FBX Shape Key In-Between – Create & Export In-Between Shapes in Blender

“I wish Blender could create in-between shapes and export them to FBX…”

I’ve been saying this on my blog and on X for a while now… and I finally went ahead and made it myself !

Introducing the Blender add-on “FBX Shape Key In-Between” !!

 

 

I’ve also published the add-on’s manual on GitHub, but in this article I’ll go into a bit more detail on how to use it, with some practical examples along the way.

If you’re developing games with Blender + Unity, I think being able to create in-between shapes and export them to FBX directly in Blender is a feature you’ve been waiting for! Definitely check it out~

 

What is the Blender Add-on: FBX Shape Key In-Between?

FBX Shape Key In-Between is an add-on that lets you create in-between shapes in Blender and export them directly to FBX.

You can create and preview in-between targets for shape keys, then export them to FBX in a format compatible with Autodesk Maya.

 

What’s so good about being able to create in-between shapes?

Say you’re making a closed-eye expression for a 3D character model. You can create a “half-closed eyes” shape and set it up as an in-between shape. That way, the eyes pass through exactly the half-closed shape you drew in your concept art, and the mesh keeps a clean silhouette all the way through the deformation — no polygons clipping into each other partway.

It’s not just for faces, either. For simple object animation, creating several in-between shapes lets you animate with nothing but a shape key slider — no bones, no weight painting.

That’s the great thing about in-between shapes: what you can do with them really comes down to your own ideas!

 

 

What You Can Do

FBX Shape Key In-Between mainly lets you do two things:

1. Create in-between shapes

By creating a shape key named “Shape Key Name@Value” for a normal shape key you’ve made in Blender, that shape key gets set as an “in-between shape,” enabling deformation through the in-between shape.

Pressing the Setup Preview Drivers button in the FBX Shape Key In-Between add-on panel lets you preview the motion via the in-between shape by moving the “Shape Key Name” slider.

If you rename or delete the “Shape Key Name@Value” shape key and press Setup Preview Drivers again, the preview updates to show the motion without going through the in-between shape key.

 

2. Export them to FBX

Exporting FBX with Blender’s Built-in Feature

From the Blender menu, select File → Export → FBX (.fbx) to export. Shape keys named “Shape Key Name@Value” are automatically merged as in-between shapes of “Shape Key Name” and exported into the FBX.

 

Exporting FBX with Third-Party Add-ons

When exporting to FBX using third-party add-ons such as BetterFBX, in-between shapes are not merged automatically.

Running FBX In-Between Merge from FBX Shape Key In-Between on the exported FBX file merges shape keys named “Shape Key Name@Value” into “Shape Key Name” as in-between shapes.

The original FBX file, before the in-between shapes are merged, is renamed with a .bak extension and kept as a backup

 

 

 

Trying It Out

FBX Shape Key In-Between is simple to use — there are only three buttons:

The key point when using it is this:
always press Setup Preview Drivers after creating or renaming an in-between shape!

 

When merging in-between shapes into an exported FBX, the merge process looks at the “Shape Key Name@Value” naming. Blender’s in-between shape preview also relies on the same naming, but the preview doesn’t update automatically.

So if you don’t press Setup Preview Drivers, the motion you see in Blender’s preview via the in-between shape can end up different from the motion actually produced via the in-between shape in the exported FBX — so be careful.

It’s fine to press Setup Preview Drivers as many times as you like, so don’t hesitate to use it~

 

Also, in FBX Shape Key In-Between, creating a shape key named “Shape Key Name@Value” is what sets up an in-between shape (equivalent to what Maya calls an In-Between target).

As long as you don’t create a “Shape Key Name@Value” shape key, it works exactly like creating a normal shape key.

There are several ways to create an in-between shape, so I’ll walk through them one by one as we actually create some.

 

・Creating an In-Between Shape Directly

Press the Add In-Between Key button to create a shape key named “Shape Key Name@Value”.

If you press Add In-Between Key while dragging the slider of the “controller shape key” (the one without @), you can create an in-between shape from a mid-way point of the deformation.

Once you’ve created @-suffixed in-between shape keys, it’s recommended to sort them in numerical order for easier viewing.

 

You can also press Add In-Between Key without moving the controller shape key’s slider, and instead type in the timing where you want to insert the in-between shape before creating the new in-between key.

 

For the number after @, you can use either a range of “0.1 to 1.0” or “0 to 100“.

When you add an in-between shape with Add In-Between Key while other in-between shapes already exist, the notation of the number after @ is automatically matched to be consistent with the existing ones.

 

 

・Setting an Already-Created Mesh as an In-Between Shape

Instead of adding a shape key directly on the base mesh, you can also load a separately-created, already-deformed mesh as a shape key.

If you’re used to creating blend shapes in Maya, this method will probably feel more familiar.

A common approach for characters is to separate out just the face mesh, then create and arrange deformation target meshes for facial expressions side by side. As long as the expression meshes have the same vertex count and local axes as the base, this method works fine too.

If you also want to set up in-between shapes using FBX Shape Key In-Between, name the mesh in the format “Shape Key Name@Value”. Also create the final deformation as “Shape Key Name@1.0”.

After this, select in the order “all @-named meshes → the base mesh you want to deform”, then from the Shape Key dropdown menu (▽), choose New from Objects (or Join as Shapes in Blender 4.2).

Once the @-suffixed shape keys are registered, press Setup Preview Drivers in FBX Shape Key In-Between. This creates the controller shape key without @, so all you need to do afterward is move that one.

 

 

 

・Animating a Shape Key

When you want to animate a shape key that goes through an in-between shape, add animation keyframes on the “controller shape key”—the one named without @.

The controller shape key is meant for previewing deformation and creating animation, so please avoid editing this shape key’s vertices directly.

Note that the @-suffixed in-between shape keys are controlled by drivers, so you cannot add animation keyframes to them.

 

・Exporting the Animation to FBX and Checking in Unity

Let’s export the animation that goes through the in-between shape to FBX and check it in Unity.

However, keyframing only the shape key isn’t enough to get it exported to FBX. To export to FBX, you also need to keyframe the armature and export the two together.

So let’s also add keyframes to the armature and animate the whole thing.

Here’s the result of exporting this to FBX and playing back the animation in Unity.

It’s the same as the animation we saw in Blender! Hitomi-san blinks cleanly here too.

By the way, here’s what it looks like when importing the same FBX into Maya.

Opening the Shape Editor shows that the in-between shapes (In-Between targets) are properly set up. (The slightly odd object naming that happens when bringing things from Blender to Maya is just a minor quirk you’ll have to live with.)

That wraps up the usage guide for FBX Shape Key In-Between~

 

Installation

FBX Shape Key In-Between is sold on BOOTH and Gumroad.

The purchased package is a single ZIP containing two ZIP files.

 

・Using the Installer (Recommended)

If your Blender has internet access, installing via the installer is recommended.

Note: If Blender is set to offline mode, you’ll need to allow online access.

When you install the add-on via the installer, new versions of FBX Shape Key In-Between will show up under the Extensions update list, so you can update with a single click.

 

・Direct Installation

If you’re using Blender offline, installing via the installer isn’t possible. Instead, you can install directly from the add-on’s zip file.

If you install directly from the add-on zip, new versions of FBX Shape Key In-Between will not show up under the Extensions update list, even when they’re released. You’ll need to manually replace it with the new version yourself.

 

License

FBX Shape Key In-Between is licensed under the GNU GPL v2 or later. See the LICENSE file for details.

 

Notes

 

Summary: Please Consider Getting FBX Shape Key In-Between!

FBX Shape Key In-Between is an add-on that lets you create in-between shapes in Blender and export them to FBX.

Now that you know what it can do and how to use it, I hope you’ll give it a try~

FBX Shape Key In-Between is sold on BOOTH and Gumroad.

 

To responsibly continue ongoing maintenance—supporting Blender updates and handling user inquiries—this add-on is priced at ¥1,500 (about $10).

I’d be delighted if you took this opportunity to pick it up.

 

Being able to create in-between shapes in Blender and export them to FBX is something I’d wanted to do for a long time.

Since I make indie games myself with Blender + Unity, I think this add-on has turned out to be quite practical.

I’m always happy to receive questions or bug reports about this add-on.
Feel free to reach out either through the comments on this article or via the contact form.