I've got the book AI Programming Wisdom 3, in the CD-ROM, I've got Bourne and Sattar source code on Autonomous Camera Control, when I see these 2 lines and having not any comments, I am not sure if mvFacing actually means look at vector or look at target, and not sure what mvView and mvCross means? Does anyone here have the same book with me know what these are all about? Thanks Jack

// Autonomous camera class.
class Camera
{
public:
	Vector3		mvPosition, mvView, mvUp;
	Vector3		mvFacing, mvCross;

Update:

I dug a little bit deeper, but found out that mvFacing is actually the lookat vector, but mvCross and mvView has no idea what that is.

Thanks

Jack

Assuming that mvFacing is the look direction, then mvCross is probably the right (or left) vector because it can be calculated by calculating the cross product of mvUp and mvFacing.

I'm not sure about mvView. My guess about mvView is that it is the position the camera is looking at. So mvFacing = mvView - mvPosition.

Can you post the code where those vectors are initialized?

mvCross is most likely the right or left vector of the camera that represents its x-axis. mvCross is obtained by a cross-product between the camera's direction vector and the up vector; that's why it's called mvCross. By moving along this vector you can create the so called strafe effect of a camera.

To create the lookAt matrix (most cameras calculate this matrix) you need a direction vector and a target vector. The direction vector is the vector that's pointing in the direction your camera is facing and this one is usually obtained from subtracting the position vector from the target vector. Based on the way the variables are set up I assume the first 3 vectors are the user-supplied vectors thus mvView is most likely the target vector (e.g. the coordinate a camera is looking at like (0,0,0)) while the mvFacing and mvCross are then later calculated thus mvFacing is then probably the camera's direction vector.

I don't know if the original authors are willing to let me disclose the source code...
But here is the constructor method

//
//    Camera::Camera()
//
//    Default constructor.
//
Camera::Camera()
{
    mnCurrentProfile = 0;
    mnNumOfProfiles = 0;

    mvPosition = Vector3::origin;
    mvView = Vector3::origin;
    mvUp = Vector3::yAxis;
    mvFacing = Vector3::origin;
    mvCross = Vector3::origin;
    
    mfSecondsUntilEnd = 1.0f;

    mnRayCastingMethod = kCameraCurrent;
    mnSafePointMethod = kSafePoint_targetrelative;

    mfFrameTime = 0.0f;

}


//
//    Camera::~Camera()
//
//    Default destructor.
//
Camera::~Camera()
{
}

Hello friends,
I've tried to connect the camera from the book to an Ogre camera, this's what I got so far

Ogre::Vector3 BourneVec3ToOgreVec3(Dolly_Cam::Vector3 vec) {
    Ogre::Vector3 vec3;
    vec3.x = vec.x;
    vec3.y = vec.y;
    vec3.z = vec.z;
    return vec3;
}

Dolly_Cam::Vector3 OgreVec3ToBourneVec3(Ogre::Vector3 vec) {
    Dolly_Cam::Vector3 vec3;
    vec3.x = vec.x;
    vec3.y = vec.y;
    vec3.z = vec.z;
    return vec3;
}

cam.mvPosition = OgreVec3ToBourneVec3(mSceneMgr->getSceneNode("Worker00001Node")->getPosition() + Ogre::Vector3(0, 5, 5));
cam.mvFacing = cam.mvPosition - OgreVec3ToBourneVec3(mSceneMgr->getSceneNode("Worker00001Node")->getPosition());
changeDollyCam(cam);

void OgreRecastApplication::changeDollyCam(const Dolly_Cam::Camera& cam) {  
  
        Ogre::Camera* camera = mSceneMgr->createCamera("Dolly_Cam");
        mWindow->removeViewport(0);
        camera->setPosition(BourneVec3ToOgreVec3(cam.mvPosition));
        camera->lookAt(BourneVec3ToOgreVec3(cam.mvView));
        Ogre::Radian R = Ogre::Math::ATan(Ogre::Math::Tan(Ogre::Degree((float)45/2))/mCamera->getAspectRatio())*2;
        camera->setFOVy(R);
    

        mViewport = mWindow->addViewport( camera );
        mViewport->setCamera(camera);

        delete mCameraMan;
        mCameraMan = new OgreBites::SdkCameraMan(camera);
    

}
 

But it looks perhaps at the opposite direction. But I have tried to reverse the order of subtraction to no avail.
To my understanding of vectors, the look at vector should be camera's position substracting the position of look at target.
Correct me if I am any wrong.

Update:

Notice I've got a typo for mCamera => camera in addViewport line, but the result is same
Thanks
Jack

To my understanding of vectors, the look at vector should be camera's position substracting the position of look at target.

cam.mvFacing = OgreVec3ToBourneVec3(mSceneMgr->getSceneNode("Worker00001Node")->getPosition()) - cam.mvPosition;

But it looks perhaps at the opposite direction. But I have tried to reverse the order of subtraction to no avail.

Wait a second. I just pop some figures out

Character Pos: x=-20.0 y=0.0 z=-50.0

Dolly Cam Pos: x=-20.0 y=5.0 z=-45.0

look at vector: x=0.0 y= -0.707 z= -0.707

Anything wrong with these figures?

It seems the look at vector is mirrored in the y axis, from looking down toward negative z to looking down toward positive z

Thanks

Jack