Although the following code works for PGraphics3 it doesn't with PGraphicsGL:
Code:

import processing.opengl.*;
PGraphicsGL graphic;
void setup(){
  size(400, 400, OPENGL);
  graphic = new PGraphicsGL(width, height, this);
  graphic.defaults();
  graphic.background(255);
}
void draw(){
  graphic.line(0,0,width,height);
  image(graphic,0,0);
}
 

I want to be able to use smooth(), hence the need for a PGraphicsGL but I'm getting the following error:
Code:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at processing.opengl.PGraphicsGL$ImageCache.rebind(PGraphicsGL.java:882)
 

I'm guessing that because I can't find an implementation of PGraphicsGL on the forum there must be some voodoo involved to get it to work.

I basically just want to be able to draw something flat (no translation or matrix stuff) on to an off screen image but using smooth().

A thought:
What if you draw to the main GLCanvas as usual and then use glReadPixels to get the data back out (storing it in a PGraphics, for example). A lot of pixel-moving i know, but if fps isn't particularly important it might work.