Mirror modifier and shape keys?

Deformation bones just aren’t cutting it for some of the movements I need, so I figure I’ll need to make some shape keys. The only problem is that, if I need to change the mesh later, I’d rather not have to apply the mirror modifier to it but I need shape keys that are specific to one side. Is it possible to have a shape key only influence one half of the mesh if there’s a mirror modifier in place already? Like .L or .R shape key in the same way that there can be .L and .R vertex groups without applying a modifier?

I i remember correctly this is possible :
you can have a shape like smile, that you can have only on the left side by using a vertex group.
then you dupicate that shape or do new shape from mix and make the right side

I don’t see a way to do this, to have shape keys that only affect half of a mesh when the mesh has a mirror modifier on it. Shape keys deform the mesh before any modifiers work on the mesh. If you need different left/right shape keys, you have to apply the mirror modifier.

Still trying to figure out why you need L & R shape keys for a mesh with a mirror modifier on it… :exploding_head:


That’s one of the reasons i am avoiding using shapekeys. Too much restrictions linked to mesh. You can’t apply modifiers on mesh containing shapekeys, also you can’t edit topology.

I was hoping to use them to simulate muscle deformations and similar things that are very difficult to make look good by using bones. Facial expressions make sense to be mirrored, but the rest of it doesn’t. Thanks.

Right. I totally believe that good topology and careful weight painting will get you to a 90% perfect deforming mesh. To get that last 10%, you need to use tricks like shape keys. By the time you are at this stage of creating a character, I would assume the mesh topology is as good as it’s going get. No further editing of the mesh will help, so apply the mirror modifier, then fix the last 10% of deformation problems with shape keys.

I think it is just the opposite.

First, using a shape key to make a bicep muscle bulge when an arm is flexed is a good use for a shape key. But wouldn’t the left arm’s and right arm’s bicep muscle bulge about the same amount?

Using mirrored facial expressions don’t make sense to me. Many facial expressions can be one sided, like a raised eyebrow, or the corner of a mouth. So you would need separate L/R shape keys here.

Again, by the time you are thinking about shape keys, the mesh should be finalized. Then apply the mirror modifier and work on L/R shape keys.

Just my 2 pennies…


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They would but not at the same time unless both arms are flexed equally and as far as I’ve been able to tell, activating the key on one side must also activate it on the other if it’s a single, symmetrical key.

Try to use bendy bones to simulate bicep\tricep muscles. I found it very usefull. Just make usual 3 bone chain , middle bone is “muscle”, first bone is ‘head’, last one “tail”, ‘muscle’ bone is child of ‘head’ bone, muscle bone constrained to ‘tail’ bone with stretch to constraint. “Head” bone should be placed lower than elbow at lower arm bone, ‘tail’ bone at top of shoulder, so your ‘muscle’ bone goes along shoulder down to lower arm. Next you parent head ‘bone’ to lower arm and ‘tail’ bone to shoulder so your ‘muscle’ will be shirinking\stretching when lower arm will be rotating. You can set amount of stretching in bone constraint options. This way you can get nice muscle deformations even for face. Shapekeys are usefull to simulate lesser deformations like skin ‘wrinkles’, but it should be done after finalizing your character mesh at later stages.

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Here is good tutorial how to use bendy bones to simulate muscle deformation. Very flexible method in my eyes:

Thank you. And it shouldn’t matter if there are two bones for each arm segment to smooth out deformations?

It doesn’t matter how much there are bones for each segment you may have as much as you need, only thing you should care is proper parenting so your segments should move right way to give you right deformations. Personnaly i found for myself that two muscle bones are enough for each arm segments (shoulder and lower arm). For shoulder f.e. it’s tricep and bicep muscles. You add these bone chains, and carefully weight paint muscles bones. More weight you assign for muscles more deformation effect they cause. You can make this system even more flexible: You parent ‘head’ bones not to lower arm directly, but to the copy of lower arm bone (i call it rotation helper). Just copy arm bone, parent it to shoulder, add copy rotation constraint with lower arm as target and set influence about 0.5 (you may tweak influence value to get result you like). This will give you more flexibility. If you know human anatomy well enough, you can get realistic muscle deformations for free - bendy bones will do it for you, and you can reuse this system for any characters with different topology, this is really usefull. You can see closely at such system in Manuel Bastiony LAB addon, it has muscle rig with similar aproach. It has advanced muscle system close to real human anatomy. You can build simplified system and still get really pleasant effect. You need just to get how it’s work - it’s pretty simple but really effective.

More of that - using muscle system allows you to get dynamic muscles deformations without much efforts, you can use jiggle bone addon to add physic simulations for your muscles, so when you animate your character muscles will deform as real muscles\tissue. You will need just tweak few parameters to get good effect. Bouncing belly, buttocks, biceps, boobs and so on you will get for free.

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Anyone here have an easy way to assign custom shapes to every bone in a rig at the same time? I want to be able to work with the bendy bones in their BBone form but think it would be less of a headache to visualize all the others as being octahedrons.

This addon is quite useful when working with shape keys -

The whole shapekey workflow is quite basic in blender though, having a good system for correctives, inbetweens, updating shape keys with storing the old ones as meshes, batch exporting/importing, maintaining corrective combinations while updating hero shapes… the list’d be pretty long. I know some people (me included) who’d pay good money for a shape key management system like the ones used in feature vfx. It’s not that complex either, most of those systems are based on naming conventions, with that in mind it should just be a push of a button to tweaks/refine parts of a rig.

I apologize, I should have mentioned applying the mirror modifier before making shape keys. as mentioned here:

True, you can’t apply modifiers to a shape keyed mesh. So, when you’re done creating & fine tuning the mesh, apply the mirror modifier, then proceed with creating shape keys. At some point in time, more than likely, you’ll apply the mirror modifier. It’s no big deal to apply the mirror modifier.

I tried this approach once, and gave up on the idea. TBH, it was years ago, before the upgrade to bendy bones in blender. I don’t remember why I gave up on the idea… Maybe it was the complexity that it added in the armature vs simplicity of shape keys. True, such a system would work with multiple characters. I just wonder how well it would scale for different types of humans. Would the same armature/muscle system used in a 300 lb male football player work in a 100 lb school girl?


For fat or muscular characters you just add additional muscle bones and there you go. :slight_smile: