What Im saying is, PJOGL profile 1, versus the new, 2, or whatever it is, actually behind the scenes renders differently. This is what you are seeing.
Your code does not call background every frame That choice exhibits different behavior between PJOGL versions.
What this means in practice behind the scenes is don’t clear your color buffer, and or your depth buffer. The result of how PJOGL 1 vs 2’s compositing, blend modes, alpha blending handling and default state, and what buffers are erased when you *do* call clear are all completely 100% dependent on whatever processing’s implementation of background is behind the scenes, and that background call might actually change behavior between versions of PJOGL that you use.
in other words, you don’t have control.
You can lean on the processing forums for ways to draw into frame buffers or draw into image objects efficiently without clearing them that works across renderers’s and doesnt rely on ‘not clearing’ your main drawing target.
In essence, I’m pretty sure you are relying behavior not guaranteed by processing’s compositing setup.
I’d be very surprised if this has ANYTHING to do with Syphon.