About the grassy field tutorial

i’ve examined the tutorial from the beginning to the end.
i presume that the width of the area where all the movies dulpicate is the same as the width of the canvas?

how does this happen? i don’t see a code that says how far the duplicated movies can go.

when i make the same thing but in a more wide canvas it still is just that little area…

how can you make a very wide field of grass? lets say 600pixels

thanks in advance for helping me out,