NHR-7 – Skinning

Content of Lesson 7:

Preparation

After all the testing needed to make sure that the skeleton reacts to our manipulations as desired, switch back to object mode. We are going to tell Blender that this skeleton needs to drive the whole horse, both object and its deformations.

Select the horse first, then SHIFT-select the skeleton, so that both are being selected at the same time.

You can initialise the basic preparation from the ToolShelf (Skining panel). There you find a few options from Avastar to proceed with parenting the mesh to the Armature. While the skinning panel can speed up the process, let’s go ahead and step through the “pure blender” process. So instead of parenting the Mesh in the skinning panel, proceed as follows…

The Weight Selection is new to Avastar-1.1

Parenting

With the current selection made (first the mesh, then SHIFT select the armature) , hit CTRL-P on the keyboard. This hotkey triggers the parenting option menu. We are especially interested in the Armature Deform section here. For our needs select the option “With Automatic Weights”.

Parenting from the Menu bar:
Object -> Parent -> Armature deform -> …
This is intended to call the selected function. But due to a bug in the Blender UI the popup box shows up instead, so you have to select your option twice.

The Armature Deform parenting does a couple of tasks in a row:

• The mesh horse object will be parented to the Armature OBJECT, meaning that in object mode the horse will keep following the Armature when it is moved in object mode.
• All vertex groups for the horse bones are created in the horse object data. There is exactly one vertex group per deform bone.
• The vertex groups contain an initial mapping between the mesh vertices and the deforming bones in the armature. The weight maps are automatic calculated to deform the mesh accordingly to the matching bones.
• A new Armature modifier is created and already set up to target Avastar’s Armature.

Note: Although Blender does a very good job here in general, this automatic weighting can contain wrong mappings. Hence this is meant to be an initial configuration for later manual improvment. The automatism can not ensure that all weights are correct and work as intended.

From now on, the horse will follow the skeleton in all the transformations we apply to it in both Object Mode and Pose Mode. But as indicated we have to carefully check if the mesh behaves correct and as intended in all places. And yes, there is a problem right now, hence…

Weight tools

Left: Original mesh. Right: Mesh deformed after parenting

When we examine the horse’s head closer we see that it appears to be crushed on the forehead. This happens because the eye bones have been automatically weighted to the head. Those bones’ vertex groups should only influence the eye meshes and nothing else. But we do not have any eyes in this horse model, we actually could delete all weights associated to the eye bones. This is the task we need to work on right now.

But we also realize that the rest of the automatic skinning already works pretty well. So we only have to fix the eyes.

Workflow Preset “Skin”

Avastar provides Presets for 3 workflows related to animation. The Preset buttons are in the Tool Shelf (Show Bones panel):

So… select the Skin Preset. When you now select one eye bone, you should see the weights represented as colors from Blue(Cold) to Red(Hot), see image.

When you select one eye bone, you see it is unintentionally skinned to the head.

When you check your model after you have called the Skin preset, the distortion seems to have disappeared. this happens because the Preset unlocks the bone rotation constraints which normally glue the SL Base Bones to the control bones. And the control bones have their own constraints which force the eyes to look at the eye target even in rest pose…

You see the rig can become rather complex. However, here is a trick how we can keep the constraints intact in Skinning mode:

In the Tool Shelf, right above the Show Bones section, we see the Bone Settings section. There we can reinforce the locking of the Rotations by clicking on the Lock button:

And now the distortions can be seen again in Weight Paint mode. If you look carefully you will see that the eye bones now are oriented differently. This is because the eyes are again constrained to follow the Eye target (currently invisible). And this causes the Distortion on the head to appear.

Note: The amount of distortion is depending on where the Eye Target is located. When you have put the eye target far away from the head, then you might not see the distortion. In that case select the eye bones and rotate them manually to see their influence on the head.Our goal will be to get rid of these distortions. So lets see what options we have…

Once we’re in weight paint mode, we can either select the bones for which we want to define the deformations. And then use paint brushes to “paint” weight data on the mesh surface. Or we can use …

The Vertex Groups Panel

When we select a bone in the 3D Viewport while in Weight Paint mode, Blender automatically selects also the vertex group corresponding to the selected bone. You find the vertex Groups panel in the Object Data properties of your mesh (the Horse). So you either can select a bone or you can select a vertex group in the list.

Pitfall Alert: When selecting a vertex Group from the list Blender does not select the associated bone. So don’t get confused…

Vertex Groups in Edit Mode

This comes in very handy now, because this selection will be kept even when we switch modes. Indeed just switch to Edit Mode (Tab key on the keyboard or use the drop down selector we used before).
And in the Properties sidebar (right sidebar) you even can turn on the display of vertex group data in edit mode. (see image)

There is one other setting that can help us a lot. Do you remember that normally any mesh changes due to Posing do not show up in Edit mode ? You can change that as well!

Pose Changes in Edit Mode

• Open the Modifier Stack
• Locate the Armature

Now Enable following options:

• Use modifier while in edit mode
• Apply modifier to editing cage during edit mode

Weight Display in Edit Mode

When you have enabled the Show weights Option and your armature is configured as described above, then your Mesh will display the current selected Vertex Group also in Edit mode (see image)

Editing Weights in Edit Mode

In Edit mode the Vertex Groups Panel now shows 4 new buttons and a slider labeled “Weight”. The Name field still shows the previously selected bone’s Vertex Group (vgroup) as the currently active for editing.

The buttons are used for:

• Assign selection to active vgroup
• Remove selection from active vgroup
• Select all vertices from active vgroup
• Deselect all vertices from active vgroup

We will now use the Vertex Groups Panel to set all weights of the Eye bone to 0.0:

• Make sure that no vertex is selected on the horse head!
• Use the Select Button in the Vertex Groups tab to select all vertices assigned to the Vertex group

Now you see a big area of vertices has been selected in the View Port. All these vertices are influenced by the Eye Bone.

This is obviously wrong, since the eye bones are meant to drive the eyes and nothing else! And since we do not even have eyes in our model (yet) we could simply remove the Vertex Groups (vgroups) for now…

So we have 3 options:

Remove the Eye Vertex Groups

Remove the vertices from the Eye bones

Assign a value of 0.0 to all vertex values of the Eye Bones

Assigning Values to Vertex Groups

So lets use the third option to set all vertices of the Eye bone vertex group to 0.0 as follows:

Now look at the head. it has turned completely blue. This is an indication for the bone having no influence on the mesh. And indeed, when we examine the mesh in detail we see the initial distortion on the head is gone (on the left side)

However, the eye bone still has all the vertices associated, but due to the weight value of 0.0 they no longer influence the head.

If you look carefully you see that only the left side of the head has been fixed. Sure that! What we just have done to the Left Eye Bone has to be done again for the Right Eye Bone. So go ahead:

• Unselect all vertices
• Select the mEyeRight bone in the Vertex Groups list
• Select the associated vertices from the “Select” function in the Vertex Groups List
• Assign a value of 0.0 to all vertices in the selected Vertex Group

Now the head is fixed… almost. We still have one more task to do, that is finding not well behaving vertices. Actually we have a few broken vertices in the horse. In the following section i will go into some detail about how Blender can help you to fix vertex groups and single vertex weights.

However this is not a dedicated tutorial about how to skin (weight paint) your model. It just describes the tools which blender has to offer and shows on the horse mesh how the tools play together. I encourage you to do your own experiments here. Knowing the tools is half of the job…

more on finding <em>broken vertices… </em>

Finding broken vertices…

When you skin a mesh, then you sometimes see very bad behaviour in parts of your mesh. There are a couple of reasons why these issues can happen. For example your weighting is not optimal, your model has bad edge flow, etc. However there are a couple of issues which can be spotted easily:

Unweighted verts

Vertices which do not show up in any bone weight group are not affected by any bone movement. This may be even done on purpose, when your mesh contains parts which are meant to be not affected by animation.

Advise: Avoid unweighted verts!

However, for usage in Second Life you have to ensure that each single vertex is weighted to at least one bone. Depending on the viewer version the Mesh importer will either reject the import or the viewer will not display unweighted vertices when the mesh is worn.

Find unweighted
Pure Blender:

• enter Edit Mode
• Select -> Ungrouped verts

With  Avastar

• Open Tool shelf (in any mode)
• Custom Mesh -> Unweighted

Now all unweighted verts are selected.

Fix “unweighted”
Assign selected verts to the most appropriate (often the nearest) bone and give them a weight above 0.0

Unfortunately there is no automatic fix available.
You have to decide on your own to which bone(s) the zero weighted verts shall be assigned and how much weight they shall get.

Zero weighted verts

Vertices can be assigned to one or more bones but all vertex weights sum up to 0.0 Zero weighted verts are somewhat similar to unweighted verts. Blender treats them in the same way, so you would rather keep such verts unweighted instead of assigning zero weight to them.

Advise: avoid  Zero weighted if possible.

However, for usage in Second Life there is a difference. While unweighted verts typically result in errors, zero weighted verts are OK for import to SL. So actually you might get into situations where having zero weighted verts is desired.

Find zero weighted
Pure Blender:

• Not directly supported (see below)

with Avastar:

• Open Tool shelf (in any mode)
• Custom Mesh -> Zero weights

Now all zero weighted verts are selected.

Fix “zero weighted”
Assign a value above 0.0 to at least one of the attached bones. Unfortunately there is no automatic fix available.
You have to decide on your own to which bone(s) the zero weighted verts shall be assigned and how much weight they shall get.

Too many weights on verts

In theory each vertex can be assigned to all skeleton bones. But in practice this is almost never done. Verts are typically assigned to very few bones. having a bone assigned to more than 4 bones is extremely rare. Blender does not impose a limit on the weights per vert.

Advise: Avoid too many weights on bones

However, in Second Life (and with many other game engines) the number of allowed weights per vert is limited typically to 4. So we have to ensure that no vert has got more than 4 weights.

Find too many weighted
Pure Blender:

• Not directly supported (see below)

With Avastar:

• Open Tool shelf (in any mode)
• Custom Mesh -> >4 weights

Now all verts with >4 weights are selected.

Fix “too many weighted”
Remove the weights with the lowest values from the list of assigned vgroups until there are 4 or less vgroups left.

In Weight Paint mode you can use the tool “Limit total” from the tool shelf to automatically reduce the number of weights to a certain limit.

Show unweighted in weight paint mode

When your mesh is in Weight Paint mode you can use a helper tool to show unweighted vertices.

• Open the Tool shelf
• Locate the Options panel
• There enable Show ALL Zero weights

Now all unweighted and all zero weighted vertices will show up in black instead of blue. This is true for Weight Paint mode as well as for Edit Mode, see image.

Well, indeed there is a zero weighted vertex near the eye socket (see image).

However, using a color of black to mark unweighted verts might not be the best choice. Fortunately we can change that…

Change display of Zero weighted

You can change the color used for displaying the zero weighted verts in the Theme editor (in user preferences):

• Open the User Preferences (File -> Userpreferences…)
• Switch to the Themes panel
• Select the 3D View (on the left side)
• Edit the Vertex Group Unreferenced color (see image below)
  

I found magenta is a good alternative setting. But you can experiment and find your own best practice color here.

And this is how the zero weighted verts popup after i changed the color (see image).

Note that you will see a similar spot on the other eye socket as well. Remind this for later fixing.

Editing the Weights of one Vert

When your mesh is in Edit Mode, then Blender displays the list of weights for the active vertex (the last selected vertex) inside the right properties sidebar of the 3D View. Lookup the Vertex Weights Panel (The image displays the weights of an arbitrary selected vertex on the Horse’s head.

This panel is actually a vertex Weight Editor. You can modify each weight of the active vertex, you can propagate the weight of the active vertex to all selected verts, and you even can delete weights from this editor. So lets see what we can do with our broken vertex on the eye socket…

When you select this vertex then you will find exactly one entry in the weight editor showing the eye bone weight is set to 0.0:

So… how can we get another weight into the list ? Well we know this already. We can use the vertex group List as follows:

• Open the Object data Properties to see the Vertex Groups List
• Select the mHead Bone
• In the Weight slider set any value above 0.0
• Hit the Assign button

Now check in the Vertex Weights editor again:

Now we could make this perfect and safely delete the weight from the mEyeRight bone. We can do this because the vertex is also weighted to the mHead bone and all is well.

The previously zero weighted vertex now has one weight that assigns the vertex to the mHead Bone.

So what i have demonstrated on one vertex needs to be done for every other unweighted or zero weighted vertex in your mesh. Actually there is only one more such vertex, on the other side of the head, in mEyeRight. With what you just learned it should be no problem to get this vertex fixed as well.

Find “Zero Weighted” using Poses

There is yet another maybe more intuitive method to find apparently broken weights. The idea is that zero weighted vertices only need to be touched when they appear to move wrong during animation. In practice we will start bending our model in various ways to see if we can find areas where the mesh behaves wrong or weird or both.

Inspect the Head

Lets return back to where the eye bone influences have been reset to zero, but the zero weighted vertices on the eye sockets have not yet been fixed.

Now select the mHead bone (i assume the armature is in pose mode) and bend the head as seen in the image. You already can see the 2 unweighted vertices have not moved along with the head. Now switch to edit mode and select the 2 verts.

From here you have several options to fix the weights. But in any case please remind that currently the mHead Bone is the active bone in the Armature!

Fix from Vertex Groups List

• In the Vertex Groups list set the Weight Slider to a value of about 0.3 the value is not important, it only needs to be above 0.0
• Then Assign this value to the Selected verts.

Immediately the 2 spikes go away. The 2 vertices have snapped into position. That’s all, you are done

Fix with Brushes

Instead of manual setting the weight you also can paint the weight on the mesh.

• Go to Weight Paint mode
• Select a Blur Brush from the Set of available brushes (See top of Tool Shelf)
• now paint on the spikes by wiggeling the brush a bit

Immediately the 2 spikes go away. The 2 vertices have snapped into position. That’s all, you are done

In the image you see the spikes in weight paint mode just before they get painted (and snap into position)

more about Blur

By default, Blender starts the Blur brush stroke intensity (the Strength slider) at 0.2, which is a pretty low value. If needed, don’t be afraid to max it out to 1.0. The image shows the result of such operation. Make sure that there is no dark blue area left in there, a light blue suffices to our needs:

As soon as you start blurring the weights, the 2 spikes go away one by one. The 2 vertices have snapped into position. That’s all, you are done.

 More about “too many weights”

Our Horse indeed has a few vertices with too many weights assigned. Unfortunately Blender has no way to select the offending weights.
However Avastar offers a tool for this as indicated before:

• open the Tool Shelf
• Locate the Avastar Tools section in the Custom mesh panel
• And hit the >4 weights button

Now your mesh will have all verts selected which have more than 4 weights assigned.

Now you can edit each vertex separately and use the Weight Editor to reduce the number of weights until there are 4 weights at maximum. but there is an easier way to go. We have a tool for this. You find the tool in the Tool shelf when you are in Weight Paint mode. It is in the Weight Tools Section and it is named Limit Total.

As soon as you clicked on this tool, 2 events will happen:

1. All vertices with more than 4 weights get some weights removed by starting with the lowest valued weight and continuing until the vertex has 4 weights left over.
2. An Operator panel shows up in the lower left corner of the Tools Shelf. In the operator panel you can change the settings. so you can adjust how many verts shall be capped.

The End

By now we have guided you through a lot of detail information. The course in its current form reflects what we think is important information for your work. You might have become overwhelmed occasionally or bored at other times. However we hope that your overall experience on this entire course was beneficial for your work.

As always we strongly encourage you to give us feedback. We might have missed to include important information. Maybe you found an error or confusing parts. Hence we highly encourage you to give us your Feedback . As this is the very best way to improve the course by any means.

Thanks to everyone who has joined the course and congratulations to all who followed the lessons up to here.

With all the best wishes from

Gaia and Optimo