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Performance would always be my key concern with something like a general-purpose constraint solver. I know that LP is a field in its own right, but I don't have a ton of experience there -- do you think there's a practical path to bringing the performance up to a necessary level (i.e. real-time, <10ms calculation times for complex pages)?

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Perf is surprisingly good, suitable for modern web apps. The bottleneck is DOM & CSS selector resolution, not the constraint solver - Cassowary is a beast!

We're working on a lib for pre-computing GSS layouts server-side, but it's significantly more hardcore than traditional pre-processing.

What we really need is browser vendors to offer deeper API hooks into layout lifecycle, painting, etc

Did you or someone else ever try combining it with React? Because of the virtual DOM, it'll probably mean that you won't need CSS selector resolution at all. Not sure here - I don't know how the solver gets its input (e.g. how you compute which elements impact which ones - do you read existing offsets and sizes from the browser DOM, or do you do something different?). But somehow I feel that the constraints story and React's render-only pipeline should somehow be able to work together really well.

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