User Interfaces - Game Programming Algorithms and Techniques - page 259

// Grab player position
...
// The new facing of the arrow is the normal-
ized vector
// from the player's position to the waypo-

int.

facing = waypoint - playerPosition
facing .Normalize()

// Use the dot product to get the angle
between the original
// facing (0, 0, 1) and the new one
float angle = acos(DotProduct( Vector3 (0, 0,
1), facing ))
// Use the cross product to get the axis of
rotation
Vector3 axis = CrossProduct( Vector3 (0, 0, 1),
facing )
Quaternion quat
// If the magnitude is 0, it means they are
parallel,
// which means no rotation should occur.
if axis .Length() < 0.01f
quat = Quaternion .Identity
else
// Compute the quaternion representing
this rotation
axis .Normalize()
quat = CreateFromAxisAngle( axis , angle )

end

// Now set the final world transform of the

arrow

ComputeMatrix( worldPos , quat )

end

end