Maze Escape II

Review — where we got to 5 min

Last lesson the walls became solid.

• The maze is one sprite, at (0, 0), the size of the Stage.
• Move, ask touching [Maze v]?, step back by the same amount.
• The exit is a sprite, and touching it ends the game.

Quick-fire

Your maze has one route from start to exit. Why does nobody play it twice?

Today’s Topic 3 min

• Collectibles: a sprite that hides when you touch it
• change [gems v] by (1) — counting what you picked up
• A hidden sprite touches nothing, which is how a door opens
• broadcast [got key v] — the key tells the door

Learning outcome

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

1. Put collectibles in a maze and count them.
2. Make a door that is solid until something opens it.
3. Reset everything so the second game is the same as the first.

Learnt — collecting, hiding, opening 27 min

1 · A collectible hides

A crystal you pick up is a sprite that hides itself and adds one to a number. It is not deleted — you need it back next game.

when flag clicked
go to x: (60) y: (-120)
show
wait until <touching [Beetle v]?>
change [gems v] by (1)
hide
            

1. Make a variable called gems and tick it so it shows.
2. On the player, add set [gems v] to (0) under its flag hat.
3. Add a Crystal sprite and give it the stack above.
4. Play. Drive into the crystal: it goes, and the number goes up.
5. Press the flag again. The crystal is back and the number is 0.

2 · A hidden sprite touches nothing

This is the fact the whole lesson turns on, and it is worth saying out loud: a hidden sprite is not touching anything. Not the player, not a wall, nothing.

So a door that is solid can become a door you can walk through, by hiding.

if <key [left arrow v] pressed?> then
  change x by (-4)
  if <touching [Maze v]?> then
    change x by (4)
  end
  if <touching [Door v]?> then
    change x by (4)
  end
end
            

3 · The key sends a message

The key does not open anything. It hides itself and shouts, and the door opens itself. You have seen this shape before — it is the music video’s cues.

when flag clicked
show
wait until <touching [Beetle v]?>
broadcast [got key v]
hide
              

when flag clicked
show

when I receive [got key v]
hide
              

Two sprites that know nothing about each other, joined by a message. That is why you can add a second door later and it needs no new code — it just listens too.

Basic — fill the maze 25 min

Open your maze from last lesson. Add one thing at a time and play after each.

Step 1 — one crystal

1. Make the variable gems and show it.
2. Add set [gems v] to (0) to the player’s flag stack.
3. Add a Crystal, put it in a corridor, and give it the five-block stack.
4. Play, collect it, and press the flag to check it comes back.

Step 2 — three crystals

1. Right-click the crystal and duplicate it twice.
2. Change each copy’s go to x: () y: () to a different corridor.
3. Play. All three should count into the same number.

Step 3 — the door

1. Add a sprite for the door and put it across a corridor near the exit.
2. Give it a flag stack with show.
3. On the player, add a touching [Door v]? step back inside each of the four directions.
4. Play. You should not be able to get past it at all.

Step 4 — the key

1. Add the Key sprite, far away from the door.
2. Give it the wait-and-broadcast stack. Make the message got key.
3. On the door, add when I receive [got key v] and hide.
4. Play the whole maze: key first, then door, then star.

Step 5 — play it twice

1. Finish it, then press the flag.
2. Crystals back, key back, door shut, gems at 0.
3. Anything still missing needs a show.

Three things worth having

Put three collectibles in your maze, in places that are out of the way.

• Each one hides when collected and adds to the same number.
• None of them is on the direct route to the exit.
• All three come back when the flag is pressed.

A locked way out

Put a door between the player and the exit, and hide the key somewhere they have to go and find.

• The door is as solid as a wall until the key is taken.
• The key is a long way from the door.
• After the key, the door is gone and the way out is clear.

All of them, or nothing

Take the key away. Now the door opens only when every crystal in the maze has been collected.

• Two crystals is not enough. Three is.
• The player can see how many they have.
• The door opens the moment the last one is taken, not a second later.

when flag clicked
show
wait until <(gems) = (3)>
hide
            

The one that is not a crystal

Somewhere in your maze is something that looks exactly like the others and is not. Touch it and you are back at the start with nothing.

• The decoy looks like a real collectible.
• Touching it sends the player back to the start.
• It does not disappear, so it is still there next time round.
• Somebody who has played once can learn where it is.

when flag clicked
show
forever
  wait until <touching [Beetle v]?>
  broadcast [caught v]
  wait (1) seconds
end
            

Summary 4 min

The maze now has decisions in it, and they all come from three small facts.

1. A collectible hides and counts. show at the start brings it back.
2. A hidden sprite touches nothing, so hiding is how a door opens.
3. A key does not open a door. It broadcasts, and the door opens itself.
4. Watching a number is the other way to open a door, and it is just as correct.

Collectible

A sprite that hides when touched and adds to a count.

Locked door

A sprite that is solid like a wall until something tells it to hide.

wait until

Holds a script until a question is true. Neater than a forever with an if in it.

Reset

The show and the set-to-0 that make the second game the same as the first.

Next lesson: something in the maze starts moving, and it is not on your side.