   Tile-based scrolling and Bitmap-based scrolling
  In a book I'm reading, it says: with "Bitmap-based scrolling" you can scroll in any direction even diagonally which you cannot do with tile-based scrolling.I'm not sure why I cannot scroll diagonally with tile-based scrolling?! I mean in both cases, tile-based and bitmap-based, I get input from the user, read a window size and pass it to the back buffer. If the user tried to move diagonally, vertically or horizontally, it is just an X,Y coordinate at the end, correct?   
  I'm not sure exactly why you couldn't move diagonally in tile-based scrolling, unless the book meant something like the original pokemon games, where literally everything in the game was, practically speaking, a big array of tiles.   