function [frame_index, gaze_x, gaze_y, marker, eye_found] = load_eye_tracking_data(filename)
% [frame_index, gaze_x, gaze_y, marker, eye_found] = load_eye_tracking_data(filename)
%
% Loads the eyetracking data stored in the specified file. Raises an error,
% if the file was not found.
% 
% Arguments:
%           filename: string, the path to the data file
%
% Returns:
%           frame_index: vector, the recorded frame numbers
%           gaze_x, gaze_y: vector, the recorded x and y eye positions
%           marker: vector, the recorded event marker
%           eye_found: vector, 1, or zero values indicating whether or not
%           the eye was actually detected by the tracker.

if exist(filename, "file") ~= 2 
   error("file %s does not exist or is no mat file", filename);
end

load(filename, "gaze_x", "gaze_y", "frame_index", "marker", "eye_found")