CODEWITHSUNDEEP
javagraphicstransparencyargb
Pierre
Pierre

Reputation: 35276

Filling with transparency using Graphics2D

I created an ARGB BufferedImage. Now I'd like to reinitialize it with a transparent background. I tried the following code:

(...) 
if( this.offscreen==null  ||
    this.offscreen.getWidth()!= dim.width ||
    this.offscreen.getHeight()!= dim.height )
    {
    this.offscreen=new BufferedImage(
       dim.width,
       dim.height,
      BufferedImage.TYPE_INT_ARGB);
     }
Graphics2D g=this.offscreen.createGraphics();
g.setColor(new Color(255,255,255,0));
g.clearRect(0, 0, dim.width, dim.height);
(...)

but it didn't work.

Any idea on how to do this please ?

Thanks !

Upvotes: 2

Views: 8078

Answers (2)

Mohammad Ali Saatchi
Mohammad Ali Saatchi

Reputation: 124

I had this problem before and I solved it with a really narrow trick. Here is the deal:

In the constructor of the paint Class take a screen shot of the System but be careful 

BufferedImage image = new Robot().createScreenCapture(new Rectangle(0, 23, xScreen, yScreen));

And where you want to clear the screen 

g2D.drawImage(image, null, /*your Image observer*/);

Upvotes: -1

Chris Dennett
Chris Dennett

Reputation: 22721

g.clearRect(..) fills the selected rectangle with the background colour of the Graphics2D object. You're better off doing g.fillRect(..) which would give the intended result with your code, or set the background colour of the Graphics2D object beforehand (g.setBackground(..)).

Also, you may have to do g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC)); before the fill so that it sets the buffer properly (ignore destination buffer data, only use source data -- in this case, the fill operation). Not sure what the default is for this value, but you should set it back to that afterwards to ensure proper operation.

Upvotes: 2

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