Week 4

Bones & Skinning

Week 4

This week the process of rigging an object was introduced, this is achieved via the use of bones to realistically control the movement of an object, whilst taking into account parent and child relationships. For example when producing the bones to manipulate a character's arm, the shoulder would be the parent bone whereas the children would be the elbow followed by the wrist and then the hand. Whenever the character's arm moves the children bones move initially which then cause the parent bone to accordingly. This relationship can be setup within 3DS Max via the use of "IK Solvers" which allow the user to specify which bones should affect each other.

Bones can be created by accessing the Systems menu under the create tab of the command panel. Bones are drawn by simply click and dragging, by default the first bone created will be the parent, then the proceeding bones will be children in a descending order. Once a bone or string of bones has be made another small object will appear on the end of the lowest child bone hierarchy , this is known as a "nub". Nubs allow quick selection of the lowest child without having to click on the bone itself, i.e. nubs can be used in the same way as a dummy object without having to attach them separately. However a nub's main use is when assigning an "IK Chain" to specify the bones relationships.

An additional parameter of bones is the ability to add "fins" which basically pad them them out resembling "muscle" on a human body. For example when creating bones for the torso of a character fins could be introduced to widen the bones providing a wider structure which can then be skinned.

Once the desired bones have been created, an object may then be placed over the top of them, acting as skin. In order to tell the bone that a certain object should act as its skin, the object should be placed directly over the top of the bone in all viewports, then a "Skin" modifier can be applied. The associated object will then automatically transform when the corresponding chain of bones is moved. This is an extremely useful technique which is invaluable when creating characters, as their bone system can be setup first then the characters limbs can add introduced as skin.

Although skin modifiers are relatively straightforward to apply they will not always produce the desired affect when the bones are moved. Consequently the "Envelopes" sub-object level of the skin modifier can be adjusted. Envelopes allow the user to determine which vertices are affected by the skin modifier, this is indicated by a visual balloon/selection area which encircle certain vertices changing their colour according to the amount they will be affected. Blue represents vertices that won't be fully considered by the modifier, the ideal colour is either orange or red.

Having learnt how to setup a bone system and rig an object to act as its skin, I experimented by creating a simple leg to test these features. To begin with the bones were produced starting with the hip and ending at the foot. "HI Solvers" were then used to specify the appropriate relationships between the number of bones. HI Solvers can be found under the Animation --> IK Solvers menu along the main toolbar along the top of the user interface. The HI Solvers were inserted by clicking on the "hip" parent bone , then dragging down and clicking on the "heel" bone. These HI Solvers are represented by small blue crosses, that can also be attached to any spline object which in turn will act as a dummy object to move the HI Solver without having to click on it each time. Additional HI Solvers were then placed between the "heel", "foot" and "toe" bones.

I then proceeded by creating the actual leg itself using the box tool to produce a rough leg and foot shape. The vertices were then scaled around certain points and a mesh smooth modifier was applied to add more definition to the leg. Whilst producing the leg I ensured that it was constructed around the bones rather than having to move it over them afterwards which may have proved problematic, resulting in the leg having to be reshaped for example. As a result I gathered that this would serve as good working practice for the future, in that producing the bones first followed by the skin over the top of them is essential.

Producing the bones afterwards would be inefficient and difficult to work with. Consequently I will take these factors on board when producing my idents for this Semester's assignment, as producing a working/realistic character is one of my goals and the techniques I have learnt should prove essential to achieving this.

Although I am relatively pleased with how the leg turned out it is far from perfect. This was due to the fact that I struggled setting up the envelopes on the leg's skin and as a result several of the polygons become inverted during the animation sequence. Consequently if I spent longer tweaking the size and position of the envelopes I believe I could eventually solve this issue, however as it is only a basic demonstration of how bones can be used it is not of great concern.