pxt-calliope/docs/projects/rps-teams.md

Rock Paper Scissors Teams

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Massively multi-player rock paper scissors!

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Playing rock paper scissors is usually a two player game... but it works with much more players too! When playing with more than two players, it becomes a team game: all players shake at the same time, then the number of rock, paper, scissors is tallied between all the players. The team with the most players wins the game.

Starting from the basic version of the RPS game, we are going to change the code so that the @boardname@ counts and displays the number of players in the same team. Using the radio communication, the @boardname@ will send its status and receive the status of other boards.

Let's get started!

Starting blocks

Let's start form a . The basic version picks the weapon in a |on shake| event and display an icon accordingly. Take a peek at the code below to refresh your memory on that game.

let weapon = 0
input.onGesture(Gesture.Shake, () => {
    weapon = Math.random(3)
    if (weapon == 0) {
        basic.showIcon(IconNames.SmallSquare)
    } else if (weapon == 1) {
        basic.showIcon(IconNames.Square)
    } else {
        basic.showIcon(IconNames.Scissors)
    }
});

Step 1: Refactoring the rendering

Refactoring is a funny word used in coding which pretty much means reorganizing. In this case, we are going to move the code that displays the rock/paper/scissor icon into its own |forever| loop.

let weapon = 0
input.onGesture(Gesture.Shake, () => {
    weapon = Math.random(3)
})

basic.forever(() => {
    if (weapon == 0) {
        basic.showIcon(IconNames.SmallSquare)
    } else if (weapon == 1) {
        basic.showIcon(IconNames.Square)
    } else {
        basic.showIcon(IconNames.Scissors)
    }
});

Step 2: send status via radio

We send the value of weapon via radio to other @boardname@ in the |forever|. Since radio packet may or may not arrive, it's a good idea to keep sending them.

We also set the radio group and send the device serial number (a number that uniquely identifies a @boardname@) as we will need that later.

let weapon = 0
input.onGesture(Gesture.Shake, () => {
    weapon = Math.random(3)
})

basic.forever(() => {
    radio.sendNumber(weapon)
    if (weapon == 0) {
        basic.showIcon(IconNames.SmallSquare)
    } else if (weapon == 1) {
        basic.showIcon(IconNames.Square)
    } else {
        basic.showIcon(IconNames.Scissors)
    }
});
radio.setGroup(10)
radio.setTransmitSerialNumber(true)

Step 3: the team roster

So all players are constantly broadcasting which face they picked to other players. Let's add the code that receives those status and counts them.

We are going to add an Array variable that contains all the players in the same team as the current player. That array, named players, is like your team roster: it contains the list of @boardname@ serial numbers that have the same weapon as you.

let players: number[] = [0]

Step 4: Receiving a message (part 1)

In an the |on radio received| event, we receive the status from another @boardname@. Click on the *gearwheel to add the serial parameter as we will need it to identify who sent that packet.

We compute three values from the data received:

• match, a boolean value indicating whether the weapon of the other @boardname@ matches our current weapon
• player_index, the position in the array of the other board's serial number. It will be -1 if it is not in the array
• found, a boolean value indicating whether the @boardname@ serial number is part of the players array

let match = false
let player_index = 0
let players: number[] = [0]
let weapon = 0
let found = false
radio.onDataPacketReceived(({ receivedNumber, serial }) => {
    match = weapon == receivedNumber
    player_index = players.indexOf(serial)
    found = player_index >= 0
})

Step 5: Receiving a message (part 2)

There are two cases that we need to handle when looking at match and found:

• if we have a match and the player is not found in the list, then we add it to players
• if we don't have a match and the player is found in the list, then we remove it from players

We turn the two rules above into two if statement where the serial number is added or removed.

let match = false
let player_index = 0
let players: number[] = [0]
let weapon = 0
let found = false
let temp = 0
radio.onDataPacketReceived(({ receivedNumber, serial }) => {
    match = weapon == receivedNumber
    player_index = players.indexOf(serial)
    found = player_index >= 0
    if (match && !(found)) {
        players.push(serial)
    } 
    if (!(match) && found) {
        temp = players.removeAt(player_index)
    }
})

Step 6: reseting the team

What if another player would leave the game? He would stop broadcasting its status and it would stay in our list of players. To avoid this problem, we reset the players array each time we shake:

input.onGesture(Gesture.Shake, () => {
    let players: number[] = [0]
    let weapon = Math.random(3)
})

Step 7: showing team score

The team score is the number of players in that team... which boils down to the length of the players array. We add a |show number| block in the |forever| loop to display it.

let players: number[] = [0]
let weapon = 0
basic.forever(() => {
    basic.showNumber(players.length)
})

The final code

Now it's time to glue all together the pieces of our program. Go carefully through all the steps and assemble the various features. Eventually, it should look like the following program. Download it and plays with your friendssss!

let temp = 0
let found = false
let player_index = 0
let weapon = 0
let match = false
let players: number[] = []
input.onGesture(Gesture.Shake, () => {
    players = [0]
    weapon = Math.random(3)
})
radio.onDataPacketReceived( ({ receivedNumber, serial }) =>  {
    match = weapon == receivedNumber
    player_index = players.indexOf(serial)
    found = player_index >= 0
    if (match && !(found)) {
        players.push(serial)
    } 
    if (!(match) && found) {
        temp = players.removeAt(player_index)
    }
})
basic.forever(() => {
    radio.sendNumber(weapon)
    if (weapon == 0) {
        basic.showIcon(IconNames.SmallSquare)
    } else if (weapon == 1) {
        basic.showIcon(IconNames.Square)
    } else {
        basic.showIcon(IconNames.Scissors)
    }
    basic.showNumber(players.length)
})
players = [0]
radio.setGroup(10)
radio.setTransmitSerialNumber(true)