Each time each image in the lightbox loads, it re-renders w…

Samuel 25 Jan

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Samuel 25 Jan

moving my brain dumping thread here. I think there’s two issues at play w.r.t. perf

Samuel@samuel.fm· 25 Jan

I tried putting it behind useDeferredValue, but it didn't do anything as it seems like the scroll handler has an unstable identity for no good reason

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Samuel 25 Jan

1. List component rerendering. we need to change a scrollview prop on iOS. I already scoped this to iOS-only, so it’s not a perf concern on Android, but it’s got a massive over-render problem. changing this one tiny prop causes every list item to rerender, which is ridiculous

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Samuel 25 Jan

Easy solution - take my existing useScrollsToTop hook, and put a useDeferredValue on it. therefore we can defer this nonsense until after the lightbox has finished rendering alas no. List rerender anyway. Profiler blames onScroll, and I added logging and yeah it changes on that initial ctx change

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Samuel 25 Jan

I’m pretty sure it’s just unstable, I.e. different identity on each render, which shouldn’t be the case - it’s not doing anything here! next step is to narrow down what’s causing it to change. Reanimated has some magical auto-dep-array stuff which is probably to blame - likely doesn’t mesh w/ RC

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Samuel 25 Jan

2. Slow on Android Perf on Android is still unacceptable, especially for 2+ images. I have yet to dig in but I have speculation. the animation gets triggered in a requestAnimationFrame. I’m guessing the main thread is getting locked up so it has to wait a really long time?

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Samuel

@samuel.fm

Each time each image in the lightbox loads, it re-renders with its image dimensions. So we have 4 fairly heavy components (each image) rendering invisibly before the animation can begin, and each one re-renders as they load. maybe the animation is queued behind that whole process?

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Samuel 25 Jan

what I will try is deferring rendering the other 3 images until after the animation is complete. they’re being prefetched already so it shouldn’t cause any functional changes?

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Francis 25 Jan

Sam it's Sunday night why are you thinking and writing about work, don't