Meshes and IK constraints deforming setup pose

iamymai

As I've been doing a deep dive into more complex animation over the last few weeks I've noticed that binding meshes to bones and adding IK constraints can lead to unwanted deformation in the setup pose. The mesh might shift position slightly, or more frustratingly deform to a point where I have to readjust the UVs manually. If the latter happens I can go into edit the mesh and uncheck deformed to reference what the base position should be, but it's an annoying and inefficient process. I find this is the biggest issue when I'm binding bones that include those "outside" the asset (i.e. the highest arm and leg bones in addition to spinal bones for a torso) and this leads to sloppy auto weight calculation. Oftentimes as I'm manually adjusting weights I can see the UV change position in real time.

Then when I add IK contstraints on something like a leg and foot, the position of the foot shifts a little, causing slight deformation, and I have to translate the targets in order to preserve the setup pose.

Is there a way to avoid this? Is there something I'm missing?

Nate

What exactly are you doing when you see the foot move, deforming your mesh?

You could place the target bone at the exact tip of the child IK bone by typing the position. Then when you add an IK constraint, the parent and child bones should not rotate.

You could setup your IK before binding meshes to the bones. This is probably the best solution.

iamymai

I've attached an image that shows what happens as I add the IK constraints. It's subtle, but you can see the foot's position change with each addition. At this point the mesh is bound to the bones. I'm not clear how I can determine the coordinates of the bone tip, but if I unbind the mesh, move the foot's slot outside of the bones I'm creating targets for, and then drop it back into the correct bone I avoid the position changes. It therefore looks like I need to set up IK constraints before even associating slots and bones.

There's still the larger issue of binding meshes and adjusting weights leading to unwanted deformations. I'm unable to replicate it now though, so maybe I can chalk it up to a strange bug that's fixed by restarting the program. Regardless, I've also attached an image that shows an upper arm mesh with deformation turned off, and you can clearly see the UVs on the bottom right shifting around. I never manipulated those UVs outside of Edit Mesh.

Nate

If you are creating the IK target by clicking, then it's expected your clicking won't be perfectly accurate and likely your IK bones will rotate slightly to point at the target. To position the target bone at the tip of the IK bone, parent it to the IK bone then set the local translation of the target bone to x,0 where x is the length of the IK bone. Then you would reparent the target bone where you want it and create the IK constraint.

I suggest creating bones and constraints before meshes, since seeing the bones will help you create mesh vertices where the joints are. Then do weights last, so you won't be moving your setup pose bones around after you've done weights.

Not sure what is going on your second image. If you adjust UVs in Edit Mesh mode without Deformed checked, then the image outside of edit mode will be stretched because you have changed the UVs without changing the vertices. If you don't like this, you can exit Edit Mesh mode, then click Reset on the mesh to make the vertices match the UVs. If Deformed is checked then you are changing both the vertices and UVs.