Hi Martin,
what the manual fails to mention is that each data point also carries an event type. Fixations are detected in semi-real time and the data is reported like this:
1. The user’s eyes fixate on something.
2. The EyeX Engine detects that a fixation has started and sends the data packet (Begin, X, Y, Timestamp) to the client
3. The fixation goes on for a while. The EyeX Engine sends data packets: (Data, X, Y, Timestamp). The gaze point will only move slightly since we’re in a fixation.
4. The fixation ends. When the EyeX Engine detects the end of the fixation, it sends a data packet (End, 0, 0, Timestamp).
So if all you want is the fixation duration: store the timestamp from the Begin packet and compute the duration when you get the next End packet.