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Hi @rasa, what I would recommend is that at each 0.5 second interval you calculate the distance (call it stimulus point distance) between the start location and end location using Pythagoras theorem and with this “stimulus point distance” you can determine the approximate angle travelled relative to the user.
For example: let’s say at time=0 : stimulus location = (100,100) pixels
at time=0.5 : stimulus location = (200,250) pixels
=> distance travelled = sqrt ((200-100)^2 + (250-100)^2) = 180.27 Pixels = 4.86 cm (refer to previous post link to calculate)
=> angle travelled between stimulus points = tan-1 (4.86 cm / 30 cm (user distance) ) = 9.2 Degrees
This simplified way of doing things does make some rather large assumptions such that you are using the average distance between the stimulus screen plane and users eye and not the actual distance between the stimulus point and the user eyes and indeed that the user distance is unchanged between stimulus points.
That being said, if you follow this simplified workflow you should be able to get the numbers you need. Let me know how you get on.