Camera and User Interaction - WebGL Game Development - page 190

vec3.cross(this.up, this.dir, this.left);
vec3.normalize(this.up, this.up);
vec3.cross( this.left , this.up, this.dir);
vec3.normalize(this.left , this.left);
}
}

Understanding the yaw function for the orbit camera
The orbit camera's yaw function algorithm is as follows:

If the orbit point and position are the same, perform the following steps:

1. We calculate the rotation quaternion from the global up vector [0,1,0] and not

from the camera up vector as follows:
quat.setAxisAngle(quate,[0, 1, 0], angle);

2. The camera position does not change. We transform each vector with the

quaternion like we do in the free camera as follows:
vec3.transformQuat(this.dir, this.dir, quate);
vec3.transformQuat(this.left, this.left, quate);
vec3.transformQuat(this.up, this.up, quate);

3. Compute unit vectors for all three vectors.

If the orbit point and camera position are different, perform the following steps:

1. Create a rotation quaternion around the global up vector as follows:

quat.setAxisAngle(quate, [0,1,0], angle);

2. Calculate the new position after transforming the old position with a

quaternion. This calculates a new position relative to the origin.
vec3.transformQuat(newpos,this.pos,quate);

3. Transform the position from relative to origin to relative to orbit point

as follows:
vec3.add(this.pos,newpos, this.orbitPoint);

4. Calculate the direction vector from the orbit point and new position, and

calculate the unit direction vector as follows:
vec3.subtract(this.dir,this.orbitPoint, this.pos);
vec3.normalize(this.dir,this.dir);

5. Calculate the up vector after transforming it with the quaternion as follows:

vec3.transformQuat(this.up, this.up, quate);