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Obi-Dan

Member Since 04 Mar 2013
Offline Last Active Mar 11 2014 06:51 PM

Topics I've Started

Matrix Yaw and Pitch

07 March 2013 - 07:15 AM

I'm trying to create a first person style camera in OpenGL as part of my coursework. 

This question is more about matricies and vectors so I thought the Math section would be best.

The camera has a 4x4 matrix containing position, rotation etc. also it has a look-at and right vector. (I think I need an up vector too)

 

Currently the camera is able to move forwards in the direction it is facing or strafe from side to side:

 

void moveForward(float distance)
{
	m_lookatVec.x = -sin(m_rotation.y);
	m_lookatVec.y = sin(m_rotation.x);
	m_lookatVec.z = cos(m_rotation.y);
	m_lookatVec.normalise();

	m_position += m_lookatVec * distance;
}

 

This works well when moving down the z axis but the up/down direction seems to flip when travelling up the z axis i.e. when facing upwards the camera moves down on the y axis or up on the y axis when facing downwards.

 

void moveRight(float distance)
{
	m_rightVec.x = cos(m_rotation.y);
	m_rightVec.y = sin(m_rotation.x);
	m_rightVec.z = sin(m_rotation.y);
	m_rightVec.normalise();

	m_position += m_rightVec * distance;
}

 

Not sure if this method is correct, I sort of guessed it but it seems to work!

 

The other issue is with changing the direction of the camera. Rotating around the y axis is easy enough but I would like to be able to change the pitch too. At the moment the Y axis or Yaw is changed like so:

void changeYaw (float degrees)
{
	float rads = MathHelp::degreesToRadians(degrees);
	m_rotation.y += rads;
}

 

 

The rotation vector is later added to a transform matrix with the translation and scale vectors and applied to the camera before rendering.

void Camera::Update()
{
	GUMatrix4 transform, translation, rotation, scale;
	
	GUVector3 rot = getRotation();

	// Create matricies
	translation = GUMatrix4::translationMatrix(getX(), getY(), getZ());
	rotation = GUMatrix4::rotationMatrix(rot.x, rot.y, rot.z);
	scale = GUMatrix4::scaleMatrix(1.0f, 1.0f, 1.0f);

	glMatrixMode(GL_PROJECTION);

	transform  = getProjMat() * scale * rotation * translation;

	glLoadMatrixf((GLfloat*) &transform);

}

 

 

I now need a changePitch method, changeRoll isn't really necessary right now. I'm also guessing the changeYaw method should change to use the up, look and right vectors but I'm not entirely sure how to use them.

 

Any help would be awesome!

Thanks, Dan.

 

 


A First Person Camera Class in OpenGL C++

05 March 2013 - 07:09 AM

I'm trying to create a first person style camera.
So far I have moving along the x and y axes sorted and now need to work on changing the pitch of the camera.

E.g. To move forward 2.5f units:

 

mainCamera->moveForward(2.5f);

Camera is derived from MovableObject:

void MovableObject::moveForward(float distance)
{

	m_position.z += cos(m_rotation.y) * distance;
	m_position.x -= sin(m_rotation.y) * distance;
}

 

 

m_position - position vector

m_rotation - rotation vector (in radians)

 

The camera update method sorts out the matrix stuff...

 

void Camera::Update()
{
	GUMatrix4 finalMat, translation, rotation, scale;
	
	GUVector3 rot = getRotation();

	// Create matricies
	translation = GUMatrix4::translationMatrix(getX(), getY(), getZ());
	rotation = GUMatrix4::rotationMatrix(rot.x, rot.y, rot.z);

	glMatrixMode(GL_PROJECTION);

	finalMat = getProjMat() * rotation * translation;

	glLoadMatrixf((GLfloat*) &finalMat);	

}

 

translation - the 4x4 translation matrix.

rotation- the 4x4 rotation matrix.

 

The code above works beautifully for moving forwards on the x and z axes. At the moment the camera is rotated about the Y axis using the mouses horizontal movement. 

 

void mouseMove(int x, int y) {

	if (mDown) {

		int dx = x - mouse_x;
		int dy = y - mouse_y;

		// rotate camera 
		if (mainCamera)
		{
			
			mainCamera->setYaw(mainCamera->getYaw() + (float)-dx);
				
		}
		
		mouse_x = x;
		mouse_y = y;
	}
}

 

I now want the camera to rotate about the x and z axes using the mouses vertical position. The camera then needs to move forwards with the Y axis included.

 

So far for changing the cameras pitch I have:


void MovableObject::changePitch(float degrees)
{
        // Convert change to radians
	float rads = MathHelp::degreesToRadians(degrees);
	
        // X rotate more when looking down Z axis
	m_rotation.x += cos(m_rotation.y) * rads;
}

 

 

 

Hopefully this is making sense to somebody. 

 

Thanks in advance!

Dan.

 

 


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