These are the three main ingredients for any menu. We'll talk about some special features of video and subpictures that
make menus possible, and then describe the buttons themselves.
All of the information specific to menus is contained in the PCI packet, part of the NAV Pack.
As you can see from the Button Information Table there's a lot more to a button
than just some color changes. The first thing we need to know is where these color changes are to take place. This
is a rectangle described by Starting X, Ending X, Starting Y, and Ending Y. These areas can overlap, and combined with
different color schemes for the overlapped areas, can be used very creatively.
The next thing that the table contains is used for navigation by the cursor keys (or joystick on some players), it gives
the next button above, below, to the left, and to the right of the button being described. As you can see, the player knows
nothing of the geometry, and some bizarre navigation can be defined here.
The last thing in the table is one, yes only one, command to execute if the button is actioned. Does this sound
restrictive? Well, it's really not. Most commands can do more than one thing, such as go to another menu and define the
button to be selected (also called highlighted) on entry.