Animating SVGs from Sketch with anime.js

Animating SVGs is great, it makes posts more lively.

Animating SVGs, at least in the pipeline I’m using (Sketch and anime.js), is also stupidly difficult for obscure reasons. I am going to try to document and improve my process.[1]

Contents

  1. Exporting from Sketch
  2. Embedding SVG files
  3. Animating with anime.js

Exporting from Sketch

Permalink to “Exporting from Sketch”

There are two main problems.

1. Mitigating transforms

Permalink to “1. Mitigating transforms”

Many SVG elements are positioned using transform attributes.

As far as I can tell, the animation library (anime.js) cannot apply relative mutations to the transform attribute of SVGs. In plain language, this means you can’t move stuff around. That’s a big problem because moving stuff around is kind of the essence of animating.

To make this work, you need to be able to produce SVG elements without any transform attribute. That way, anime.js can apply absolute changes via the transform attribute.

There are good things about Sketch’s SVG export. For example, if you name layers, it keeps these names as SVG id attributes in the export. This lets you select them with your animation library and move them. Yay.

Update 10/18/21: This appears to be gone or broken now, too. The latest SVG I exported from Sketch didn’t output any ids for groups I named.

The bad thing about Sketch’s SVG export is that you lack control over how things get exported. So there are transforms on all sorts of stuff, making a bunch of stuff unusable for animation.

The good news is that Sketch supports plugins, and there is an SVG plugin that claims to give you control over these issues with features like:

  • moveGroupAttrsToElems — “Moves group attrs to the content elements.”
  • convertPathData — “Optimizes path data: writes in shorter form, applies transformations.”

The bad news is, while the plugin appears to do some things, neither of those features actually work. After applying moveGroupAttrsToElems, all groups (<g>) still have transform (and many other) attributes on them. Similarly, after applying convertPathData, some paths (<path>) still have transform attributes on them.

I opened an issue for the first problem, but as there are unresolved issues on that repository that are five years old—including a very similar report to my own that’s been closed and still broken for three years—I am not optimistic.[2]

My current workaround is: because, after running the plugin, most groups have transforms on them, but most children (like paths) contained in the groups don’t, I use anime.js to select all children of a group, using a selector like #group-id *. Then, I add transform animations to the children directly, which give them relative motion.

2. Converting text to shapes

Permalink to “2. Converting text to shapes”

Not everyone has the same fonts installed. Text in SVG, by default, simply contains the font that’s supposed to be used, and the text to render. If someone doesn’t have the font you want installed, text will not display properly.

Sketch has a way to convert text to outlines. This is a destructive process; once you do it, you can no longer edit the text or any of its properties (like typeface, size, weight). Obviously, this makes iterating unpleasant.

Sketch lacks any SVG export option to automatically convert text to shapes. This is a bummer. (It was suggested three years ago into the pointless void of product forums.)

One workaround I’ve seen is to “intersect” all text with a box of the same color as the text. As far as I can tell, this must be done separately per text color, and text must either be grouped first (or each text won’t mutually intersect and become blank) or intersected with a separate box. Doing this makes the text export as paths, but can still be edited by selecting the layer.

Unfortunately, the workaround, at least as I’ve implemented it, is not only tedious, but pollutes the sketch with these background objects that make selecting both the text and other content quite difficult.

My current workaround is: to wait until my final draft, and convert all text to outlines then. I am also trying to start keeping little samples of non-converted text around outside the arboard area so that I know what it was in case I need to make more edits down the road.

Embedding SVG files

Permalink to “Embedding SVG files”

As far as I can tell, you cannot animate an SVG file with anime.js if it’s not literally dumped inside the source HTML page. This was the approach I took for the diagrams I’d made so far. Today, I finally went down the full rabbit hole to solve this issue.

You cannot do <img src="picture.svg" />. The image will be rendered, but the DOM won’t have all the SVG nodes, so they can’t be selected by the animation library. This one is obvious.

You can do <object data="picture.svg"></object>, but it requires two workarounds.[3]

The crux of the issue is that contents of the SVG will be inserted, but anime.js won’t be able to find the SVG nodes with its element selectors. This is because the SVG is actually inside a new document within the <object> node.

The first workaround you must do is to get the document inside the <object> element, and explicitly query your nodes.

For example, if we have the object

<object id="my-diagram" type="image/svg+xml" data="picture.svg"></object>

… then we can get the document that gets loaded inside it with

document.getElementById('my-diagram').contentDocument

However, if you do this immediately, or even after the DOMContentLoaded event fires, you will be successfully given an empty document. Bummer. The contents haven’t loaded yet.

So, instead, you can wait for it to load (thanks, as usual, to a StackOverflow answer):

document.getElementById('my-diagram').addEventListener("load", function() {
const innerDoc = document.getElementById('my-diagram').contentDocument;
};

I probably could have shortened this by relearning how this works.

Then, using that innerDoc, you can write your own query selector to send to anime.js:

// continuing the above, inside the anonymous function
anime({
targets: innerDoc.querySelectorAll("#fun-group *"),
translateX: 10,
...
});

This still doesn’t work. This is quite bizarre, because you can verify with Chrome’s developer tools that innerDoc.querySelectorAll("#fun-group *") does return a NodeList (well, if you have matching stuff in your SVG). And, if you run the same thing on an <svg> directly inside the page, it works.

And, so we are on to our second quandary: how to tell anime.js about these foreign document nodes we’ve been able to successfully query?

First, we enter a debugging process you can skip over.

Aside: Debugging anime.js

  • the targets appear saved correctly (as animatables), but the list of animations is empty (in createNewInstance())
  • getAnimationType() matches no if statement (and so returns undefined)
    • however, el is a NodeList, but it looks like the code is expecting it to be a single element
    • this makes me think that maybe the code that array-ifies the passed values is broken; the NodeList is passing its checks, but it shouldn’t be, because it’s not being unpacked correctly for later.
  • toArray() checks o instanceof NodeList, which fails, even though Chrome’s debugger says its a NodeList. So I wonder if the issue is that it’s a “foreign” NodeList because it’s from a different DOM? Anyway, when this check fails, toArray() returns [o], which means we now have [NodeList]—in other words, an array of length 1 containing a NodeList. That seems to be wrong.
  • oooh, I totally mised it then—animatables above in createNewInstance() was actually an [NodeList] (array with the NodeList as a single element). Or maybe I saw this and assumed it was OK because animatables is plural and I thought maybe there could have been multiple selectors? Either way.
  • I think the root of this might be the o instanceof NodeList check. I might try to experiment with this using the raw selection.
  • Yeah, right when I get the elements, els instanceof NodeList fails. I suspect fundamentally solving this might require next-level DOM wizardry. Instead, the workaround in the issue I came across works: sending in the NodeList by spreading it first with [...els].

The tl;dr: is that anime.js has a bug where it can’t identify the foreign NodeList as a NodeList, so it wraps it in an array, which screws up the later steps, so no animations end up being made.

Enter the second workaround, given by the GitHub issue that sent me further down this hole: repackaging the NodeList as an array, simply by spreading it out.

In other words:

const nodeList = innerDoc.querySelectorAll("#fun-group *");
anime({
// targets: nodeList, // this is what we were doing
targets: [...nodeList], // this is what works
translateX: 10,
...
});

Putting this all together:

// IDK whether this outer event listener is necessary, but I don't think
// it can hurt (famous last words).
document.addEventListener('DOMContentLoaded', function () {
// Wait for the SVG contents to load
document.getElementById('my-diagram').addEventListener("load", function() {
// Grab the inner document
const innerDoc = document.getElementById('my-diagram').contentDocument;
anime({
// Query the inner doc for the nodes, and repackage them
// as a vanilla array.
targets: [...innerDoc.querySelectorAll("#fun-group *")],
translateX: 10,
...
});
});
});

In summary, my current workarounds are: (1) wait for the <object> to load and get the nodes we want to animate ourselves, (2) unpack them to a vanilla array before sending into anime.js.

Animating with anime.js

Permalink to “Animating with anime.js”

I’ve run into two main issues.

1. Cannot apply relative changes to transforms

Permalink to “1. Cannot apply relative changes to transforms”

As I mentioned above to motivate trying to clean up Sketch’s SVG exports, I do not think anime.js can apply relative changes to transform attributes.

anime.js can:

  1. Apply relative changes to scalars using strings like +=10, -=10, and *=10.

  2. Apply full overwrites of SVG transform attributes by:

    1. Overwriting the transform attribute directly by mutating its values

    2. Implicitly overwriting the transform attribute by adding a style="transform: translateX(...) translateY(...);". This will then be applied instead of the transform attribute (rather than composing them).

Unfortunately, I don’t think there is a way of combining points 1 and 2: using relative changes to mutate transform values.

My current workaround is: to attempt to avoid this by trying to get SVG to output things that I want to animate that don’t have transform attributes at all. That way I can use point 2 above to apply fresh transforms to move them relative to where they start.

2. Cannot easily compose motion

Permalink to “2. Cannot easily compose motion”

This may be a limitation of my own understanding. The main feature presented by anime.js for complex motion is a timeline. This works for sequential motion. But I do not know how to accomplish concurrent motion.

By concurrent motion, I simply mean: imagine that you want a circle to do two things at the same time:

  1. bob up and down
  2. travel around the page

This motion should be compositional: the circle travels around, bobbing up and down all the while.

I do not know how to easily accomplish this with anime.js.

My current workaround is: to avoid using compositional motion.

Other little bugs

Permalink to “Other little bugs”

Just keeping a note here in case they’re note part of the above (though I’m not sure).

  • SVG rotations (can’t easily pick a center point)
  • SVG translateX/Y on Safari

  1. This is one of those notes that will probably be relevant to a maximum of three other people, ever, on planet earth. But if any one of those people is just starting down this path and running into these problems, I hope this saves you a massive amount of the confusion that I slogged through. ↩︎

  2. For those wondering about the failings of open source, this is it: software that nearly works but has fallen out of maintenance.) ↩︎

  3. As an aside, I don’t understand how these problems aren’t trivially solved. Why is what I’m doing a corner case? I would think that if you wanted to make animations online, the simplest content to use would be SVG. Rather than positioning everything by hand with HTML <div>s or something, you can use graphical software to draw diagrams and export them as SVG. Plus, SVG is native browser tech, and it’s vectorized so it renders nicely at different scales. Sketch is super mainstream vector software. As far as I can tell, besides a couple CSS libraries with gaudy effects, anime.js is a mainstream animation library. I’m not even tied to Sketch or anime.js, they just seem like obvious default choices for “how to make a simple animation on your website.” So, why is getting the pipeline working so hard?!? ↩︎

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started 31 Jul 2021
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