Some tips for painting skin weights in Maya

So, painting skin weights. It is a major part of our rigging lives and sadly one of the few bits, together with joint positioning, that we cannot yet automate, though in the long run machine learning will probably get us 99% there. Untill then though, I thought I would share some of my tips for painting skin weights with maya’s native tools, since whenever I would learn one of these I felt stupid for not finding it out earlier as, more often than not, it was just so simple.

I am sure a lot of you are familiar with these, but even if you learn just a single new idea about them today, it might boost your workflow quite a bit. Additionally, I know that a lot of you are probably using ngSkinTools and literally everyone I know who works with it says they cannot imagine going back. So I am sure that some of the things I am going to mention are probably already taken care of ngSkinTools, but if you, like me, have not had the chance to adopt it yet, you might find these helpful.

I am going to list these in no particular order, but here is a table of contents.

Contents

  1. Simplifying geometries with thickness and copying the weights
  2. Using simple proxy geometry to achieve very smooth weights interpolation quickly
  3. Duplicate the geometry to get maya default bind on different parts
  4. Copy and paste vertex weights
  5. Use Post as normalization method when smoothing
  6. Move skinned joints tool
  7. Reveal selected joint in the influence list
  8. Some handy hotkeys
  9. Average weights
  10. Copy and paste multiple vertex weights with search and replace
  11. Print weights

So with that out of the way, let us get on with it.

Simplifying geometries with thickness and copying the weights

This one comes in very handy when we are dealing with complex double-sided geometries (ones that have thickness). The issue with them is that when you are painting one side, the other one is left unaffected, so as soon as an influence object transforms the two sides intersect like crazy. That is often the case with clothes and wearables in general.

The really easy way to get around this is to
1. Make a copy of the geometry
2. Remove the thickness from it (when having a good topology it is as simple as selecting the row of faces which creates the thickness and deleting it together with one side of the geo)
3. Paint the weights on that one
4. Copy the weights back to the original geometry

Painting skin weights tips - Using a one sided proxy geometry when working with thickness

Now, a really cool thing that I had not thought of untill recently is that even if I have started painting some weights on the double sided geometry to begin with I can also maintain them, by copying the weights from the original one to the simplified one before painting it, so I have a working base.

That means, that if I have managed to paint some weights on a double sided geometry that kind of work, but the two sides are not behaving 1 to 1, I can create a simplified geo, copy the weights from the original one to the simplified and then copy them back to get the 1 to 1 behaviour I am looking for.

Using simple proxy geometry to achieve very smooth weights interpolation quickly

This one is very similar to the first one, but I use it all the time and not only on double-sided geometries.

Very often there are geometries that have some sort of a detail modeled in them that make it hard for weight painting smooth weights around it.

Consider the following example. Let us suppose that we need this geometry to be able to stretch smoothly when using the .translateX of the end joint.

Tips for painting skin weights in maya - Using a simple geometry to copy weights to models which are hard to smooth weights for.

Doesn’t look great with default skinning, but also if I try to block in some weights and smooth them, it is likely that maya won’t be able to interpolate them nicely. To go around it, I’d create a simple plane with no subdivisions so I can have a very nice smooth interpolation from one edge to the other.

Tips for painting skin weights - Using a simple plane without subdivisions to achieve a smooth weights interpolation for copying to complex geometries.

Copying this back to the initial geometry gives us this.

Tips for painting skin weights - Smooth skinned complex geometry using weights from a simple plane.

Very handy for mechanical bits that have some detail in them and also need to be stretched (happens very often in cartoon animation).

Duplicate the geometry to get maya default bind on different parts

So, very often I have to paint the weights on a part of a geometry to a bunch of new joints while I still need to maintain the existing weights on the rest of it. More often than not, I would be satisfied with maya’s default weights after a bind, but obviously if I do that it will obliterate my existing weights.

What I do in such cases is make a copy of the geometry and smooth bind it to only the new joints. Then I select the vertices on the original geometry that comprise the part I want the new influences in and I use the Copy skin weights from the duplicated one to the selected vertices. If the part is actually separated from the rest of the geometry that should do it, but if it s a more of an organic shape, there is going to be some blending of the new weights with the ones surrounding them.

I could imagine, though, that having the ability to have layers and masks on your skin weights would make this one trivial.

Copy and paste vertex weights

I am guilty of writing my own version of this tool just out of the ignorance of not knowing that this exists. Basically what you can do is select a vertex, use the Copy vertex weights then select another one (or more than one) and use the Paste vertex weights command to paste them. Works cross-geometries as well.

A cool thing about the tool that I wrote to do this is I added a search and replace feature that would apply the weights to the renamed joints. For example if I am copying a vert from the left arm and I want to paste it on the right I would add “L_” to “R_” to my replacement flags.

Use Post as normalization method when smoothing

So, I have met both people who love and who hate post. I think the main reason people dislike it is because they don’t feel comfortable with their weights being able to go above 1.0, but I have to say that sometimes it is very handy. Especially for smoothing. Everyone knows how unpredictable maya’s interactive smoothing is, and that’s understandable since in a lot of cases it is not immediately obvious where should the remaining weights go to.

Smoothing on post is 100% predictable which I think is the big benefit. The way it works is that it smooths out a joint’s influence by itself, without touching any of the other weights. That means that the weights are not normalized to 1.0, but instead of verts shooting off in oblivion post normalizes them for our preview. That is also why it is not recommended to leave skinClusters on Post as the weights are going to be normalized on deformation time which would be slower.

So more often than not my workflow for painting weights would be to block in some harsh rigid weights, then switch to Post and go through the influences one by one flooding them with the Smooth paint operation once or twice.

Move skinned joints tool

I am not sure which version of maya did this tool come in, but I learned of it very recently. Essentially you can select a piece of geo (or a joint) and run the Move skinned joints tool, then you can transform the joint however you like or you can also change the inputs going into it without affecting the geometry, though, you’d have to be careful to not change the tool or the selection as that would go out of the Move skinned joints tool. Ideally any other changes than just moving/rotating them about should be ready to be ran in the script editor.

I would not recommend using this for anything else than just testing out different pivot points. Doing it for actual positioning in the final skinCluster feels dirty to me.

Reveal selected joint in the Paint skin weights tool influence list

Only recently I found out what this button does.

Paint skin weights tool - reveal selected joint in influence list

It scrolls the list of influences to reveal the joint that we have selected, which is absolutely brilliant! Previously, I hated how when I need to get out of the Paint skin weights tool and then get back inside of it, the treeView is always scrolled to the top of the list. Considering that the last selection is maintained, pressing that button will always get you back to where you left off. Even better, echoing all commands gives us the following line of MEL that we can bind to a hotkey.

artSkinRevealSelected artAttrSkinPaintCtx;

Some handy hotkeys

I have learned about some of these way too late, which is a shame, but since then I’ve been using them constantly and the speed increase is immense. I hate navigating my mouse to the tool options just to change a setting or value.

  • CTRL + ALT + C – Copy vertex weights
  • CTRL + ALT + V – Paste vertex weights
  • N + LMB (drag) – Adjust the value you are painting with
  • U + LMB – Marking menu to change the current paint operation (Replace, Add, etc.)
  • ALT + F – Flood surfaces with current values

For more of these head on to the Hotkey editor, then in the Edit hotkeys for combobox go for Other items and open up the Artisan dropdown.

From here on I have added some of the functionalities that I have written for myself, but sadly the code is very messy to be shared. Luckily, it is not hard at all to write your own (and it will probably be much better than mine), but if you are interested, do let me know and I can clean it up and share it at some point.

Average weights

This one I use a lot. What it does is, it goes through a selection of verts and calculates the average weights for all influences and then goes through the selection once more and applies that average calculated weight. Essentially, what this results in is a rigidly transforming collection of verts. Stupidly simple, but very useful when rigging mechanical bits, which should not deform. Also I have used it in the past on different types of tubings and ropes where there are bits (rings, leafs, etc.) that need to follow the main deformation but not deform themselves.

Copy and paste multiple vertex weights with search and replace

In addition to the above mentioned copy and paste vertex weights, I have written a simple function that copies a bunch of vertex weights and then pastes them to the same vertex IDs on a new mesh. It is not very often that we have geometries that are copies of each other, but if we do this tool saves me a lot of time, because I can then just skin one of them, copy the weights for all verts and then paste them to the other geometry using the Search and Replace to adjust for the new influences.

Comes in particularly handy for radially positioned geometries where mirroring will not help us a lot.

Print weights

Quite often I’d like to debug why something is deforming incorrectly, but scrolling through the different influences can get tedious especially if you have a lot of them. So I wrote a small function that finds the weights on the selected vertex and prints them to me.

This is the kind of output I get from it.

#####################################
joint2 : 0.635011218122
joint1 : 0.364988781878
#####################################

As I said, there is a lot of room for improvement. It works only on a single vert at the moment, but I could imagine it being really cool to see multiple ones in a printed table similar to what you would get in the component editor.

What would be even cooler would to use PySide to print them next to your mouse pointer.

Conclusion

Considering that we spend such a big chunk of our time on painting weights we should do our best to be as efficient and effective as possible. That is the reason I wanted to share these, as they have helped me improve my workflow immensely and I hope you would find some value in them as well.

2 Comments on "Some tips for painting skin weights in Maya"


  1. Print weights:
    Also a easy way to see this is the compononent editor, which shows you this information in the smooth skinning tab. It can also be used to change the skinning values on the selected vertexes in a numerical way…

    Reply

    1. Yes, that’s totally fair, I just really prefer working with as little editors opened as possible. Since I always have the script editor opened, it is really easy for me to just print the weights and see them there. If I have to open the component editor, then I also need to close it and it seems like a bit too much hassle for just checking the current weights.

      I could definitely imagine, though, that being used to using the component editor the printing of weights would seem totally unnecessary.

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *