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Thread: Making a JPanel opaque, but showing paintComponent contents?

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    Default Making a JPanel opaque, but showing paintComponent contents?

    In my Independent Study class, I'm working on making a 2d scrolling platform game with my classmate. We're just starting out on this project and we think it'll be a huge help with learning to use the paint methods and basic game design, but we're already running into a bit of an issue. We've created a JFrame and set the background to a static, non-changing image, and we're trying to create a foreground JPanel which will contain the scrolling "platforms" which will be what our character will jump on. In order to do this, I believe we will need to make everything on the jpanel transparent, apart from the paitnComponent contents (which will be the platforms, I think). If we don't do this, wouldn't the jpanel show up as a white box and block the background image, or am I mistaken on that? Anyway, the code is below. Is there any way to have a transparent jpanel, but have the paintComponent contents still show up? Currently, all that I can see when I run the program is the background, with no black rectangle at the top.

    P.S. sorry if the formatting is a little whacked out. Transferring the code from my school computer to my home computer on google docs was a terrible idea.

     
        import java.awt.*;
        import javax.swing.*;
        import javax.imageio.*;
        import java.io.*;
     
        class BackgroundTesting extends JFrame {
            BackgroundTesting() {                                                       //Main JFrame, contains the BG and
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);                         //JPanel "JPan"
                setResizable(false);
                setSize(900, 447);
                setLocationRelativeTo(null);
     
                JPanel panel = new JPan();
                add(panel);
     
                setVisible(true);
            }
     
     
            public void paint(Graphics g) {
                Image img;
                try {
                    img = ImageIO.read(new File("/Users/java/Desktop/BG.png"));         //Sets image "BG" to the
                g.drawImage(img, 0, 0, null);                                           //Background of the JFrame
     
                } catch(Exception e) {}
     
     
            }
        }
     
        class JPan extends JPanel {
            JPan() {
                setOpaque(false);
                setSize(900, 447);
                setVisible(true);
            }
     
            public void paintComponent(Graphics g) {                                    //Will contain the "scrolling"
                g.fillRect(50, 50, 25, 25);                                             //Platforms
            }
        }
     
        class Frame {
            public static void main(String[] args) {
                BackgroundTesting bgTest = new BackgroundTesting();
            }
        }


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    Default Re: Making a JPanel opaque, but showing paintComponent contents?

    Please read the Custom Painting tutorial for a better understanding of Swing's painting mechanism. Your better understanding should lead you to correct some errors in your code that are either causing or contributing to the results you're seeing. After that, a Google search should help you find basic Java tutorials for side scroller games to get you started on a firmer foundation.

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    Default Re: Making a JPanel opaque, but showing paintComponent contents?

    Quote Originally Posted by NuclearCherry View Post
    In my Independent Study class, I'm working on making a 2d scrolling platform game with my classmate. We're just starting out on this project and we think it'll be a huge help with learning to use the paint methods and basic game design, but we're already running into a bit of an issue.
    In your code there are at least 2 things that are bad.

    1) Painting directly into JFrame is (generally) a bad choice. JFrame is complex, it contains a JRootPane which in turn contains the well known "content pane". Painting directly into JFrame, you are painting "behind" these components.

    2) Don't load images (in general any "resource") into a paint/paintComponent! These methods can be called thousand of times.
    Andrea, www.andbin.net SCJP 5 (91%) SCWCD 5 (94%)

    Useful links for Java beginners My new project Java Examples on Google Code

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