As Tom said, you can't do layout or prerendering-to-bitmap in a web worker: there's no DOM or Canvas API unless you bring your own, and despite Emscripten it's foolhardy to bring your own. If you want to decode a JPEG, you have to do that on the main thread and pass it to the worker right now (except in Firefox with its nonstandard ImageData API). [0] Which brings us back to square one.
> no one ever comes close to native widgets
I think a lot of that has to do with the fact that the iOS UIKit internal code for animations is closed source - the best anyone can do is reverse engineer, move their thumb and see how things react. What are the Bezier points on the curve used for the fade when you "back-swipe" from the left of the screen? Good luck figuring that out - it's possible, but only barely. Tom hinted at the idea that if developers were better organized, they might be able to replicate things better, but it would still be an uphill battle.
The curves used in iOS are all pretty standard, they're easily to replicate if you want.
It's pretty easily to replicate iOS functionality in iOS itself just because it's a better environment, it's not the 'secret' numbers.
But if taking the example of Paper, it's built on top of Pop which is absolutely open source and handles all the animations: https://github.com/facebook/pop.
So in theory you should be able to replicate all this stuff on the web, but you can't because it's just not build with highly responsive UI in as the focus.
Since you are in native you could decode in native in a different thread and pass the decoded data into the Webview, but not sure if thats really better since you would still have to create an image object from the raw bitmap data.
As Tom said, you can't do layout or prerendering-to-bitmap in a web worker: there's no DOM or Canvas API unless you bring your own, and despite Emscripten it's foolhardy to bring your own. If you want to decode a JPEG, you have to do that on the main thread and pass it to the worker right now (except in Firefox with its nonstandard ImageData API). [0] Which brings us back to square one.
> no one ever comes close to native widgets
I think a lot of that has to do with the fact that the iOS UIKit internal code for animations is closed source - the best anyone can do is reverse engineer, move their thumb and see how things react. What are the Bezier points on the curve used for the fade when you "back-swipe" from the left of the screen? Good luck figuring that out - it's possible, but only barely. Tom hinted at the idea that if developers were better organized, they might be able to replicate things better, but it would still be an uphill battle.
[0] https://developer.mozilla.org/en-US/docs/Web/API/Worker/Func...