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A First Person Camera Class in OpenGL C++

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#1Obi-Dan  Members   -  Reputation: 109

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Posted 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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#2Vincent_M  Members   -  Reputation: 809

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Posted 05 March 2013 - 01:14 PM

So, you'd like the literally have the camera move in the direction the camera is facing, even along the Y-axis? For example, if you're looking 45 degrees up, you'd like the camera to move up the Y-axis?

If this is the case, then you would want to add this line to your MovableObject::moveForward() method:

m_position.y += sin(m_rotation.x) * distance;


Keep in mind, that sin() and cos() give you the normalized components of a vector along the unit circle. Using sin() and cos() with x and z will give you a direction vector with the length of 1 because it's normalized. When you add m_position.y into the mix, you're actually making the direction vector longer than 1 unit (before you scale it by distance).

The best thing to do is find your direction vector, normalize, then multiply by distance like so:

void MovableObject::moveForward(float distance)
{
Vector3 direction;
direction.x = -sin(m_rotation.y);
direction.y =  sin(m_rotation.x);
direction.z =  cos(m_rotation.y);
direction.Normalize();

// add the direction, scaled by distance, to the current position
m_position += direction * distance;
}


Depending on your coordinate system, you may want to change direction.x to +cosf() and direction.z to -sinf(). You'd also want to scale your "distance" float by the elapsed time between frames in your update loop if it's not already so it moves smoothly regardless of framerate.

#3Obi-Dan  Members   -  Reputation: 109

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Posted 06 March 2013 - 04:51 PM

Brilliant! Thanks, that works perfectly for moving forward. What about the change pitch method?

All I need now is to be able to rotate, currently the camera rotates on the Y axis only which lets me move around but not up or down.

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