One of my all-time favourite books is Masters of Doom. I've been reading it since Doom3 was released, but upon reading it again I'm confused on something in the chapter "Dangerous Dave...".
The team was busy working away on the vertical shoot-em-up Slordax, and it clearly shows smooth vertical scrolling for the background. However, when John Romero discovers the "Super Mario Bros 3" Demo one morning, hes blown away by smooth horizontal scrolling. What puzzles me is why would he be so shocked when John Carmack had already achieved scrolling in Slordax?
Is there a difference in difficulty in programming a vertical-scrolling background and that of a game such as Super Mario Bros? Surely scrolling is scrolling whether vertical or horizontal?