A Moogle  🏳️‍🌈 💻 🎮 🎶 🇸🇪

So is the middle window the alternate part of the FB, for the "palette" box thingy?

Yes - the middle screen is the palette mixing area - you'd have a grid of colours and then be able to mix paint in the large central white area with the painting brush you'd chosen.

I was wondering more about whether that screen is a different part of the framebuffer, or the other set of three boards. ;) IIRC, there are six FB boards. One set for Y,U,V, and another set for the back buffer.

There were definitely two frame stores available at the same time as you could use a 'reveal' brush to paint one into the other.

Yeah, that's what we're seeing in that screenshot. Rather than emulate the Combiner Card just yet, I'm simply chucking the monitor window, Frame Store I contents, and Frame Store II contents on-screen side-by-side, for debugging purposes.

Yes - the palette and menu could be overlaid over the top or the bottom of the video image (for obvious reasons)

Right. Each frame store had a usable 800x600 area, but during scanout, either the top 128 lines or bottom 128 lines would be fixed to scan out the palette or menu region rather than the corresponding lines in the store.

Pretty certain Paintbox didn't internally scale on input and output (particularly as it handled interlaced video)