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Comment by rpedela | Hacker News Reader

I'm an old 3d graphics programmer. One of performance rules is only render what will be displayed in that frame because rendering is expensive. That is why there are various culling algorithms, some are quite complicated. The reward for implementing all these advanced culling algorithms is very fast frame renders that give you more time to draw special effects, draw more characters, etc in a single frame.

I am a data engineer now and sometimes have to build web interfaces for scrolling large data tables. Just like in the 3d graphics world, the trick to responsiveness is culling. Only download and display the amount of data that the user will see at a given time, plus some overhead so the user never sees gaps when scrolling.

While Rust may have solved the problem in #1, it is unlikely to solve the problem in #2 because you are also fighting the network where Rust is useless. Need culling.

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Unfortunately because web content is automatically positioned/sized in a way that's (mostly) opaque to JavaScript code, this is a pretty hair problem (compared to graphics where you have all the numbers on-hand). So most of the time you'd either have to a) try and replicate the math the layout engine ends up doing which makes things more brittle, or b) directly measure the computed dimensions/positions/visibility/scroll position of different elements, which tends to be a pretty large performance liability and in many cases would eliminate any gains you might receive.

There are some edge cases where these techniques can work - like if you have a really simple layout, and you can give a fixed-height to every item (table row or otherwise), and you assume the user is never going to resize their browser window - but it isn't nearly as obvious of a win as it is for 3D rendering and we just never decided it was worthwhile to try going down that rabbit-hole.

> Unfortunately because web content is automatically positioned/sized in a way that's (mostly) opaque to JavaScript code, this is a pretty hair problem (compared to graphics where you have all the numbers on-hand).

Exactly the same for 3d graphics. The auto-positioning is different but conceptual similar.

Yes B is my recommended approach. Since we are talking about performance, we should really be putting limits on what fast and slow mean. That is because it doesn't really matter if something is fast or slow, what matters is the performance difference between different approaches.

For B on average, performance will in the microsecond range, DOM rendering will be in the millisecond range, and the network is >100ms to seconds range. It is unlikely that B will be equal or slower to brute force rendering everything. Those X microseconds spent figuring out the culling window saves Y milliseconds rendering and saves Z milliseconds to seconds querying the network.

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