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  Double Buffering Problem  (Read 1213 times)
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Offline bert

Junior Devvie




Miles of road and miles of code


« Posted 2006-06-16 16:18:40 »

I've been working on a platform-style game with animation, sound fx and the whole nine yards. However, I am currently stumped. My main class extends JApplet, but every time I call createImage(int,int) on it, it returns null. How can I fix this?

PS- I really don't want to have to create it using a MemoryImageSource but if that's what it comes down to then I'll do that.

w00t, i'm winning
Offline Coinerson

Junior Devvie




Introducing the world's cutest zombie, Timmy


« Reply #1 - Posted 2006-06-17 07:15:27 »

Maybe show some code?
Offline CommanderKeith
« Reply #2 - Posted 2006-06-17 07:15:46 »

From the Component.createImage(int, int) API docs:

Returns: an off-screen drawable image, which can be used for double buffering. The return value may be null if the component is not displayable

Like with other JComponents, you have to call setVisible(true) on the JApplet before you can get an image.  This is annoying I know.  Its like how you get zero for the width or height of a component until you actually paint it.  Wink

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Offline bert

Junior Devvie




Miles of road and miles of code


« Reply #3 - Posted 2006-06-17 17:59:03 »

Thanks a lot! I also noticed that as soon as I put the applet into a Web page (making it visible) then the problem went away. I should have went straight for the API. (Boy, I feel like an idiot now.) But thanks so much, CommanderKeith!

PS- I tried making my applet visible before calling createImage() and I am no longer getting the NullPointerException. However, I got another NullPointerException at a later point in my code.  Undecided


int state;
public static final int MENU=0, MAINMENU=0;
ImageIcon[] menupix=new ImageIcon[5];
menupix[0]=new ImageIcon("mainmenu.jpg");
if(state==MENU) menupix[MAINMENU].paintIcon(this,g,0,0); //this line is the culprit


This is a (rather condensed) version of my code that's giving me a hard time. I've crawled through the API but could not find anything pertaining to the situation. It won't tell me what the NullPointerException is, either, but I'm pretty sure it's referring to the ImageIcon. This was called from a JApplet's Paint method. All of the declarations were outside of any methods I had. Setting menupix[0] was in my applet's init() method. Thanks a lot for putting up with me and my stupid questions.  Grin

w00t, i'm winning
Offline Anon666

Junior Devvie




aka Abuse/AbU5e/TehJumpingJawa


« Reply #4 - Posted 2006-06-19 14:50:39 »

Doubt it is the cause of your problem but to be technically correct (the best form of correct ;P), the filename should be :- "/mainmenu.jpg"

As for your specific problem, why don't you just use a debugger - and step through your code.

If I asked on a forum every time I got an ArrayIndexOutOfBoundsException or a NullPointerException, I would be forever asking questions on the forum.
This problem you have encountered is of your own creation, in your own code - short of posting your entire applications source-code and asking "can you fix this please", there is very little we here on the forum can help you with.
Part of being a programmer is learning how to fix your own mistakes.
Offline bert

Junior Devvie




Miles of road and miles of code


« Reply #5 - Posted 2006-07-08 18:06:05 »

Yeah, sorry. I got really frustrated that day and went on a posting frenzy in a huge burst of noob-anger.

w00t, i'm winning
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