I think I may have done in my poor little immune system with my ill-considered Saturday marathon of coding and candy. But nothing takes the mind off a gestating stomach bug like climbing the old ivory tower!
So here's a short little blurb on relative vision (player vision) in shmups - such as Gradius.
There are two kinds of shmups. Those that are top-down and racing towards the top of the screen, and those that are side-view and racing towards the right. One wonders why some people prefer the one and some people prefer the other. I am here to tell you one of the primary differences. Maybe two, if attention span permits.
The difference is in relative vision. NOT player vision, as you might expect. The difference is that player vision is, quite simply, what the player sees. Relative vision takes into account how fast and wide the player's response options are.
In a side-scrolling shmup, the ratio of responses to vision is pretty low. You see things pretty far in advance, but you are in a cramped 'tunnel'. This dramatically limits your maneuverability. Dodging along the wide axis is not very useful, as that is the axis which the bullets are travelling along. When you're running from a train, you don't run along the tracks, you run OFF the tracks. Same theory here: you dodge on the vertical axis, because the horizontal axis is usually the 'track'. This is reflected in the fact that your side-view ship is almost always needle-shaped, increasing the 'grain' of the vertical axis in comparison to the horizontal one. Effectively giving you 'more space to dodge'.
Making this whole dodging thing worse is the fact that such games have BOTH axes 'weighted' - things tend to travel towards the 'back', as mentioned, but most games also have weapons which use pseudo-gravity and 'fall' along the vertical axis. This makes your dodging even tighter, especially since your ship is not shaped politely to be able to dodge vertical shots.
Now, let's compare to games where you proceed along the Y axis instead. You have a lot more places you can move, but you can't see as far in comparison. You'll notice that most horizontal games have shots which are almost all either vertical, horizontal, or gravity-arcing... and usually come in single shots or short bursts due to the difficulty of dodging. Vertical games, on the other hand, tend to have long, spiraling sprays of bullets. Why? Because you have a lot more freedom of movement. You can DODGE easier.
You'll notice most vertical games take a peculiar tactic: ships come on screen... but remain 'dormant' for a second before firing. Some ships fire after having cruised along most of the screen. Some ships actually STOP and STAND STILL for a precious half-second before firing. This makes up for the bad player vision, similarly to the needle-shaped ship in a horizontal shooter making up for the bad maneuverability.
Lastly, vertical shmups don't have the 'gravity' problem. Gravity in a vertical shmup, if it exists at all, is along the vertical axis. This still leaves the horizontal axis uncompromized for dodging purposes. This also allows for Symmetry, which I'll talk about later.
Interesting how it all pans out, isn't it? Hindsight is 20/20, but it's pretty clear that the difference in relative vision is the biggest difference between the two subgenres of shmup. Knowing how to take advantage of the differences is the key.
I prefer vertical shmups. Some people think that the extra room is 'wasted' - too much empty space off to each side that the player won't "use". I don't think that's true. That empty space can be used to stage ships that haven't fired yet, as listed above. You can't get that kind of population with a horizontal shooter, because the space is just too cramped.
And now you know. I'd love to hear your opinions, but if you have any, you're probably WAYYYY to into shmups. :)