Hierarchical Modeling - Essentials of Interactive Computer Graphics - page 297

- SceneNode

M b

C b0 R b1

Body

Right

Left

M la M ra

R a0 R a1 R a2 R a0 R a1 R a2

Arm Arm

M lp M rp

C p0 R p1 C p0 R p1

Palm Palm

Figure 11.14. SceneNode structure for Tutorial 11.6.

components. The scene graph is a more general hierarchy where either scene
nodes or groups of primitives are shared. The sharing of scene nodes or primi-
tives is referred to as instancing. As we will see, instancing allows more efficient
resource utilization; however, the resulting scene graph becomes tricky to control
and maintain. Our source code library does not support instancing.

Tutorial 11.6. Working with a General Scene Tree

Tutorial 11.6.
Project Name:
D3D _ SceneNodeSiblings
Library Support:
UWB_MFC_Lib1
UWB_D3D_Lib11

• Goal. Demonstrate that we can build an arbitrarily complex scene tree
based on the SceneNode class.

• Approach. Design and work with a scene tree hierarchy with multiple child
branches involving more than one generation of descendants.

Figure 11.12 is a screenshot of running Tutorial 11.6. In this tutorial, the simple
arm scene hierarchy is replaced with a more complex two-arm human model.
Figure 11.13 shows the details of the model. The base of the model is defined
by the torso (rectangle R b 1 ) and the head (circle C b 0 ) with pivot position located
at P b (the origin). We see that the CArm hierarchy defines the left and right arms
of the model. In this case, we would like to have control over the entire human
model (e.g., rotating the entire model) while retaining the independent arm and
palm control over the left and right arms.
Figure 11.14 shows an implementation of the human model of Figure 11.13
with five SceneNode objects. In this implementation, the two children of the
Base scene node are both instances of the CArm object from Tutorial 11.5. Notice
that each of the scene nodes has its own transformation operator. In this case,
M b is the transformation operator of the Body node, and M la and M lp are the
operators for the left Arm and Palm nodes, whereas M ra and M rp are the opera-
tors for the right Arm and Palm nodes. Listing 11.11 shows the implementation
of Figure 11.14 in the CModel class.

Figure 11.12. Tutorial

11.6.

R b1

C b0
P b

Left

Right

Figure 11.13. Model for

Tutorial 11.6.

At label A, we see the m _ Body defining