The engine as it is today is a fantastic basis and fills most of our users needs. However, it also has a couple of shortcomings and problems that will need to get solved in the future. This series of blogs is going to outline our findings and present the solutions that we are planning to implement for them. The goal will be to get to a better, more flexible and easier to maintain QML engine in the future.
So let's start of with some of the problems we're facing with the current engine.
These different arguments have lead to a research project that was started Roberto Raggi and Aaron Kennedy in Nokia around a year ago, where they explored the feasibility of having a JS engine that is tailored to the use cases QML requires. The project with the codename v4vm was then transferred to Digia, where Simon, Erik and myself took it up and continued with it. It lived as a playground project on qt-project.org for the last couple of months.
Today we integrated this research project into a development branch of Qt Declarative, and we will continue to work on it there from now on.
The new engine contains a fully compliant ECMAScript 5.1 implementation, that runs on all platforms Qt supports. It contains a JIT that currently works on Linux, Mac and iOS. Integration into the current QML engine is currently done through a V8 compatible API layer which we plan to remove in the coming weeks. The engine can run all Qt Quick demos (with some minor glitches).
One of the things to note is that the engine is focused at QML use cases. This implies that we expect QML performance to become a lot better then it is today. Pure JS performance will on the other hand not be quite as good as what you get with V8 as a backend.
Still our current benchmark numbers are very promising also for pure JS code. The V8 benchmark runs currently around three times slower than the JS engine used in Qt 4.8 and Qt Quick 1, and we see a lot of potential for further optimisations.
Details about the new engine and our future plans will come in a followup post. You can find the code in the wip/v4 branch in the qtdeclarative repository. Feel free to play around with it. If you want to join development, feel free to contact us on #qt-v4vm on freenode.
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