Graphics Programming in 3D - Essentials of Interactive Computer Graphics - page 459

void CModel::ComputeArrowTransform( float sec) {
A:

vec3 arrowFront(0,0,-1); // V o m initially is -z axis
mat3 Ra=m _ ArrowNode...GetRotation(); // R a arrow node rotation
arrowFront = arrowFront * Ra; // V w m = V o m R a

.

B: // Similar to Listing 16.13 : Computing forward direction and moving forward

// arrow velocity is defined by the current V w m
vec3 arrowV = arrowSpeed * arrowFront;
// arrow node gets the new velocity
m _ ArrowNode.SetVelocity(arrowV);
// move the arrow node
m _ ArrowNode.MoveNodeByVelocity( sec );
.
// compute V f

C:

vec3 dirToTiger = ...
// length of V f . if this is short, then it means
float dist = length(dirToTiger);
// the arrow is close to the tiger. Hit! We are done.
if (dist < 1.0f) return ;
.

D:

// Similar to Listing 16.18 : Gradual alignment with V f using slerp
// to compute

V w m · V f )

float cosTheta=dot(arrowFront,dirToTiger);
.
vec3 rotAxis=cross(arrowFront,dirToTiger); // V b =

θ b = acos (

V w m ×

V f )

V b , θ b )

// q b =( quat qb = quatFromAA(rotAxis, theta);

// compute and set q a and q c
.
// q new is linear combination of q a and q c
quat newQ = slerp(qa, qc, homeInRate);
. // sets the new rotation to the arrow scene node XformInfo

}

Listing 16.20. Computing homing-in functionality.

Source file.
Model _ FireArrow.cpp

file

re-compute the velocity according to the up-to-date forward direction. At label
C, V f , the vector between the arrow and the tiger is computed and tested. If this
vector is short, it means that the tiger and the arrow are close by. We will register

in the Model folder of the

D3D _ Orientation project.