# first-person camera

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Hey, My doubt concerns this article: A Simple Quaternion-based camera. Specifically, this method:
void Camera::SetViewByMouse(void)
{
// the coordinates of our mouse coordinates
int MouseX, MouseY;

// the middle of the screen in the x direction
int MiddleX = SCREENWIDTH/2;

// the middle of the screen in the y direction
int MiddleY = SCREENHEIGHT/2;

// vector that describes mouseposition - center
Vector MouseDirection(0, 0, 0);

// static variable to store the rotation about the x-axis, since
// we want to limit how far up or down we can look.
// We don't need to cap the rotation about the y-axis as we
// want to be able to turn around 360 degrees
static double CurrentRotationX = 0.0;

// The maximum angle we can look up or down, in radians
double maxAngle = 1;

// This function gets the position of the mouse
SDL_GetMouseState(&MouseX, &MouseY);

// if the mouse hasn't moved, return without doing
// anything to our view
if((MouseX == MiddleX) && (MouseY == MiddleY))
return;

// otherwise move the mouse back to the middle of the screen
SDL_WarpMouse(MiddleX, MiddleY);

// get the distance and direction the mouse moved in x (in
// pixels). We can't use the actual number of pixels in radians,
// as only six pixels  would cause a full 360 degree rotation.
// So we use a mousesensitivity variable that can be changed to
// vary how many radians we want to turn in the x-direction for
// a given mouse movement distance

// We have to remember that positive rotation is counter-clockwise.
// Moving the mouse down is a negative rotation about the x axis
// Moving the mouse right is a negative rotation about the y axis
MouseDirection.x = (MiddleX - MouseX)/MouseSensitivity;
MouseDirection.y = (MiddleY - MouseY)/MouseSensitivity;

CurrentRotationX += MouseDirection.y;

// We don't want to rotate up more than one radian, so we cap it.
if(CurrentRotationX > 1)
{
CurrentRotationX = 1;
return;
}
// We don't want to rotate down more than one radian, so we cap it.
if(CurrentRotationX < -1)
{
CurrentRotationX = -1;
return;
}
else
{
// get the axis to rotate around the x-axis.
Vector Axis = CrossProduct(View - Position, Up);
// To be able to use the quaternion conjugate, the axis to
// rotate around must be normalized.
Axis = Normalize(Axis);

// Rotate around the y axis
RotateCamera(MouseDirection.y, Axis.x, Axis.y, Axis.z);
// Rotate around the x axis
RotateCamera(MouseDirection.x, 0, 1, 0);
}
}


My problem is that my CurrentRotationX is only < 1 or > -1 for the first mouse movements, and then it goes >1 and the camera never moves again... Does anyone have any idea of what the problem might be ? Thanks

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Got it to "work" with gametutorial.com's code:

void Camera::onMousePassiveMotion(int x, int y)	{		int middleX = (int)_winWidth  >> 1;				// This is a binary shift to get half the width		int middleY = (int)_winHeight >> 1;				// This is a binary shift to get half the height		float angleY = 0.0f;							// This is the direction for looking up or down		float angleZ = 0.0f;							// This will be the value we need to rotate around the Y axis (Left and Right)		static float currentRotX = 0.0f;				// If our cursor is still in the middle, we never moved... so don't update the screen		if( (x == middleX) && (y == middleY) ) return;				// Set the mouse position to the middle of our window		glutWarpPointer(middleX, middleY);										// Get the direction the mouse moved in, but bring the number down to a reasonable amount		angleY = (float)( (middleX - x) ) / 500.0f;				angleZ = (float)( (middleY - y) ) / 500.0f;						// Here we keep track of the current rotation (for up and down) so that		// we can restrict the camera from doing a full 360 loop.		currentRotX -= angleZ;  				// If the current rotation (in radians) is greater than 1.0, we want to cap it.		if(currentRotX > 1.0f)			currentRotX = 1.0f;		// Check if the rotation is below -1.0, if so we want to make sure it doesn't continue		else if(currentRotX < -1.0f)			currentRotX = -1.0f;		// Otherwise, we can rotate the view around our position		else		{			// To find the axis we need to rotate around for up and down			// movements, we need to get a perpendicular vector from the			// camera's view vector and up vector.  This will be the axis.			btVector3 tmp = _lookAt - _position;			btVector3 vAxis = tmp.cross(_up);			vAxis = vAxis.normalize();						// Rotate around our perpendicular axis and along the y-axis			RotateView(angleZ, vAxis[0], vAxis[1], vAxis[2]);		}				// Rotate around the y axis no matter what the currentRotX is		RotateView(angleY, 0, 1, 0);	}

However... the movement is VERY jerky... and not smooth at all...
Any ideas?

Thanks again!

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Nevermind, everything's good now!

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