Car Race Game IV

Review — where we got to 5 min

• Off the track is more friction — 0.8 instead of 0.9.
• ask () and wait fills one place called answer.
• A page’s buttons are costumes on one sprite, cloned by a My Block.
• A broadcast moves you from one page to the next.

Quick-fire

You click 2 Players and the game moves to the next page. How does the race find out there are two players?

Today’s Topic 3 min

• Remembering what the player chose
• Sensible defaults
• A race that sets itself up from the choices
• A 3-2-1 countdown
• Two ways to win, judged in one place

Learning outcome

By the end of this lesson you will be able to:

1. Carry a player’s choice across pages with a variable.
2. Show or hide a sprite depending on what was chosen.
3. Write two different win conditions that end the same way.

Learnt — joining it up 28 min

A broadcast carries nothing

This is the idea of the lesson, and it is easy to walk past. When you broadcast [Game Mode v], the message says where to go. It does not say who sent it or why.

So a button that only broadcasts has thrown your choice away. It has to remember first:

if <(costume [name v]) = [2 Players]> then
  set [players v] to (2)
  broadcast [Game Mode v]
end
            

The five things to remember

• players — 1 or 2
• game mode — Time Race or Lap Race
• track — Track 1 or Track 2
• laps to win — how many
• race time — how long

Defaults, before anything else

What if the player never visits a page? Set every one of them to something sensible when the flag is clicked:

when flag clicked
set [players v] to (1)
set [game mode v] to [Lap Race]
set [track v] to [Track 1]
set [laps to win v] to (3)
set [race time v] to (60)
            

The race reads, it does not decide

When Game Play arrives, nothing has to be worked out. Every sprite just looks at the variables.

The Stage picks the backdrop:

when I receive [Game Play v]
if <(track) = [Track 1]> then
  switch backdrop to [Track 1 v]
else
  switch backdrop to [Track 2 v]
end
            

The blue car only turns up if it was asked for:

when I receive [Game Play v]
hide
if <(players) = (2)> then
  go to x: (30) y: (70)
  point in direction (90)
  show
end
            

Three… two… one…

A new sprite with four costumes: 3, 2, 1 and GO!.

Each one does exactly the same thing — appear small, grow, hold. Four times. So make a block:

define Pop
set size to (40) %
show
repeat (12)
  change size by (8)
end
wait (0.4) seconds
            

when I receive [Game Play v]
switch costume to [3 v]
Pop :: custom
switch costume to [2 v]
Pop :: custom
switch costume to [1 v]
Pop :: custom
switch costume to [GO! v]
Pop :: custom
hide
broadcast [Game Start v]
            

Two ways to win

Your player chose a game mode. Now honour it:

• Lap Race — wait until somebody reaches the lap target.
• Time Race — count the clock down, then see who did the most laps.

when I receive [Game Start v]
if <(game mode) = [Lap Race]> then
  wait until <<(P1 lap) = (laps to win)> or <(P2 lap) = (laps to win)>>
else
  repeat until <(race time) = (0)>
    wait (1) seconds
    change [race time v] by (-1)
  end
end
            

Then one comparison decides it, whichever mode was played:

if <(P1 lap) > (P2 lap)> then
  set [winner v] to [Red]
else
  if <(P2 lap) > (P1 lap)> then
    set [winner v] to [Blue]
  else
    set [winner v] to [Nobody]
  end
end
broadcast [Play Again v]
            

Basic — join the menu to the game 24 min

Step 1 — the five variables and their defaults

Make them, and add the defaults stack to any sprite. It runs once, at the flag, before the menu.

Step 2 — every button remembers

Go through each page and add a set above each broadcast.

Step 3 — the Stage picks the track

Both track backdrops in one project, and one if / else on (track).

Step 4 — the cars line up

On when I receive [Game Play v]: hide, then go to the right start position for the chosen track, reset speed, steering and laps, then show. Blue does all of it inside if <(players) = (2)> then.

Step 5 — the countdown

New sprite, four costumes, the Pop block, and broadcast [Game Start v] at the end. Change the cars’ driving loop to start on Game Start.

Step 6 — the judge

The two win conditions, the winner comparison, then Play Again.

Step 7 — play it all the way through

Menu → mode → track → race → winner → menu. Twice, with different choices.

Remember the choices

• Five variables, with sensible defaults set at the flag.
• Every button sets its variable before it broadcasts.
• Show them on the Stage while you click through, so you can see it working.

The race obeys

• The chosen track appears.
• One player means one car — the blue car is not on screen at all.
• The cars start on the line and wait for the countdown.

Somebody wins

• Lap Race ends when a car reaches the lap target.
• Time Race ends when the clock runs out, and the leader wins.
• A draw says so.
• The Play Again page names the winner and offers Play Again or Back to Menu.

Setting, and How to Play

Your menu has two buttons that still do nothing. The deck’s last mission is to finish them.

• Setting — ask for the number of laps, the race time and each player’s name, and use them.
• How to Play — a page that explains the controls, with a way back.

Summary 5 min

• A broadcast says where to go. A variable says what was asked for. You need both.
• Give every setting a default before the player sees anything.
• The race reads the variables. It does not decide anything itself.
• A My Block is worth making even with no inputs — the countdown proves it.
• Two win conditions can end the same way, so the rest of the game stays simple.

Default

What a setting is before anybody changes it.

State

Everything the game currently knows: page, choices, scores.

Game mode

A different way to win the same game.

Draw

Nobody wins. Worth handling — it happens more than you think.

Hand in

Share your finished Car Race and send the link to your teacher. That is the second arc done — next lesson starts the Shooting Game.