Don't use background()... the PGraphics will default to fully transparent.
If you have to reset the PGraphics to be transparent, and background() doesn't work, then loop through all of the pixels and set them to be transparent.

I don't think get() should cause a problem... but why can't you just pass the PGraphics to image()?

As calsign said...
But IIRC, get() indeed looses the alpha information.
But, again, you don't need to use get(), do you?

Demo:

1. void setup()
2. {
3.   size(400, 400);
4.   background(#55AAFF);
5.  
6.   PGraphics off = createGraphics(200, 200, JAVA2D);
7.   off.beginDraw();
8.   off.fill(#00AA55);
9.   off.ellipse(50, 50, 100, 100);
10.   off.endDraw();
11.  
12.   image(off, 100, 100);
13.  
      copy(off, 5, 5, 50, 50, 300, 300, 50, 50); // If you need only a part of the image
    
14. }

Hi guys thanks for responding since both of you are wondering why I am using get() to copy the PGraphicsJava2D buffer to a PImage it might help if I explain what I am doing.

A while ago there was a post about simulating page-turning and there was a link to another webpage which discusssed the use of masks and symmetry and it got me thinking about creating a P5 sketch.

When I started the sketch I had 2 options

1. draw the images directly onto the main canvas using draw() i.e. in the main event thread.
2. use a seperate thread or timer to draw the images into a buffer and then use draw() to copy the buffer onto the main canvas.

I went for the second option because although it uses more resources it is also more flexible because the user can decide how to use the image created.

So I have solved the maths and program logic, and have a nice animation of a book where you can turn pages forwards and backwards. The picture shows an image created when the last page of the book is turned over.


The white area and the pages are the actual image obtained from the PGraphicsJava2D buffer.

The blue area is the main P5 window the buffer image has been has been drawn on with the image(PImage img, ...) function.

This is just 1 of the 200 frames needed for the full animation of a page turning. Each image is 800x600 pixels so a solution that loops through all the pixels is to be avaided.

I am using a Java Swing Timer object to generate action events whch are used to draw each frame into the buffer and then capture it into a PImage object using get()

The draw() method then copies the image directly into the window.

I am trying to create the buffer so that the white areas are transparent.

Since the image() method expects a PImage object as the source I have to use get() to create the PImage from the buffer. Looking at the source code the copy command should preserve the alpha data but only copies data within the PGraphics object so can't be used to copy from the buffer.

So it seems to me that if the problem lies with the get() method loosing the alpha values then there is no easy solution - unless anyone out there knows differently.

" Since the image() method expects a PImage object as the source I have to use get() to create the PImage from the buffer."
Wrong. Unless I missed something. As you can see from the sketch I posted, you can use a PGraphics in image(). Because PGraphics extends PImage!

@PhiL.ho
I had completely fogotten that PGraphics inherits from PImage and I should have looked more closely at your code example. It means that I no longer need the PImage object so I save on resources and the CPU time needed to copy to the PImage.

I now have my sketch working as I want (transparency preserved) so thanks for your help.