Firework Show I

Review — the Card Battle arc 5 min

• Linear search walks a list until it finds what it wants.
• Bubble sort swaps neighbours until a pass goes by with nothing to swap.
• A swap needs a third box — and lists in step are swapped together.

Quick-fire

Your bubble sort’s nine-block swap appears in three different scripts. You find a bug in it. How many places do you have to fix?

Today’s Topic 3 min

• My Blocks — making a block of your own
• define launch — the hat that holds the work
• Calling it, as many times as you like
• A block that calls another block

Learning outcome

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

1. Make a block and put a stack inside it.
2. Call your own block from a script.
3. Say why one definition beats three copies.

Learnt — giving a stack a name 28 min

1 · One firework is eight blocks

Here is a firework: a rocket appears at the bottom, glides up, hides, and leaves a burst of clones behind it.

show
set size to (45) %
go to x: (0) y: (-170)
glide (0.4) secs to x: (0) y: (90)
hide
repeat (14)
  create clone of [myself v]
end
            

Now you want three. So you copy it, twice. And now:

• The script is twenty-four blocks and runs off the bottom of the screen.
• To make the bursts bigger you change three numbers, in three places.
• If you miss one, two fireworks are big and one is not, and you will not notice.

2 · Make a Block

1. Scroll to the bottom of the block palette and click My Blocks.
2. Click Make a Block.
3. Type launch as the name and click OK.
4. A pink define launch hat appears in your code area.
5. A pink launch :: custom block appears in the palette.

define launch
show
set size to (45) %
go to x: (0) y: (-170)
glide (0.4) secs to x: (0) y: (90)
hide
repeat (14)
  create clone of [myself v]
end
            

3 · Calling it

Now the green-flag script says what happens, not how. Three calls, three fireworks:

when flag clicked
launch :: custom
wait (0.9) seconds
launch :: custom
wait (0.9) seconds
launch :: custom
            

4 · The definition is the one true copy

Change repeat (14) to repeat (30) inside the define hat. Every firework in the show gets bigger, because there is only one place the burst size lives.

Basic — a show made of calls 24 min

Start a new project. A night backdrop and one star sprite is all you need.

Step 1 — the spark

1. Add when I start as a clone.
2. Under it: show, set size to (35) %, point in direction (pick random (-180) to (180)).
3. Then repeat (12) holding move (pick random (6) to (14)) steps and change [ghost v] effect by (8).
4. Finish with delete this clone.

Step 2 — one firework

1. Build the seven-block rocket stack from the Learnt.
2. Put it under the green flag and check you get a burst.

Step 3 — make the block

1. My Blocks → Make a Block → call it launch.
2. Drag your rocket stack out from under the flag and under the define hat.
3. Put one launch :: custom under the flag instead.
4. Run it. It should be exactly as it was.

Step 4 — a show

1. Put repeat (5) under the flag.
2. Inside it: launch :: custom and wait (0.7) seconds.

Step 5 — make each one different

1. Inside the definition, change the go-to and glide x to (pick random (-160) to (160)).
2. Change the glide y to (pick random (40) to (120)).
3. Run it. Five fireworks, all over the sky, from one block.

define launch
change [fireworks v] by (1)
show
set size to (45) %
go to x: (pick random (-160) to (160)) y: (-170)
glide (0.4) secs to x: (x position) y: (pick random (40) to (120))
hide
repeat (16)
  create clone of [myself v]
end

when flag clicked
set [fireworks v] to (0)
repeat (5)
  launch :: custom
  wait (0.7) seconds
end
            

A second block

One block is a habit. Two is a vocabulary.

• Make a second block called finale that fires three at once.
• The script is: launch, launch, finale.
• Somebody reading your script can tell what the show does without running it.

A block inside a block

Your blocks can use each other.

• A volley block that calls launch three times.
• The script calls volley twice.
• Six fireworks, and the word “launch” appears once in your whole project.

define volley
launch :: custom
wait (0.35) seconds
launch :: custom
wait (0.35) seconds
launch :: custom
            

One edit, every firework

Prove the payoff. Change the show without touching the script.

• Double the number of sparks in every firework.
• You may change exactly one number.
• You may not touch the green-flag script at all.

Give the show an opening

A firework show starts with a countdown. Make that a block too, and your script becomes a running order.

• A count down block that shows 3, 2, 1, GO!
• The script is: count down, then four launches.
• The countdown is big and readable, and the rocket is not.

define count down
show
go to x: (0) y: (0)
set size to (90) %
set [count v] to (3)
repeat (3)
  say (count) for (0.7) seconds
  change [count v] by (-1)
end
say [GO!] for (0.7) seconds
hide
            

Summary 5 min

• My Blocks → Make a Block gives you a block of your own.
• The work goes under the define launch hat. A definition does not run by itself.
• The script calls it, as many times as you like.
• One definition means one place to fix, and one place to improve.
• A block can call another block. Name each one for what it does.

My Block

A block you make yourself, holding a stack you name.

Define

The pink hat that holds a My Block’s blocks.

Call

Using your block in a script.

Definition

The one place a My Block’s work actually lives.

Hand in

Save your show. Next lesson your block learns to take instructions — where to fire, how high, and how big the burst should be.