On a fresh boot of pico-8, this glitchy grid effect happens exactly once, the first time that secret colors are used in a screen palette. Then never again.

I discovered this in my latest cart, and was wondering if this is an intentional indicator of "hardware mode change", or a bad sign that something is going seriously wrong. The starting palette of this cart uses only normal 0-15 colors, as does the "raw" palette you see when you press up. However, every other palette will show this glitch once for about 0.5 seconds, before the screen returns to normal. Re-running the cart does not show it ever again, until you reboot pico-8 completely.

Using if(pi==3) poke(0x5f2e,1) stop() poke(0x5f2e,0) at the end of the _draw function means that the effect will happen for the same amount of time without any game code running at all, which makes me think that this visual glitch is intentional. Note also that without the poke to make the screen palette persist in the editors, there is no glitch effect, likely because it doesn't flip() with secret colors active. Any idea why this is happening, @zep?

Just to let you know, @shy, it's something ZEP WANTED to have - to show that some Piconian was using the extended palette. There was a big discussion about this years ago.

If you plan to use the extended palette, it's best to get that silly glitch out of the system as early as possible. Something like:

function _init()
  pal(0,128,1)
  pal(0,0,1)
  ... rest of your init code
end

Ah, fair enough. Yeah, it's easily fixable, but since this is an experimental cart I don't mind if the glitch stays. Just wanted to make sure it wasn't a more serious backend bug.

I encountered this today. Interesting to read the glitch is intentional. Good to know, now I can decide whether to "get it out of the way" in init, or leave it cause it looks cool and old and glitchy. <3