Thread: 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...

Show us the paintComponent() method. You may have made a small mistake there.

Heh, it's not much:

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

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.

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)

Exactly as I found. Thank you for your help!

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.

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

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);
  }

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