hip bone is the root of the raptor's body bone hierarchy to which the legs, tail, and torso are attached. The
hip bone serves as a control bone with which we can adjust the entire raptor body.
The vertices of the thigh mesh attachments are weighted to the the
hip bone, in addition to the bones making up the raptor's legs. This helps to keep the vertices at the edge of the meshes in the correct place when the
hip bone is rotated.
The raptor's front and back legs are setup in the same way. For brevity, we will only discuss the front leg in detail. The leg is driven by two IK constraints:
The two-bone IK constraint
front-leg-ik controls the
front-leg2 bones, while the two-bone IK constraint
front-foot-ik drives the
front-foot1 bones. Note that the order in which those two IK constraints are applied to the bones is important. We first apply the
front-leg-ik constraint and then the
front-foot-ik constraint. The order in which constraints are applied is defined by their order in the
Constraint node of the tree view.
These two IK constraints target bones outside the raptor body bone hierarchy:
front-leg-goal. Moving the target bones will cause the IK constrained bones to follow. This allows us to easily bend the leg or bend the heel.
At the tip of the leg, we have the
front-foot1 bone and its child bone
front-foot2. We disabled
Inherit Rotation for
front-foot2 to ensure the foot doesn’t go through the ground when rotating its parent bone.
front-leg1 bone is the only bone in this leg bone hierarchy that has a slot containing an attachment. The vertices of the
raptor-front-leg mesh attachment are weighted to the the leg bones, deforming smoothly when the bones are transformed.
The upper body of the raptor is composed of a single mesh attachment
raptor-body. Its vertices are weighted to the bones making up parts of the upper body, like the torso and the tail.
raptor-body image has the tail in a straight line to improve its deformation when bending it in either direction. As a general rule, if a mesh needs to be bent in either direction then the mesh image should be straight when the bones are bound.
The jaw is represented by the
raptor-jaw mesh attachment. Like the thighs of the raptor, the vertices around the pivot of the jaw have been weighted to the
head bone. This ensures that the jaw does not look disconnected from the rest of the head when it is rotated.
To give the jaw a 3D look, the
jaw bone contains another bone called
jaw-inside which contains a copy of the
raptor-jaw mesh. The mesh is scaled down and tinted to be slightly darker than the front of the jaw. Note that the tongue of the raptor is drawn between the two jaw attachments.
Moving the horn bones
horn-back independently from each other adds a slight 3D effect to the head, making it appear as if the head is rotating side to side.
The horn bone hierarchy also contains the
spineboy-front-arm-goal bones to help ensure Spineboy always has a good grip on the horns.
Spineboy's hip bone
spineboy-hip is attached to the
saddle bone on top of the raptor. Transforming the hip bone will move Spineboy's body, while four IK constraints, one for each leg and hand, are used to keep Spineboy's feet in the stirrups and his hands on the raptor's horns.
The two IK constraints
spineboy-back-arm-ik place Spineboy's hands on the IK targets
front-arm-target, which are attached to the raptor horns. The
spineboy-front-arm-ik constraint drives the
front-bracer bones, while the
spineboy-back-arm-ik constraint drives the
back-bracer bones. Since Spineboy is holding the raptor's horns in most animations, the IK constraint
Mix values are set to
100% in setup mode.
Mix values of the arm IK constraints are set to
100%, the arm and bracer bones are driven entirely by inverse kinematics. For the
gun-grab animation, Spineboy needs to let go of the horns to grab his gun, so the arm and bracer bones need to be driven by bone transformation keys instead of the IK constraints.
To disable the influence of the IK constraints, their
Mix values are set to
0% on frame
0 of the
The gun in the holster is an attachment in the
gun slot. When Spineboy grabs the gun, that attachment is hidden while the
front-hand slot is switched to an image of the hand holding a gun. This happens in frame
7 in the
Attach: gun and
Attach: front-hand timelines.