It's time for a new progress note.

In last one I was talking about my attempt to optimize the chat history with Cagou on Android. Indeed, while scrolling through history is smooth on desktop, it's quite slow on Android (but not dramatic).

My plan was to use RecycleView, which is an optimized widget to show a big list of widgets.

But, as I've explained last time, RecycleView has troubles with widgets with dynamic height (which is the case for chat messages, height depends of content). While working on a workaround (the idea was to pre-render each widget without displaying them, and use the calculated size), I've realized that even RecycleView was not so smooth on Android, and that was complicating a lot the code.

So I took the (hard) decision to abandon this idea, it was taking too much time without perspective of good results. Sometimes it's a good thing to step back and save time for other things.

Instead, I've simplified a bit other parts of the code, and thanks to a blog post on Kivy website that I've read recently, I've used the idea of a delayed resize (the message history is complex to resize because there are many elements – messages with styling, images, avatars, nickname, timestamp, receipt flags, etc. –), meaning that when you resize the window or the messages widgets, the resize is not done immediately, but only after a short delay (replacing any previously delayed resize). This way you limit the number of size calculations, and the feeling is better.

Still there is room to improve perfs for chat history scrolling on Android, but that can wait, it's usable enough for now.

I've come across a ticket for python-for-android predicting a hard future on Android: background tasks are more and more difficult to run. I'm not sure how it will evolve and what will be the consequences for SàT, we'll see.

Still on the Kivy side, I've realized that a bug that I had on Android (issue when sliding chat widget with the Carousel) was fixed in dev version. As I have no idea when next version of Kivy will be released and I had to fix this issue immediately, I've done a backport of the dev version of Carousel in Cagou, which I'll remove as soon as the Kivy 2.0 is available.

I've moved to Python 3.8, and I've had to face a couple of troubles.

Twisted, which is a major component of the backend, is not yet Python 3.8 compatible. Fortunately, the issue and fix were easy, so I've reported the issue and proposed a fix.

It is not super pleasant to propose a fix to Twisted because you have to look into the doc (which is rather indigestible), create the ticket on their bugtracker – with a terrible UI – but with a Github account (I have one for contributions only, but I'm don't like to be forced to have it), do the fix, write a test – with a not so pleasant "Believe me, if you write your tests after you write your code, we will know. It's more obvious than you think." making you feel like a little pupil at school –, write a piece of text to generate the changelog automatically, and finally update the ticket to ask for review (then we'll follow usual change request/review until the patch get merged, rejected or abandoned).

On the bright side, the Twisted community is nice, and I have to admit that the code quality of Twisted is really good thanks to their test-driven development (and general competence of people working on it). I'm using Twisted since the beginning of SàT (without any regret so far), and I really love the stability of its API, and that I'm rarely crossing the way of a blocking bug. I just have the feeling that it could be more contributors friendly.

For the same reason as for Kivy, I've backported the patch to sat_tmp to be able to use SàT and SàT PubSub with Python 3.8.

Now I'm working on infinite scroll on Cagou. It is functional but not yet smooth.

That's all for this progress note, as usual feedbacks are welcome.