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Quaternion camera movement

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I'm implementing a quaternion camera, but I've got an anoying problem I can't figure out. I can rotate my camera around with the mouse and it works fine, but when I try to move along the direction of the camera, the Y and X components aren't correct unless I'm looking down the +ve Z-axis. As I turn, the Y component of the direction goes from being correct when looking down +ve Z, to 0 when looking either +ve or -ve X, then to -ve of what it should be when looking down -ve Z. The net result is that if you look forwards and up, you actually move forwards and down. Also, if you look to the side, you move in the -ve sideways direction of what you should. Here's some of the code I'm using:
//------------------------

// Function : Sets the quaternion's values

//

// Parameters : Angle, axis

//

// Returns : -

//------------------------

void CQuaternion::Set(float angle, float x, float y, float z)
{
	// Convert angle into radians.

	angle *= (3.141592654f / 180.0f);

	// Normalize the axis.

	float mag = sqrtf((x * x) + (y * y) + (z * z));
	x /= mag;
	y /= mag;
	z /= mag;

	// Calculate the first value

	m_fQuat[0] = cosf(angle / 2.0f);

	float sinHA = sinf(angle / 2.0f);
	m_fQuat[1] = x * sinHA;
	m_fQuat[2] = y * sinHA;
	m_fQuat[3] = z * sinHA;
}
//------------------------

// Function : Generates a 4x4 matrix from the quaternion

//

// Parameters : Pointer to a 4x4 matrix

//

// Returns : -

//------------------------

void CQuaternion::GetMatrix(float * mat)
{
	// Normalise the quaternion

	Normalise();

	// Get local, easier to read copies of the values

	float x = m_fQuat[1];
	float y = m_fQuat[2];
	float z = m_fQuat[3];
	float w = m_fQuat[0];

	float xx = x * x;
	float yy = y * y;
	float zz = z * z;

	// Set the matrix

	mat[0] = 1.0f - 2.0f * (yy + zz);
	mat[4] = 2.0f * ((x * y) + (w * z));
	mat[8] = 2.0f * ((x * z) - (w * y));
	mat[12] = 0.0f;

	mat[1] = 2.0f * ((x * y) - (w * z));
	mat[5] = 1.0f - 2.0f * (xx + zz);
	mat[9] = 2.0f * ((y * z) + (w * x));
	mat[13] = 0.0f;

	mat[2] = 2.0f * ((x * z) + (w * y));
	mat[6] = 2.0f * ((y * z) - (w * x));
	mat[10] = 1.0f - 2.0f * (xx + yy);
	mat[14] = 0.0f;

	mat[3] = 0.0f;
	mat[7] = 0.0f;
	mat[11] = 0.0f;
	mat[15] = 1.0f;
}
This is how I'm getting my direction for the camera. What I'm doing is multiplying M * V where M is the matrix from the quaternion and V is a vector looking down -ve Z (0, 0, -1). Hence, it simplifies down to -1 * the third column of the matrix.
//------------------------

// Function : Converts a rotation to a direction

//

// Parameters : Rotation quaternion

//

// Returns : Direction vector

//------------------------

SVector DirectionFromRotation(CQuaternion &q)
{
	SVector out;
	float mat[16];
	
	q.GetMatrix(mat);
	out.x = -mat[8];
	out.y = -mat[9];
	out.z = -mat[10];

	return out;
}
EDIT: Source tags --------------------------------------- Let's struggle for our dream of Game! http://andrewporritt.4t.com [edited by - f8k8 on April 10, 2004 9:48:53 AM]

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I got it. It was the DirectionFromRotation function if anyone''s interrested.

I''ve only just learned Quaternions, this is how it should be:


CQuaternion vecq;
vecq.SetVals(0, 0, 0, -1);
CQuaternion conjq = q;
conjq.Inverse();

vecq.PostMultiply(q);
vecq.PreMultiply(conjq);

return vecq.GetAxis();



---------------------------------------

Let''s struggle for our dream of Game!

http://andrewporritt.4t.com

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