Ways to manipulate or dynamically shift/mask images

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I have been into demo scenes as of recently.
(My favorite one being Titan - Overdrive 2 for the Sega Megadrive / Genesis).
As of late, I have been thinking about what should be my next small project should be for my little Learning Series of trinkets.

For my next one, I want to figure out how to do this -> Earthbound Battle Backgrounds but also render a masked image in its own circle radius. (Think of it like a image inside of a circle moving around but not going outside of the circle going into the background).

As I was researching this I came across a problem. How am I supposed to render something that doesn't exist on screen? More importantly, How do I even handle manipulating such a large scale effect on a device like this without performance hiccups.

I wanted to see if anyone has came up with ways to do this.

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You can do this with pattern and mask. The pattern will limit you to 8x8 repeating pattern.

See https://devforum.play.date/t/matts-prototypes/826/3 where I do it - without mask - by drawing on a single line rectangle to get the classic "marching ants" effect.

If you need a larger repeating pattern then you can use an image table and mask.

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Ooo, this looks extremely interesting!

I am thinking about drawing and offsetting an image 1 pixel at a time to do the wavy effects. Then playdate.update().
Not sure if this is the best solution but its a method I came up with while day dreaming at my job.