Storm Flight III — Scratch L3 Lesson 23

Learnt28 min · freezing one script, then all of them
Basic24 min · press P, with a sign that says so
Challenge 1–327 min · the runaway, the timer, and a pause that looks paused
Extrabonus · slow motion

WHAT IT SHOULD LOOK LIKE

Press P and the whole sky stops where it is. Press it again and everything carries on from exactly there — which is the hard part.

playing

paused — nothing has moved

panels run left to right

Review — last lesson 5 min

Touching a bolt costs a life; the last one sets the state to over.
A collision is tested every frame, so a hurt flag is what stops one touch being sixty.
The cool-down lives in its own script, because a wait in the main loop would freeze the game.

Quick-fire

Last lesson a wait in the wrong place froze the game by accident. Today you want to freeze it on purpose. Is the answer a wait?

Reveal the answer

Almost — it is wait until, which is different. A plain wait stops for a length of time you choose. wait until stops for as long as a condition says so, which is exactly what a pause is.

Today’s Topic 3 min

wait until <(state) = [play]> at the top of every loop
A key that toggles between two states
Pausing clones, and pausing a clock
Making a pause look paused

Learning outcome

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

Stop and restart a whole game with one key.
Find the one script that ignored the pause, by measuring it.
Say why Scratch’s timer is no use to a game that can be paused.

Learnt — stopping, and starting again 28 min

1 · A fourth state, and a key that toggles

Add paused to your states. The key that switches between it and play is a toggle — it asks where it is and goes the other way:


when [p v] key pressed
if <(state) = [play]> then
  set [state v] to [paused]
else
  set [state v] to [play]
end

The same “ask before you act” shape as the space bar in Lesson 3-21. One key, two meanings, no confusion.

2 · One block freezes a script

Put wait until <(state) = [play]> at the top of the loop body. While the game is paused the script sits there doing nothing at all; the moment the state goes back it carries on from exactly where it was.


repeat (40)
  wait until <(state) = [play]>
  next costume
  change x by (8)
  change [ticks v] by (1)
end
say [Forty ticks - however long you held P.] for (2.5) seconds

The loop still runs exactly forty times. Pausing changes how long that takes, not what happens.

WHAT IT SHOULD LOOK LIKE

One block does it. `wait until <state = play>` at the top of the loop parks the script and costs nothing while it waits.

forty ticks, however long you paused

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then press P a few times as the parrot crosses the Stage.

Forty ticks, every run, however long you paused for. That is what resume means.

Why not stop this script? Because a stopped script cannot start itself again, and it would forget where it was. Pausing is waiting, not stopping. Keep stop for things that are genuinely finished.

3 · Every loop, in every sprite

One sprite pausing is not a pause. Every loop that moves anything needs the same block — and that includes the loop inside a clone, because each clone is running its own copy:


when I start as a clone
show
repeat until <(x position) < (-230)>
  wait until <(state) = [play]>
  change x by (-6)
end
delete this clone

A star drifting across the sky. Thirty clones, thirty copies of this loop, thirty waits — and they all stop on the same frame.

WHAT IT SHOULD LOOK LIKE

Three sprites, the same one block each, and the Stage stops together. A clone waits too — the wait goes inside the clone's own loop.

all three asking

Runs here in the page. Nothing to install.

How to use this: Click the green flag, fly with the arrows, then press P. Look at the stars and the bolt, not the parrot.

Three sprites and a crowd of clones, all stopping together.

Basic — press P 24 min

Open last lesson’s Storm Flight. Stars to collect, and a pause that works.

Step 1 — stars to fly through

Add the Star sprite. Under the flag it hides and becomes a spawner.
Its loop: wait until playing, go to the right-hand edge at a random height, clone itself, wait about half a second.
The clone script: show, then drift left until off the edge, then delete.
Inside the drift loop, test touching (Parrot v)? — add a point and delete the clone.

Step 2 — the pause key

Add the toggle script from above to the Parrot.
Count pauses while you are there, so you can prove it fired.

Step 3 — the wait, everywhere

Put wait until <(state) = [play]> at the top of the parrot’s flying loop.
The same at the top of the star spawner’s loop.
The same inside the clone’s drift loop. This one gets forgotten.

Step 4 — the sign

Add a sprite to be your sign — a plain button costume is fine — and put it near the top of the Stage.
Its whole script is a forever loop: if the state is paused, show and say PAUSED - press P; otherwise hide.


when flag clicked
hide
go to x: (0) y: (120)
forever
  if <(state) = [paused]> then
    show
    say [PAUSED - press P]
  else
    hide
    say []
  end
end

The sign never needs telling. It watches the state, like everything else.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, collect a few stars with the arrow keys, then press P. Press P again to carry on.

What you are aiming at. Thirteen stars collected, one pause, and nothing lost across it.

The parrot stops but the stars keep coming.

The star spawner’s loop has no wait, or it has one but the clone’s drift loop does not. Check both.

Pressing P does nothing.

The toggle is checking = against a word that does not match — Paused is not paused here because you typed it twice differently. Copy the word rather than retyping it.

P pauses but will not resume.

You used two if blocks rather than if / else. The first sets the state to paused, and the second immediately sees “paused” and sets it back — so it flickers, or never changes.

The sign appears but nothing else freezes.

The sign is the only script asking. That is Challenge 1 — every other loop needs the wait.

The parrot jumps forward when I resume.

The wait is below the movement rather than at the top of the loop body, so one more step was taken before the pause took hold.

CHALLENGE 1 · L3-23-M1🪙 30 Adcoins8 min

The runaway

Find the script that ignored the pause by measuring it rather than squinting at the Stage.

Give the parrot a tick counter and the bolt a tick counter.
The parrot’s loop waits; the bolt’s does not.
Pause for a few seconds and compare the two numbers.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — one script with a plain forever loop and no wait. The parrot froze at 173 ticks; the bolt sailed on to 241.

paused, and one sprite did not notice

Runs here in the page. Nothing to install.

How to use this: Click the green flag, let it run, press P, and wait. Watch the two counters separate.

Parrot 173, bolt 241. The gap is exactly how long the game was paused for.

Done when: your two counters are equal before the pause and different after it, and you can say which script is the liar.

Teacher note

Counting is the technique, not the answer. On a real project with twelve scripts, a temporary counter in each one finds the runaway in a minute, where watching the Stage can take twenty. Worth naming as a debugging habit — it is the same idea as Lesson 3-46’s say-tracing.

CHALLENGE 2 · L3-23-M2🪙 50 Adcoins9 min

The clock that will not pause

Put Scratch’s own timer on the Stage next to a clock you keep yourself, and pause the game.

Show the built-in timer readout.
Keep your own my time, changed only while playing.
Pause for several seconds and compare.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — Scratch's own timer runs on real time and pauses for nobody. A clock the game controls has to be a variable you keep yourself.

paused for three seconds

Runs here in the page. Nothing to install.

How to use this: Click the green flag, watch both clocks, then hold the pause for a few seconds.

My time stops dead. The built-in timer does not — it measures real time, not game time.

Done when: the two clocks agree before the pause and disagree afterwards by roughly the length of the pause.

Teacher reveal — and a trap worth showing


forever
  wait until <(state) = [play]>
  wait (0.5) seconds
  change [my time v] by (0.5)
end

Why halves and not tenths. Add 0.1 to a variable sixty times and Scratch shows 7.699999999999989. Computers store 0.1 as an almost-but-not-quite value and the error piles up. Halves and quarters are stored exactly, so they add up cleanly. Show them the broken version first — it is a thirty-second demonstration of something most adults never find out.

CHALLENGE 3 · L3-23-M3🪙 70 Adcoins10 min

A pause that looks paused

Freezing is not enough — a player needs to see that it was deliberate.

Every sprite dims while the game is paused.
The sign appears over the top.
Resuming undoes all of it, with nothing left dim.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a pause that looks paused. Everything dims by the same amount, and resuming undoes all of it.

dimmed

Runs here in the page. Nothing to install.

How to use this: Click the green flag and press P. Everything on the Stage dims together, and brightens on resume.

Brightness −35 on every sprite, cleared on resume. A frozen game without this just looks broken.

Done when: pausing and resuming five times leaves the Stage looking exactly as it started.

Teacher note

The failure to watch for is a sprite that dims but never brightens, because its “clear” only runs in a branch that the resume does not reach. Ask them to pause and resume repeatedly — the dimming stacks up and the Stage goes black, which makes the bug obvious and memorable.

EXTRA MISSION · L3-23-MX🪙 100 Adcoinsbonus

Slow motion

Prove your state machine is not just an on/off switch. Add a slow state: the same game, running at a quarter speed.

The S key toggles between play and slow.
The pause still works from either of them.
The flying loop runs in both, with a wait added only in slow.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, press S for slow motion, P to pause, S again to speed up.

A fourth state, and the same loop serving all of them.

Teacher note

The “going further” answer: once states differ only by a number, they should be a number. play/slow/fast is three states doing one job; a speed variable does it better. States are for situations that behave differently, not for settings — and that distinction is what Lesson 3-24’s difficulty menu is built on.

Summary 5 min

wait until <(state) = [play]> at the top of a loop body is the whole of pause.
Every loop needs it — including the one inside a clone.
A toggle key uses if / else, not two ifs.
Scratch’s timer measures real time and cannot be paused. Keep your own.
Add 0.1 repeatedly and the number goes wrong. Halves and quarters are exact.
A pause must look paused, and resuming must undo all of it.

Pause: A state in which everything waits, keeping its place.
Toggle: A control that switches between two things each time you use it.
Game time: Time that only passes while the game is being played.
Runaway script: A loop that never asks the state, and so never stops.

Hand in

Save your game. Next lesson finishes the arc: a score, a best that outlives the round, and a menu that adds one more state.

Learnt28 min · freezing one script, then all of them
Basic24 min · press P, with a sign that says so
Challenge 1–327 min · the runaway, the timer, and a pause that looks paused
Extrabonus · slow motion

WHAT IT SHOULD LOOK LIKE

Press P and the whole sky stops where it is. Press it again and everything carries on from exactly there — which is the hard part.

playing

paused — nothing has moved

panels run left to right

Review — last lesson 5 min

Touching a bolt costs a life; the last one sets the state to over.
A collision is tested every frame, so a hurt flag is what stops one touch being sixty.
The cool-down lives in its own script, because a wait in the main loop would freeze the game.

Quick-fire

Last lesson a wait in the wrong place froze the game by accident. Today you want to freeze it on purpose. Is the answer a wait?

Reveal the answer

Almost — it is wait until, which is different. A plain wait stops for a length of time you choose. wait until stops for as long as a condition says so, which is exactly what a pause is.

Today’s Topic 3 min

wait until <(state) = [play]> at the top of every loop
A key that toggles between two states
Pausing clones, and pausing a clock
Making a pause look paused

Learning outcome

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

Stop and restart a whole game with one key.
Find the one script that ignored the pause, by measuring it.
Say why Scratch’s timer is no use to a game that can be paused.

Learnt — stopping, and starting again 28 min

1 · A fourth state, and a key that toggles

Add paused to your states. The key that switches between it and play is a toggle — it asks where it is and goes the other way:


when [p v] key pressed
if <(state) = [play]> then
  set [state v] to [paused]
else
  set [state v] to [play]
end

The same “ask before you act” shape as the space bar in Lesson 3-21. One key, two meanings, no confusion.

2 · One block freezes a script


repeat (40)
  wait until <(state) = [play]>
  next costume
  change x by (8)
  change [ticks v] by (1)
end
say [Forty ticks - however long you held P.] for (2.5) seconds

The loop still runs exactly forty times. Pausing changes how long that takes, not what happens.

WHAT IT SHOULD LOOK LIKE

One block does it. `wait until <state = play>` at the top of the loop parks the script and costs nothing while it waits.

forty ticks, however long you paused

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then press P a few times as the parrot crosses the Stage.

Forty ticks, every run, however long you paused for. That is what resume means.

3 · Every loop, in every sprite

One sprite pausing is not a pause. Every loop that moves anything needs the same block — and that includes the loop inside a clone, because each clone is running its own copy:


when I start as a clone
show
repeat until <(x position) < (-230)>
  wait until <(state) = [play]>
  change x by (-6)
end
delete this clone

A star drifting across the sky. Thirty clones, thirty copies of this loop, thirty waits — and they all stop on the same frame.

WHAT IT SHOULD LOOK LIKE

Three sprites, the same one block each, and the Stage stops together. A clone waits too — the wait goes inside the clone's own loop.

all three asking

Runs here in the page. Nothing to install.

How to use this: Click the green flag, fly with the arrows, then press P. Look at the stars and the bolt, not the parrot.

Three sprites and a crowd of clones, all stopping together.

Basic — press P 24 min

Open last lesson’s Storm Flight. Stars to collect, and a pause that works.

Step 1 — stars to fly through

Add the Star sprite. Under the flag it hides and becomes a spawner.
Its loop: wait until playing, go to the right-hand edge at a random height, clone itself, wait about half a second.
The clone script: show, then drift left until off the edge, then delete.
Inside the drift loop, test touching (Parrot v)? — add a point and delete the clone.

Step 2 — the pause key

Add the toggle script from above to the Parrot.
Count pauses while you are there, so you can prove it fired.

Step 3 — the wait, everywhere

Put wait until <(state) = [play]> at the top of the parrot’s flying loop.
The same at the top of the star spawner’s loop.
The same inside the clone’s drift loop. This one gets forgotten.

Step 4 — the sign

Add a sprite to be your sign — a plain button costume is fine — and put it near the top of the Stage.
Its whole script is a forever loop: if the state is paused, show and say PAUSED - press P; otherwise hide.


when flag clicked
hide
go to x: (0) y: (120)
forever
  if <(state) = [paused]> then
    show
    say [PAUSED - press P]
  else
    hide
    say []
  end
end

The sign never needs telling. It watches the state, like everything else.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, collect a few stars with the arrow keys, then press P. Press P again to carry on.

What you are aiming at. Thirteen stars collected, one pause, and nothing lost across it.

The parrot stops but the stars keep coming.

The star spawner’s loop has no wait, or it has one but the clone’s drift loop does not. Check both.

Pressing P does nothing.

The toggle is checking = against a word that does not match — Paused is not paused here because you typed it twice differently. Copy the word rather than retyping it.

P pauses but will not resume.

You used two if blocks rather than if / else. The first sets the state to paused, and the second immediately sees “paused” and sets it back — so it flickers, or never changes.

The sign appears but nothing else freezes.

The sign is the only script asking. That is Challenge 1 — every other loop needs the wait.

The parrot jumps forward when I resume.

The wait is below the movement rather than at the top of the loop body, so one more step was taken before the pause took hold.

CHALLENGE 1 · L3-23-M1🪙 30 Adcoins8 min

The runaway

Find the script that ignored the pause by measuring it rather than squinting at the Stage.

Give the parrot a tick counter and the bolt a tick counter.
The parrot’s loop waits; the bolt’s does not.
Pause for a few seconds and compare the two numbers.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — one script with a plain forever loop and no wait. The parrot froze at 173 ticks; the bolt sailed on to 241.

paused, and one sprite did not notice

Runs here in the page. Nothing to install.

How to use this: Click the green flag, let it run, press P, and wait. Watch the two counters separate.

Parrot 173, bolt 241. The gap is exactly how long the game was paused for.

Done when: your two counters are equal before the pause and different after it, and you can say which script is the liar.

Teacher note

CHALLENGE 2 · L3-23-M2🪙 50 Adcoins9 min

The clock that will not pause

Put Scratch’s own timer on the Stage next to a clock you keep yourself, and pause the game.

Show the built-in timer readout.
Keep your own my time, changed only while playing.
Pause for several seconds and compare.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — Scratch's own timer runs on real time and pauses for nobody. A clock the game controls has to be a variable you keep yourself.

paused for three seconds

Runs here in the page. Nothing to install.

How to use this: Click the green flag, watch both clocks, then hold the pause for a few seconds.

My time stops dead. The built-in timer does not — it measures real time, not game time.

Done when: the two clocks agree before the pause and disagree afterwards by roughly the length of the pause.

Teacher reveal — and a trap worth showing


forever
  wait until <(state) = [play]>
  wait (0.5) seconds
  change [my time v] by (0.5)
end

CHALLENGE 3 · L3-23-M3🪙 70 Adcoins10 min

A pause that looks paused

Freezing is not enough — a player needs to see that it was deliberate.

Every sprite dims while the game is paused.
The sign appears over the top.
Resuming undoes all of it, with nothing left dim.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a pause that looks paused. Everything dims by the same amount, and resuming undoes all of it.

dimmed

Runs here in the page. Nothing to install.

How to use this: Click the green flag and press P. Everything on the Stage dims together, and brightens on resume.

Brightness −35 on every sprite, cleared on resume. A frozen game without this just looks broken.

Done when: pausing and resuming five times leaves the Stage looking exactly as it started.

Teacher note

EXTRA MISSION · L3-23-MX🪙 100 Adcoinsbonus

Slow motion

Prove your state machine is not just an on/off switch. Add a slow state: the same game, running at a quarter speed.

The S key toggles between play and slow.
The pause still works from either of them.
The flying loop runs in both, with a wait added only in slow.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, press S for slow motion, P to pause, S again to speed up.

A fourth state, and the same loop serving all of them.

Teacher note

Summary 5 min

wait until <(state) = [play]> at the top of a loop body is the whole of pause.
Every loop needs it — including the one inside a clone.
A toggle key uses if / else, not two ifs.
Scratch’s timer measures real time and cannot be paused. Keep your own.
Add 0.1 repeatedly and the number goes wrong. Halves and quarters are exact.
A pause must look paused, and resuming must undo all of it.

Pause: A state in which everything waits, keeping its place.
Toggle: A control that switches between two things each time you use it.
Game time: Time that only passes while the game is being played.
Runaway script: A loop that never asks the state, and so never stops.

Hand in

Save your game. Next lesson finishes the arc: a score, a best that outlives the round, and a menu that adds one more state.