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Thread: Painting Issues

  1. #1
    Member snowguy13's Avatar
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    Default Painting Issues

    Hello! I've been doing HTML for a while and now am returning to Java after a few months, and I can tell I've lost a few things...

    Right now, I'm trying to develop a very basic layout for an RPG. It will be the top-down view sort of RPG, and I have it working so that the arrow keys can be used to move around the screen. The only problem is the level won't paint. I have an extension of JPanel called LevelPanel that holds all the information for the player and the objects of a level, and a class called Renderer uses an instance of LevelPanel to draw the level. LevelPanel's paintComponent method is overridden to invoke the Renderer class's renderLevel method, which as I stated before draws the level, its objects, and the player. A JFrame is being used to hold the panel. The frame has a Swing Timer that fires every 1/40th of a second to update the display of the LevelPanel so that when the user moves or collects an item his/her action is seen.

    Unfortunately, nothing is drawn. I've put printlns throughout the Renderer class and they all get printed, but the frame is never painted upon.

    Renderer:
      public static void renderLevel(LevelPanel l) {
        Graphics g = l.getGraphics();
        Graphics2D g2 = (Graphics2D)g;
     
        System.out.println("Filling background");
        g2.setColor(Color.BLACK);
        g2.fillRect(0, 0, l.getLevel().getxSize(), l.getLevel().getySize());
     
        //drawing spawn
        System.out.println("Drawing spawn");
        g2.setColor(Color.GRAY);
        g2.fillOval(l.getLevel().getSpawnPoint().x, l.getLevel().getSpawnPoint().y, 10, 10);
     
        //drawing collectable objects
        System.out.println("Drawing objects");
        for(CollectableObject i : l.getLevel().getItems()) {
          i.draw(g2);
        }
     
        //drawing player
        System.out.println("Drawing player");
        l.getPlayer().draw(g2);
      }

    Is the panel not being drawn because repaints are being requested to often? I would find that odd, since I have another project that uses a similar concept and updates faster than this one...

    Am I missing something? Any suggestions would be appreciated...
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  2. #2
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    Default Re: Painting Issues

    Show us the paintComponent() method. You may have made a small mistake there.
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    snowguy13 (May 23rd, 2012)

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    Default Re: Painting Issues

    Heh, it's not much:

    public class LevelPanel {
      //... blah blah ... a lot of other code
      public void paintComponent(Graphics g) {
        Renderer.renderLevel(this);
      }
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    Default Re: Painting Issues

    Okay, this is utterly silly, but I found a solution.

    The renderLevel method declaration I switched to this:

    renderLevel(LevelPanel l, Graphics g)

    and then I switched the paintComponent method to

    Renderer.renderLevel(this, g);

    and now it works great. Odd.
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    Default Re: Painting Issues

    I'd recommend posting an SSCCE...I personally cannot tell what is or is not going on from what you posted. The one thing I can deduce is that it seems you are calling getGraphics() on what looks like a panel - drawing should occur on the Graphics object passed to paintComponent (I used to have a good example of why one shouldn't rely on getGraphics() - but can't find it at the moment - nevertheless you should rely on paintComponent, not getGraphics)

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    Default Re: Painting Issues

    Exactly as I found. Thank you for your help!
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    Default Re: Painting Issues

    Also, it is HIGHLY suggested that you call super.paintComponent(g); before calling the renderLevel method. You are already filling in the background in the renderLevel method, but it is considered a good habit. The API for it even cites some possible problems if it is overridden and the super is not called.
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    Default Re: Painting Issues

    If I'm calling repaint() in the LevelPanel class, will super.repaint() suffice if placed before the repaint() call?
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    Default Re: Painting Issues

    Maybe, but that is probably less memory-friendly, and it adds more pain if you want to trigger the repaint from other places later on.

    This is all you need to do:
    public void paintComponent(Graphics g) {
    super.paintComponent(g);    
    Renderer.renderLevel(this);
      }
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    snowguy13 (May 23rd, 2012)

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    Default Re: Painting Issues

    Oh, whoops -- I misunderstood you the first time. Yes, I will add that line of code. Thank you for your help!
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