A blast from the past: in early 2014, we enabled Generational Garbage Collection (GGC) for Firefox desktop. But this blog post is not about GGC. It is about my victory dance when we finally pushed to button to let it go live on desktop firefox. Please click on that link; it is, after all, what this blog post is about.

Old-timers will recognize the old TBPL interface, since replaced with TreeHerder. I grabbed a snapshot of the page after I pushed GGC live (yes, green pushes really used to be that green!), then hacked it up a bit to implement the letter fly-in. And that fly-in is what I’d like to talk about now.

At the time I wrote it, I barely knew Javascript, and I knew even less CSS. But that was a long time ago.

Today… er, well, today I don’t know any more of either of those than I did back then.

Which is ok, since my whole goal here is to ask: what is the right way to implement that page? And specifically, would it be possible to do without any JS? Or perhaps minimal JS, just some glue between CSS animations or something?

To be specific: I am very particular about the animation I want. After the letters are done flying in, I want them to cycle through in the way shown. For example, they should be rotating around in the “O”. In general, they’re just repeatedly walking a path that is possibly discontinuous (as with any letter other than “O”). We’ll call this the marquee pattern.

Then when flying in, I want them to go to their appropriate positions within the marquee pattern. I don’t want them to fly to a starting position and only start moving in the marquee pattern once they get there. Oh noes, no no no. That would introduce a visible discontinuity. Plus which, the letters that started out close to their final position would move very slowly at first, then jerk into faster motion when the marquee began. We couldn’t have that now, could we?

I knew about CSS animations at the time I wrote this. But I couldn’t (and still can’t) see how to make use of them, at least without doing something crazy like redefining the animation every frame from JS. And in that case, why use CSS at all?

CSS can animate a smooth path between fixed points. So if I relaxed the constraint above (about the fly-in blending smoothly into the marquee pattern), I could pretty easily set up an animation to fly to the final position, then switch to a marquee animation. But how can you get the full effect? I speculated about some trick involving animating invisible elements with one animation, then having another animation to fly-in from each element’s original location to the corresponding invisible element’s marquee location, but I don’t know if that’s even possible.

You can look at the source code of the page. It’s a complete mess, combining as it does a cut and paste of the TBPL interface, plus all of jquery crammed in, and then finally my hacky code at the end of the file. Note that this was not easy code for me to write, and I did it when I got the idea at around 10pm during a JS work week, and it took me until about 4am. So don’t expect much in the way of comments or sanity or whatnot. In fact, the only comment that isn’t commenting out code appears to be the text “????!”.

The green letters have the CSS class “success”. There are lots of hardcoded coordinates, generated by hand-drawing the text in the Gimp and manually writing down the relevant coordinates. But my code doesn’t matter; the point is that there’s some messy Javascript called every frame to calculate the desired position of every one of those letters. Surely there’s a better way? (I should note that the animation is way smoother in today’s Nightly than it was back then. Progress!)

Anyway, the exact question is: how would someone implement this effect if they actually knew what they were doing?

I’ll take my answer off the air. In the comments, to be precise. Thank you in advance.

Tags: mozilla, planet