Making the Applications Interesting - Essentials of Interactive Computer Graphics - page 325

bool CModel::ComputeFrontVelocity( float sec) {

Source file.
Model _ MoveToTarget.cpp
file in the Model folder of
the D3D _ OrientationIn2D
project.

. // code from Listing 12.2 : that computed frontDir= V wc
f

in WC

// Target gray circle's transform
A: txf=m _ pMoveToTarget->GetXformInfo();
// movePt= p wc t (target position)
vec3 movePt = txf.GetTranslation();
// dir= V wc

= p wc
t

− p wc
o

(direction towards target)

t

B:

vec3 dir = movePt - initPos;
// p o is very close to p t => done.
if (length(dir) < 0.1f) return false ;
// vector normalization: compute

V wc
f

V wc
t

and

C:

normalize(frontDir); normalize(dir);
// cos θ =

V w t )
theta = fabs(acosf(dot(frontDir, dir)));
//

V wc
f

V w t ,or θ = acos ( V wc

f

· ·

θ is not very small (zero)

D: if (theta > 0.001f) {

// zDir

V w f × V wc

t

=

E:

vec3 zDir = cross(frontDir, dir);
// aTheta is the current Arm rotation
float aTheta = axf.GetRotationInRadians();
// check sign of z-component from cross product
// to turn clockwise or counterclockwise

if (zDir.z > 0) aTheta += theta * TURN _ RATE;
else aTheta -= theta * TURN _ RATE;
axf.SetRotationRadians(aTheta);
// sets new rotation to M a of Figure 12.3
m _ pArmDrive->SetXformInfo(axf);

F:

}
. // contiune with code from Listing 12.4 : to update new velocity for Arm

Listing 12.3. Step 2: Compute and decrease θ .

computed. Listing 12.3 shows the details of the second step of ComputeFrontVel
ocity() (from Listing 12.1). At label A, the target position p w t in WC is re-
trieved from the appropriate transform. At label B, V w t is computed. The length
of this vector is the distance between the arm origin ( p w o ) and the target. When
this distance is small, the arm has arrived at the target position and we are done.
At label C, the V wc
f

and V wc
t

vectors are normalized, and the angle θ between these

two vectors is computed. A small value represents that the arm is pointing ap-

proximately toward the target. The checking at label D ensures that we do not

θ