6. Modular Panel and Events

Right now we have to open the computer, press the start button and then get the output in the console.

This it not really user-friendly, instead it would be nice, if we could press a button in the game, and the computer updates a screen or sign or something.

For this we first want to get the "button press" working. Here we gonna rely on the Modular Control Panel to create a hardware control panel.

To figure out how it works, we will ignore our current code and just focus on the panel stuff, later we will combine them.

Modular Control Panel

After you have unlocked the "Modular I/O" schematic in the HUB you can build a modular control panel.

You can build a Large Vertical Control panel, and you will see it consists of three actual panels where you can place things on.
These panels have panel-index that start at 0 from the bottom.
Bottom Panel 0, Center Panel 1 and Top Panel 2.

The Large Control panel is similar just with one panel of index 0.

Each panel is like a x-y-graph and coordinate system.
The origin (0, 0) is in the bottom left corner, The X-Axis goes to the right and the Y-Axis goes up.

You can now place different module onto the panels.

You can then use in Lua the modular control panels getModule(x,y,p) function to get a module at a given position on the given panel.
The first parameter is the X-Position, the second parameter is the Y-Position and the third parameter is the panel-index. The function returns a reference to the given module.

Many modules are larger than just one module slot (f.e. a switch is 1x2 module-slots). The same module can be referenced over all the occupied module-slots.

On the control panel we will place a normal button module and connect the panel to our computer.

First we need to get a reference to our panel.

local panel = component.proxy("...")

After that we want to get the reference to the module using the getModule funciton.

local btn = panel:getModule(0,0,0)

Change the coordinates according to your button placement and remove the third parameter if you have used the Large Control Panel.

The normal button module has a setColor(…​) function that allows you to change the color and light emission of the button head.


The above code should make the button light up bright red.

The whole code:

local panel = component.proxy("...")
local btn = panel:getModule(0,0,0)

Component Signals / Events

Now we want to print some text to the console, when the button gets pressed.
For this we have to have a look at component signals.

Component Signals are a way for components to notify computers about different things. The way they do it is different from events.
Events (aka. interrupts) would pause your normal code execution and execute an interrupt routine instead.
FicsIt-Networks doesn’t do that, instead you have more control over, when you actually want to handle such a signal.

Ironically the API we need is called event.

With the signal system the computer has to first tell the different components, that it wants to receive their signals. This is especially useful because in large systems you would be constantly be spammed with signals you probably don’t even care about.

You can use the event.listen(…​) function to listen to components.
It is a variadic function that takes component references as parameters and tells those components that this computer wants to listen to signals.

The counterpart is event.ignore(…​) that works the same as event.listen(…​).
The difference is, it tells the component to stop sending signals to this computer.

You can also use the event.ignoreAll() function, to essentially call the ignore function on all components the computer is currently listening to.

Each computer has its own signal queue.
This signal queue holds all unprocessed signals a computer has received.
When the computer receives a new signal from a component, the signal will be added to the top of the queue. If the queue is full, then the new signal will simply get discarded.
To empty the queue, you can either clear all signals at once, unprocessed, or you simply process all signals.

To clear the signal-queue at once you can use the event.clearAll() function.
Often you want to call this right after your computer started, because the queue may still contain old signals.

To finally actually process signals you have to pull() them from the stack.
One pull returns the "oldest" signal.
If the queue is empty, the pull function "blocks". That means your code will wait, till there is a signal available and returns that.
Everytime you get the "oldest" signal, it will be removed from the queue.

The problem now is, your code can not do anything as long as there is no signal. So you can not f.e. update a clock, or a blinking light.
As solution, the pull function takes a "timeout" parameter.
This parameter allows you to define after how many seconds the pull should return anyway, if it does, the pull function will return nil.

If no parameter is given, the pull function will wait indefinitely for the next signal.
If 0 is given, the pull function will return immediately in the same Lua tick if there is no signal available.
If 0.0 is given, the pull function will yield the current Lua tick and return immediately in the next Lua tick. If a number greater than 0.0 is given, the pull function will wait that amount of seconds till it returns nil.

When a signal is received and your code is already waiting for the timeout, the function will return immediately with that new signal.

When you wait for a signal but also do some other stuff in the meantime (using timeout), so you call the pull function over and over again. This is called polling.

A signal can have a variable amount of parameters that are emitted with it. That is why the pull function returns either nil for no signal or some return values that are always present and the variable parameters of the signal.

The return values of valid signal are:

  1. The signal internal name.
    The signal internal name is specified by the type of the signal and allows you to identify the different types of signals because it is a unique name.

  2. The signal sender reference.
    The second return value is a reference to the signal sender which you can use to identify the exact source of the signal. We can f.e. check if it is the same as a reference we already have or use the hash of it as table key.

  3. The third and all following return values are the parameters that got emitted together with the signal.

local eventName, signalSender, val1, val2, ... = event.pull(...)

Finishing our event sample code

As mentioned, we want to print some text when the button gets pressed.
The button emits a signal when it gets pressed, that means we first want clear the queue and then listen to the button.



Next thing we need is to create an infinite loop in which we can poll the signals.

while true do

Inside this loop we will wait indefinitely for a signal and get that signal.

local e, s = event.pull()

Followed that we will check if the signal sender is our button and if the event is the Button Press "Trigger" event.

if s == btn and e == "Trigger" then

Inside this if we can then do the things we want to do, when the button gets pressed. In out case, print some stuff to the console.


Out complete code should be something like:

local panel = component.proxy("...")
local btn = panel:getModule(0,0,0)



while true do
    local e, s = event.pull()
    if s == btn and e == "Trigger" then