I played around with it for a while, and it seems that the displayed lines are limited to the window size instead of the actual buffer.
With this I mean, that for example I have a 500 lines buffer and a window size that only allows to show 25 lines, right? Those 25 lines show the last 25 lines of the program and the other 475 buffer spaces are black lines.
I'll attach some pictues with the maximum window size that my screen allows, and I changed the letters to numbers so it's more visible.
I'm sorry if there's something I'm not getting. Other IDEs I used just printed everything and then you could scroll up and down normally.