Firework Show II

Review — where we got to 5 min

• define launch holds the work; the script calls it.
• One definition means one place to change.
• A block can call another block.

Quick-fire

Your launch block fires in a random place. You want one exactly in the middle, for the finale. What can you do about it right now?

Today’s Topic 3 min

• Inputs — adding a slot to your own block
• define launch (x) (height) (sparks)
• Reading an input inside the definition
• One block that makes every firework in the show

Learning outcome

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

1. Add number inputs to a My Block.
2. Use an input inside the definition, including in a sum.
3. Write a show as a list of calls with different numbers.

Learnt — telling your block what to do 28 min

1 · Adding an input

1. Right-click your define launch hat and choose Edit.
2. Click Add an input: number or text.
3. Type x over the name it suggests.
4. Click OK.
5. The hat now reads define launch at (x), with an orange oval in it.

That orange oval is the input. Drag a copy of it out of the hat and into the go-to block, and the block will use whatever number the call gives it:

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

when flag clicked
launch at (-150) :: custom
wait (0.7) seconds
launch at (0) :: custom
wait (0.7) seconds
launch at (150) :: custom
            

2 · Three inputs

Add two more the same way — height and sparks — and the block can make any firework you can describe:

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

launch (-140) (50) (8) :: custom
              

launch (0) (120) (26) :: custom
              

3 · The order of the slots matters

launch (0) (120) (26) :: custom means x 0, height 120, sparks 26. Swap two numbers and you get a firework 26 pixels up with 120 sparks in it — which is a mess, and Scratch will not warn you.

Basic — a written show 24 min

Open your show from last lesson.

Step 1 — add the inputs

1. Right-click the define hat, Edit, and add three number inputs.
2. Call them x, height and sparks.

Step 2 — use them

1. Drag the x oval into both the go-to and the glide.
2. Drag the height oval into the glide’s y.
3. Drag the sparks oval into the repeat.
4. Take out the pick-random blocks you had there.

Step 3 — write the show

1. Delete the repeat loop under the green flag.
2. Put five calls there instead, one per firework.
3. Give them numbers that build: low at the edges, high in the middle.

Step 4 — pace it

1. Put wait (0.5) seconds between the calls.
2. Try 0.2 and 1.2 as well, and pick the one that looks best.

Step 5 — read it back

1. Look at your script without running it.
2. Can you tell what the show looks like? If not, the numbers need comments.

when flag clicked
launch (-160) (60) (10) :: custom
wait (0.5) seconds
launch (-80) (100) (16) :: custom
wait (0.5) seconds
launch (0) (140) (30) :: custom
wait (0.5) seconds
launch (80) (100) (16) :: custom
wait (0.5) seconds
launch (160) (60) (10) :: custom
            

A different sky every time

Put random numbers in the call rather than in the definition.

• Six fireworks, all in random places, at random heights, in random sizes.
• The definition has no pick-random in it at all.
• Press the flag twice and get two different shows.

Colour it

A fourth input: what colour the sparks should be.

• define launch (x) (height) (sparks) (colour)
• Three fireworks in three obviously different colours.
• The sparks get the colour, not just the rocket.

define launch (x) (height) (sparks) (colour)
set [shade v] to (colour)
...

when I start as a clone
set [color v] effect to (shade)
            

One input, two jobs

Make the higher fireworks automatically bigger, with one fewer input.

• Take the sparks input away.
• Work the burst size out from the height instead.
• A low firework is small, a high one is big, and the show looks better for it.

define launch (x) (height)
...
repeat ((height) / (6))
  create clone of [myself v]
end
            

A wave across the sky

Seven fireworks that walk from the left edge to the right, each one a little higher than the last — from one loop and one block.

• A counter that goes 1 to 7.
• The x and the height are worked out from the counter.
• You wrote one call, not seven.

set [n v] to (0)
repeat (7)
  change [n v] by (1)
  launch ((-210) + ((n) * (52))) ((50) + ((n) * (10))) (12) :: custom
  wait (0.35) seconds
end
            

Summary 5 min

• Edit a My Block to add inputs: define launch (x) (height) (sparks).
• The orange ovals in the hat are dragged into the body to be used.
• An input can go anywhere a number can — including inside a repeat or a sum.
• An input only exists inside its own definition. To reach a clone script, copy it into a variable.
• The order of the slots is the order of the inputs, and nothing warns you.

Input

A slot on your block that the call fills in.

Argument

The value handed over in that slot.

Parameter

The orange oval inside the definition that receives it.

Reusable

One block that does a whole family of jobs.

Hand in

Save your show. Next lesson you meet the tickbox at the bottom of the Make a Block window — the one that turns a burst from a dribble into a bang.