Clearing graphics

Question

Hi everyone !
I'm using the Java Graphics2D API to create a Game Engine, I know how to draw sprites etc but I have a problem.
To refresh the screen, I'm using graphic buffers ( BufferedImage's ) and I have to clear them before redrawing the screen.
The engine is composed of 5 layers ( drawn one above an other ), so when I clear them I want to keep the alpha property of each one.
The method I wrote is here :
protected final void clear(Graphics2D g)
     Composite c = g.getComposite();          
     g.clearRect(0, 0, Tests.WIDTH, Tests.HEIGHT);
     g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_IN, 1f));
     g.setColor(new Color(0, 0, 0, 0));
     g.fillRect(0, 0, Tests.WIDTH, Tests.HEIGHT);
     g.setComposite(c);
}This is the only way I have found, but it is very slowly for a game engine.
Do you have a better idea to resolve this problem ?
Thanks in advance.

Answer 1

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Are you using compatible images? If not, using them will probably lead to a nice performance boost, especially if you're blitting lots of BufferedImages to the screen per frame.
BufferedImage img = canvas.getGraphicsConfiguration().createCompatibleImage(int width, int height, int transparency) ;Besides that little bit of advice, I'm still a little confused as to what you're trying to do, so an SSCCE would probably be best.
>
No I wasn't and I'm not using the Canvas class.
Nevertheless I have tried to create an image with the 'getGraphicsConfiguration' method of the JPanel I use to render the game, but a NullPointerException was thrown.
I so wrote a method with GraphicsEnvironement and GraphicsDevice class to get a GraphicsConfiguration and finally create a compatible image but the result
was not very conclusive.
The thing I'm trying to do is just to clear a BufferedImage without losing its alpha property. In fact, my engine ( a tile engine ) wroks with layers.
So if a layer background becomes opaque, the things that are under this layer ( another layer ) would not be visible.
But this method :
>
I'm pretty sure that the code you posted is equivalent to
Composite orig = g.getComposite();
g.setComposite(AlphaComposite.Clear);
g.fillRect(0, 0, Tests.WIDTH, Tests.HEIGHT);
g.setComposite(orig);
This wouldn't require the clearRect(). In fact the code you currently have doesn't require the clearRect(). Also, the CLEAR rule doesn't require any calculations like the SRC_IN rule.
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made my engine take twice less time to execute for each frame. ( 47ms instead of 94 before )
Thank you