Drawing on a swing frame

  1. #1
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    Default Drawing on a swing frame

    Hello everyone!


    I've recently tried to get swing frames working but the obstacle now is that I want to be able to move a rectangle on the screen.

    My first step was creating a rectangle which got drawn at the start on mouse x and y position:

    import javax.swing.SwingUtilities;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.BorderFactory;
    import java.awt.Color;
    import java.awt.Dimension;
    import java.awt.Graphics;
    import java.awt.*; 
    import java.awt.MouseInfo;
     
    public class MainWindowtestagain {
     
     
        public static void main(String[] args){
     
     
     
                    SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    createAndShowGUI();
                }
            });
     
     
     
            }
                        private static void createAndShowGUI(){
                  System.out.println("Created GUI on EDT? "+
                   SwingUtilities.isEventDispatchThread());
                   JFrame f = new JFrame("Swing Paint Demo");
                  f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                  f.add(new MyPanel());
                  f.pack();
                  f.setVisible(true);
                    }
    }
     
     
    class MyPanel extends JPanel {
     
        public MyPanel() {
            setBorder(BorderFactory.createLineBorder(Color.blue));
        }
     
        public Dimension getPreferredSize() {
            return new Dimension(640,480);
        }
     
     
        ////
     
     
        ////
     
     
     
     
     
        public void paintComponent(Graphics g) {
            super.paintComponent(g);    
            int rectx=77;
            int recty=66;
     
            // Draw Text
          //g.drawString("("+xpos+","+ypos+")",xpos,ypos);
     
                PointerInfo a = MouseInfo.getPointerInfo();
    Point b = a.getLocation();
    int x = (int) b.getX();
    int y = (int) b.getY();
            g.setColor(Color.black);
            g.drawString("This is my custom Panel!",10,20);
            g.setColor(Color.red);
            //g.drawRect(x/*x1*/, y/*y1*/, 32/*x2*/, 32 /*x2*/);
            g.drawLine(x, y-32, x+32, y-32);
            g.drawLine(x, y, x, y-32);
            g.drawLine(x+32, y, x+32, y-32);
            g.drawLine(x, y, x+32, y);
     
            g.setColor(Color.cyan);
            g.drawLine(140, 90, 86, 349);
            g.drawString(x+"  "+y,32,16);
     
     
        }
     
        }
        }

    but then I wanted it to happen every step so I tried to create a loop:
    import javax.swing.SwingUtilities;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.BorderFactory;
    import java.awt.Color;
    import java.awt.Dimension;
    import java.awt.Graphics;
     
    import java.awt.*; 
    import java.awt.MouseInfo;
     
    public class MainWindowtestagain {
     
     
        public static void main(String[] args){
     
     
     
                    SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    createAndShowGUI();
                }
            });
     
     
     
            }
                        private static void createAndShowGUI(){
                  System.out.println("Created GUI on EDT? "+
                   SwingUtilities.isEventDispatchThread());
                   JFrame f = new JFrame("Swing Paint Demo");
                  f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                  f.add(new MyPanel());
                  f.pack();
                  f.setVisible(true);
                    }
    }
     
     
    class MyPanel extends JPanel {
     
        public MyPanel() {
            setBorder(BorderFactory.createLineBorder(Color.blue));
        }
     
        public Dimension getPreferredSize() {
            return new Dimension(640,480);
        }
     
     
        ////
     
     
        ////
     
     
     
     
     
        public void paintComponent(Graphics g) {
            super.paintComponent(g);    
            int rectx=77;
            int recty=66;
     
            // Draw Text
          //g.drawString("("+xpos+","+ypos+")",xpos,ypos);
            int ii = 0;
            while (ii < 234823)
            {
                PointerInfo a = MouseInfo.getPointerInfo();
    Point b = a.getLocation();
    int x = (int) b.getX();
    int y = (int) b.getY();
            g.setColor(Color.black);
            g.drawString("This is my custom Panel!",10,20);
            g.setColor(Color.red);
            //g.drawRect(x/*x1*/, y/*y1*/, 32/*x2*/, 32 /*x2*/);
            g.drawLine(x, y-32, x+32, y-32);
            g.drawLine(x, y, x, y-32);
            g.drawLine(x+32, y, x+32, y-32);
            g.drawLine(x, y, x+32, y);
     
            g.setColor(Color.cyan);
            g.drawLine(140, 90, 86, 349);
            g.drawString(x+"  "+y,32,16);
     
            ii+=1;
     
            }
        }
     
        }

    but the program refused to show the images until i closed it, must be some sort of lag.

    What should I do?


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Drawing on a swing frame

    The code in the paintComponent() method should draw what its been told to draw and then exit as quickly as possible for the GUI thread to then get control back and make what was drawn visible on the screen.
    There should NOT be a long running loop in the paintComponent() method holding up returning control to the GUI drawing code in the jvm.

    See the tutorial about custom painting:Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing)
    If you don't understand my answer, don't ignore it, ask a question.

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