Tracks

A track is a collection of frames, along with some information about how to interpolate them. Typically, a track class would contain the following members.

template<typename T, int N>
class Track {
protected:
    std::vector<Frame<N>> mFrames;
    Interpolation mInterpolation;
public:
// Rest of the class
}

typedef Track<float, 1> ScalarTrack;
typedef Track<vec3,  3> VectorTrack;
typedef Track<quat,  4> QuaternionTrack;

Representing a track this way means that each component is tied to the same time on the timeline. You can’t make a keyframe in the X component of the track without also adding a keyframe to the Y and Z components as well. The vec3 track below shows how the X, Y and Z components of the vector have keyframes at the same time values, even if those frames are not needed.

The most important function of the track is Sample. The signature of this function takes a floating point number and a boolean, the function returns a floating point number.

template<typename T, int N>
T Track<T, N>::Sample(float time, bool looping);

The Sample function starts byadjusting the time argument to be valid. For the time to be valid, it must fit within the start and end times of the track. Next, the function finds the frame index at the atjusted time. This way, you can increment a timer, pass it in to the Sample function, and assign the result of the Sample function to that timer variable. The Sample function will kep the timer in a proper range.