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Part II: Home Entertainment

For example, say you’re watching cable TV and you decide to watch a

movie. The component video input on the TV is already active. If enabling

DVD mode indiscriminately tells your TV to switch to component video

inputs, your TV will assume that since it’s already using component video

inputs it should cycle to the next component input. By “managing state,”

you can switch the TV input only when necessary.

Think of your TV as being in one of two states with respect to the inputs

you’re using: component video or S-Video. Similarly, the receiver can be in

one of three states for modes that require the TV: DVD, VCR, and TV. In

LUA, all variables are

global: the state of a variable defined in one script

is available to all scripts unless declared using the

local keyword. So, you

can create two state variables to indicate what the current state is. To keep

track of which input on the TV is currently active, create a variable called

tv_mode; create another variable, receiver_mode, to watch over the state of

the receiver’s modes. We’ll use strings as the values of the variables in this

project, but integers or even bitfields would work fine, too. The following

table shows the two state variables and their possible values.

Variable Possible values

tv_mode component

s-video

receiver_mode dvd

vcr

tv

Now, instead of blindly trying to switch my ...