Flashing Phantom Elements?

[guppy]

Can someone who is in the know tell me why sometimes elements on the NES flash in and out of existence. A solid example is when walking. As the camera pans, part of the screen's elements will flash in/out of existence. I figured this is a memory issue, but wanted to know explicitly if anyone knows why. Gimmie da facts, man!

 

[sandogma]

I am not in the know so I'll defer to others who claim they are who chime in, but I do like learning about these kinds of things, so I took this as an opportunity and hopefully can share what I've learned.

The NES’s Picture Processing Unit (PPU), which generates the 2D video signal, has a built-in limitation that restricts it to displaying only eight sprites per scanline. This means that if a game tries to render more than eight sprites on a single horizontal line of pixels, only the first eight will appear, causing some sprites to disappear as the NES tries to cycle through them. This limitation is often referred to as the "8-sprite-per-scanline limit".

There is a technique where the PPU and CPU work together in reordering sprite data to alter the priority of the sprites on each scanline which causes the sprites to flicker instead of having some disappear entirely, this technique is referred to as Sprite Cycling, or OAM Cycling, as the OAM (Object Attribute Memory), which is part of the PPU, is involved.
Left image - no Sprite Cycling
Right image - Sprite Cycling implemented

Source: https://www.nesmakers.com/index.php?threads/4-1-5-sprite-cycling.2455/
Source: https://www.nesdev.org/wiki/PPU_rendering

 

[guppy]

Oooo, thank you Sandogma =)! I was thinking about this mostly on account of the GBC having more power than the GB and I knew this showed in the amount of space that could be rendered er...offscreen I suppose? Which I figured had to play into something with the NES. As it was an earlier system, and probably had a similar limitation. But it wasn't anything I actually knew about. And I didn't think this was tearing where pieces of imagery kinda lean one way or another. But also figured I could be wrong because I know nothing about ANY of it =P!

Thank you for this blurb as a whole. It helps me sort out some bits in the brain. I'd click through those links, but I apparently have a "spooky car ride" waiting for me =P! Big hugs!