because that is what they are x0, y0, x1, y1, in relation to the screen and the linked tutorial.
its very confusing to talk about things outside of the raw code with personal names.
it may be good practise in your own code but i am talking mostly when giving examples.
I don't want scroll though code to know the line i am reading it regarding pin 0, because this will then be subjective to the comment quality of the person coding and it being clear and well laid out
sensor = map(analogRead(0), 0, 1024, 0, 180);
sensor = map(potread1), 0, 1024, x, y);
from a beginners perspective its very hard to process all the functions and then decipher the values of made up names, again from a example code.
anyway thank again for your help
Why call them confusing x0 and x1 again And the constness of length...
But note, sin and cos are terrible slow. Fine if it's quick enough but don't look weird if your loop() turns out to be slow.