Rotating one object to face another C++ - c++

Question

I am trying to rotate a an object (a car) to face an object however I am having quite a bit of difficulty with it.
I've had varying success with this code, it knows when the angle is correct and will stop rotating when if it manages to face the right way but most of the time it gets stuck rapidly twitching due to the sign value flicking from 1 > -1 or from -1 > 1 every single frame, thus causing all rotation to stop and for the car to just twitch uncontrollably and never really correct itself.
Honestly, I'm not sure if my Sign calculation is using the correct values as the car moves on the X/Z axis but rotate on the Y-axis to turn left/right
I'm using C++ and DirectX11 by the way
Any advice/help would be appreciated, thanks in advance!
bool ParticleModel::FaceTarget(XMFLOAT3 target)
{
XMFLOAT3 toNormalize;
toNormalize.x = transform->GetPosition().x - target.x;
toNormalize.y = transform->GetPosition().y - target.y;
toNormalize.z = transform->GetPosition().z - target.z;
XMFLOAT3 toTarget = NormalizeVector(toNormalize);
//Determine the angle between the heading vector and the target.
XMFLOAT3 carHeading;
carHeading.x = sin(transform->GetRotation().y);
carHeading.y = sin(transform->GetRotation().x);
carHeading.z = cos(transform->GetRotation().y);
carHeading = NormalizeVector(carHeading);
double angle = acos(DotProduct(carHeading, toTarget));
//Return true if the player is facing the target.
if (angle < 0.01000)
{
return true;
}
/*if (signTimer < signCooldown)
{
signTimer++;
}
else if (signTimer >= signCooldown)
{
signTimer = 0;
sign = GetSign(carHeading, toTarget);
}*/
sign = GetSign(carHeading, toTarget);
transform->SetYRot(transform->GetRotation().y + (0.030f*sign));
//bool thing = false;
//RotateHeadingByRadian(angle, mHeading.Sign(toTarget));
return true;
}
float ParticleModel::DotProduct(XMFLOAT3 a, XMFLOAT3 b)
{
float dot;
dot = (a.x * b.x) + (a.y * b.y) + (a.z * b.z);
return dot;
}
int ParticleModel::GetSign(XMFLOAT3 v1, XMFLOAT3 v2)
{
if (v1.y*v2.z > v1.z*v2.y)
{
return -1;
}
else
{
return 1;
}
}

Answer 1

It's ok I found out how to do it, essentially this is now the code
XMFLOAT3 distance;
distance.x = transform->GetPosition().x - target.x;
distance.y = transform->GetPosition().y - target.y;
distance.z = transform->GetPosition().z - target.z;
XMFLOAT3 carHeading;
carHeading.x = sin(transform->GetRotation().y);
carHeading.y = sin(transform->GetRotation().x);
carHeading.z = cos(transform->GetRotation().y);
if (VectorLength(distance) < 0.5)
{
return true;
}
//Don't actually need to call normalize for directionA - just doing it to indicate
//that this vector must be normalized.
XMFLOAT3 directionA = carHeading;
XMFLOAT3 directionB = NormalizeVector(distance);
float rotationAngle = (float)acos(DotProduct(directionA, directionB));
if (abs(rotationAngle) < 0.5)
{
return true;
}
XMFLOAT3 rotationAxis = CrossProduct(directionA, directionB);
rotationAxis = NormalizeVector(rotationAxis);
transform->SetYRot(transform->GetRotation().y + (rotationAngle*rotationAxis.y));