Graphics Programming in 3D - Essentials of Interactive Computer Graphics - page 449

vec3 CModel::ComputePlanePosition() {
// initial plane position P oc

p

A:

vec3 planePos(0,0,0);
.
// plane node transform M p Source file.

Model _ AimPlane.cpp

file

UWB _ XformInfo planeXf=m _ PlaneNode->GetXformInfo();
.
planeXf.SetUpModelStack(dh); // load M p to top of matrix stack
dh.TransformPoint(planePos); // compute P wc

B:

in the Model folder of the

D3D _ Orientation project.

= P o p M p

p

.
return planePos; // return plane position in WC: P wc

p

Listing 16.14. Computing the plane position in WC.

The negation reflects the fact that the initial front direction of the plane points
toward the negative z -axis. Notice that the upward direction of the plane is in the
y -axis direction of the WC, or

V u = 001 .

Now we can compute V s according to Equation (16.6),

V u ×

V s = V f .

In order to ensure V u is perpendicular to the other two axes, we must compute

V u = V f × V s .

Lastly, we must normalize all three vectors to compute V u , V f ,and V s for com-
ponents of the rotation matrix in Equation (16.5). Listing 16.14 shows that we
can compute the plane WC position ( P w p ) by observing that in OC space, P oc

p is
simply the origin. At label A, we initialize the plane OC position P o o to be the
origin. At label B, we use the plane's scene node transform ( M p ) to compute the
plane's position in WC space P w p .
In the following discussion, we separate the discussion of the ComputePlane
Rotation() function into three separate listings: Listing 16.15 presents how we
compute the plane-to-tiger direction V f . Listing 16.16 describes using a rotation
matrix to aim the plane toward the tiger. Finally, Listing 16.17 describes us-
ing quaternion rotation to aim the plane toward the tiger. Listing 16.15 shows the