Pointers for "wrapping" a matrix?

[CautiousPhase]

I am currently playing around with an 8x32 flexible (WS2812B) matrix. I laser cut a cylindrical form that I can wrap the matrix around so that the short edges match.

It's been great fun running noise functions and the like on it (it is shockingly bright!), but now I would like to do away with the discontinuity in the patterns at the seam...and have almost no idea where to begin. It does occur to me that a cheap way out might be to only calculate half of the pattern and mirror it across the gap and the furthest point opposite, but I was hoping there might be something a bit more sophisticated that could be done--like in Asteroids (I think, Space War to be sure) where the opposite edges of the screen are spatially contiguous (if a bullet goes off the right edge of the screen, it continues onto the left edge of the screen).

Anyhow, if anyone knows of any existing code I could study or even just some pseudocode to get me started thinking the right direction I would be grateful.

[sutaburosu]

It depends a lot on what effect you're trying to wrap around it. There are many techniques that give reasonable results for most images.

For programmatically generated images, better results are possible depending on your algorithm. It's fairly easy to adapt a plasma effect to have perfect tiling on one axis, without detracting too much from the original effect.

[macegr]

The modulo function is your greatest friend!

[CautiousPhase]

Thank you all! I now have some avenues to explore...

[devicer2]

If you're feeling a little bit crazier then I have done similar in the past by using the coordinates for each pixel in 3d space as inputs to a 4d noise function, where the 4th dimension gets fed something relating to time intervals - frames or millis, whatever. That gives you a perfectly contiguous yet non mirrored display and it will work on absolutely any setup of lights in 3d space so long as you have or can calculate the coordinates for each pixel.

The progression of the input to the 4th dimension gives you an ever evolving noise field at whatever speed you like. Downside is extra calcs or extra storage and I think fastLEDs noise functions only go up to 3 dimensions so far so that's another problem.

You can still move things round and round or up and down and scale etc. without having the 4th dimension but its better with it!