Skinning

Skinning is the process of attaching vertices to bones. The vertices can be viewed as the "skin". Once the vertices are attached to the bones skeletal animation can occur.

There are two ways to do skinning: manually and automatically. Both are specific to the bone selection mode.

Manual

Using the Manual Skinning tool it is possible to adjust how each bone influences each vertex. Open the Ninja example scene. Activate the Manual skinning tool.

A white square with a green border is now shown over each vertex. The white square indicates the influence of the selected bone. At this point no bone is selected. Select a foot bone.

Notice with the foot bone selected the vertices that are influenced by this bone are black. Black indicates that a vertex is influenced by the selected bone. White indicates a vertex is not influenced by the selected bone.

Click a white vertex. Note that it changes to black indicating it is now influenced by the selected bone.

Shaper allows for vertices to be influenced by more than one bone. This is an advanced form of skeletal animation. Setting a vertex to be influenced by more than one bone requires the weight value to be set. The sum of the weights for a particular vertex must equal 1. For example, for a particular vertex one bone could weigh 0.25, another could weigh 0.5 and another 0.25.

Change the weight value to 0.25 and click on a vertex. Notice that the vertex is not black, instead it is grey. The closer to black the vertex is the higher the weight.

Automatic

Manual skinning can be a tedious process. Shaper provides the Automatic Skinning tool which will use some basic rules to attach the vertices to the bones. Activate the Automatic Skinning tool.

The Automatic Skinning tool works by assigning bone influence based on distance. The closer a vertex is to a bone the higher the bone's influence on the vertex will be.

The first field on the dialog controls the maximum distance between a vertex and a bone for the bone to influence the vertex. Shaper chooses a value based on the model. In general it should not be necessary to change this value.

Some times it is not appropriate for the bone closest to a particular vertex to influence that particular vertex. For example, the ninja has been modelled with the hands down. Some of the waist vertices are actually closer to the hand bone than the hip bone. Situations like this are handled by doing a ray check as part of the automatic skinning. The ray effectively prevents bone influence from going through the "skin". Bones can only influence vertices that a straight line can be drawn between without going through a face.