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Comment by rubymamis | Hacker News Reader

BTW, someone created Flexbox for QML: https://github.com/tripolskypetr/qml-flexbox

It's really awesome someone did this. If you just want the expressiveness of flexbox and don't care about performance, this is perfect!

However, wouldn't the performance for this be very optimal? Check out the `Flex.qml` code[1]. It's all very unoptimized and dynamic QMLScript. None of the function arguments are typed. There is no way the QML compiler is turning any of this into efficient, statically typed C++ code. The beauty of using flexbox in the browser is that all the layout calculations are done natively in the browser without ever touching JavaScript.

[1] https://github.com/tripolskypetr/qml-flexbox/blob/master/qml...

Nope, from what I can tell the entire backend is a Qt C++ binding[1] for the C++ Yoga library[2][3]. You can see the Qt C++ backend is exposed to QML here[4]. So it's C++ all the way down just in a comfortable setting.

[1] https://github.com/tripolskypetr/qml-flexbox/blob/master/obj...

[2] https://github.com/tripolskypetr/qml-flexbox/tree/master/thi...

[3] https://github.com/facebook/yoga

[4] https://github.com/tripolskypetr/qml-flexbox/blob/677a1287df...

P.S. I'll answer your other reply very soon. I'm releasing a new version of my app so it takes its toll on me.

Whoops, I should have been more clear. When I said "It's all very unoptimized and dynamic QMLScript" I meant just the file `Flex.qml`. I'm sure the Qt C++ bindings are fast and great, but check out the `updatePositions` function in `Flex.qml`[1]. This unoptimized and dynamic QMLScript gets ran every time a flex item's width, height, or children change. I imagine if that QMLScript was given types then at least that QMLScript compiler could generate some C++ for it, but right now there are no types so I doubt there is any efficient C++ generated for this script.

On the web it's common to animate the size of flexbox items with CSS animations. These animations are entirely implemented by the browser, and I imagine much of it is even GPU accelerated. No JavaScript is executed for this on the browser. But with this library, you would be running the `Flex.qml`'s `updatePositions` function every frame of the animation. Isn't that wasteful when compared to how flexbox works in the browser? It seems like a browser would be much faster at computing layout for flexbox elements than this, especially when that flexbox's size is being animated with CSS animations.

[1] https://github.com/tripolskypetr/qml-flexbox/blob/master/qml...

Hmm I get your point. I wonder if the the QML type compiler (qmltc) could still compile to C++. It would seem like dark magic if it did tho, because as you said it hasn't given the types. I wonder if it's possible to put this code in the backend in C++, what do you think?

> I wonder if it's possible to put this code in the backend in C++, what do you think?

Yeahh, looks like you'd have to connect to all these signals and be able to access sizing/position from C++. Not sure how possible this is, you probably know better than me.

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