Description

hx2A

opened on May 21, 2026

Issue body actions

Most appropriate sub-area of Processing 4?

Core/Environment/Rendering

Processing version

4.5.2

Operating system

Linux (Unbuntu) and MacOS Tahoe

Bug description

I get a null pointer exception when I pass a PGraphics object to the background() method.

For some reason the PDE doesn't display the stack trace, I just see this:

NullPointerException
NullPointerException

Steps to reproduce this

The example code below reproduces the bug.

snippet

PGraphics g;

void setup() {
  size(300, 300, P3D);
  
  g = createGraphics(width, height, P2D);
  g.beginDraw();
  g.background(0, 255, 0);
  g.endDraw();
}

void draw() {
  background(g);
}

I am able to get a stack trace when I use the equivalent code in py5. I traced the problem to the PGraphics object's null pixels array.

One possible workaround is to insert a g.loadPixels() call after g.endDraw(). That fixes the problem. Another workaround is to get() a PImage object:

PGraphics g;
PImage img;

void setup() {
  size(300, 300, P3D);
  
  g = createGraphics(width, height, P2D);
  g.beginDraw();
  g.background(0, 255, 0);
  g.endDraw();
  img = g.get();
}

void draw() {
  background(img);
}

Additional context

Either workaround suggests a solution. I'm happy to make a PR to fix this, you can assign it to me.

Would you like to work on the issue?

Yes, I’d like to help with this

Activity

1. hx2A

   added

   bugSomething isn't workingSomething isn't working

   on May 21, 2026
2. catilac

   assigned

   hx2A

   on Jul 13, 2026
3. catilac commented on Jul 13, 2026

   

   catilac

   on Jul 13, 2026

   Collaborator

   More actions

   Thanks @hx2A! Assigned to you.
4. hx2A commented on Jul 15, 2026

   

   hx2A

   on Jul 15, 2026

   ContributorAuthor

   More actions

   Thank you @catilac ! This bug fix is pretty straightforward and I'll get it done.

   Reacted by Raphaël de Courville, Moon and Xin Xin
5. catilac commented on Jul 15, 2026

   

   catilac

   on Jul 15, 2026

   Collaborator

   More actions

   thanks @hx2A really appreciate your help :)
6. hx2A

   changed the title [-]`background()` method throws `NullPointerException` for `PGraphics` objects[/-] [+]`set()` method throws `NullPointerException` for `PGraphicsOpenGL` objects[/+] on Jul 31, 2026
7. hx2A commented on Jul 31, 2026

   

   hx2A

   on Jul 31, 2026

   ContributorAuthor

   More actions

   Renaming this because I see void backgroundImpl(PImage image) calls set(0, 0, image), and I can reproduce the bug with set(0, 0, g) also. And this bug only applies to PGraphicsOpenGL instances.
8. hx2A commented on Jul 31, 2026

   

   hx2A

   on Jul 31, 2026

   ContributorAuthor

   More actions

   I created a PR for this, it is running the checks.

   #1557

   Here is test code:

   PGraphics g;
   
   void setup() {
     size(300, 300, P3D);
     
     g = createGraphics(width, height, P2D);
     g.beginDraw();
     g.background(0, 255, 0);
     g.endDraw();
   }
   
   void draw() {
     // background(g);
     set(0, 0, g);
   }
9. hx2A commented on Jul 31, 2026

   

   hx2A

   on Jul 31, 2026

   ContributorAuthor

   More actions

   Other permutations of renderer type or graphics type don't experience the problem. The bug only appears when both the Sketch and the graphics object are PGraphicsOpenGL instances. The bug is triggered with background() or set().
10. catilac

    closed this as completedin c83c84aon Jul 31, 2026
11. hx2A commented on Jul 31, 2026

    

    hx2A

    on Jul 31, 2026

    ContributorAuthor

    More actions

    Awesome, thank you for merging @catilac

    Next up, #1422

    Reacted by Xin Xin
12. pull

    added a commit that references this issue on Jul 31, 2026

    fix processing#1520 (processing#1557)

    This issue will close once commit c83c84a is merged into the 'main' branch.

    c83c84a

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