Hi @eyerpheus, yes indeed there will be always a minimum size limit for the user defined gazeable area.
Consider that eye tracking accuracy will always be limited by biological considerations such an inherent jittery movements of the eye and that the eye ball itself will not move if focus is shifted only by a few millimetres, meaning that accuracy is not a technological limitation of the eye tracker itself.
Accordinly, you will need to ensure that the distance between stimuli is sufficient to account for this within the design of your program. I don’t have the exact figure for minimum size of gazeable area, but I will try to get you those numbers.
Certainly, you are on the right track using the Rectangle class, so no need to go with polygonal class as it seems the shapes you are trying to cover are roughly square rotated 45 degrees.
Will the greater distribution between successive radio buttons be particularly problematic for the project?