Next Costume Animation

Learning Goals 3 min

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

1. Use next costume and explain what happens at the end of the list.
2. Rebuild a walk cycle with fewer blocks than before.
3. Animate a sprite whose costume names you have never looked at.

Warm-Up 7 min

Your walk cycle works, but look at the cost. Six blocks inside the loop, two of them just naming costumes — and it only works for a sprite with exactly two poses, called exactly those names.

Quick-fire puzzle

Wei Jie replaced his two costume blocks with one he had never used before. It still worked. What does this block do?

when flag clicked
repeat (8)
  next costume
  wait (0.2) seconds
end
        

New Concept — stepping through the list 15 min

Think of the costume list as a ring rather than a line. next costume takes one step round the ring, and after the last costume the next step brings you back to the first.

Blocks reference

Why the wrap-around matters

With two costumes, wrapping produces a perfect alternation and you barely notice it. With four, you get a proper four-frame cycle. With one, the block does nothing at all — there is nowhere to step to.

When to use which

In practice the two work together: a switch at the top of a script to guarantee a known starting pose, then next costume inside the loop to do the animating.

Why it matters

Animation stops being something you build laboriously for one sprite and becomes something you can add to any sprite in two blocks. That difference decides whether you bother.

Worked Example — the same walk, half the blocks 15 min

We rebuild last lesson’s walk cycle, then use the spare blocks for something the old version had no room for.

Step 1 — Count the old version

Look at last lesson’s walk. Eight blocks, six of them inside the loop, and two of those six exist only to name costumes.

Step 2 — Replace the pair with one block

Delete both switch blocks from inside the loop and drop in a single next costume.

when flag clicked
go to x: (-160) y: (0)
repeat (8)
  next costume
  move (40) steps
  wait (0.2) seconds
end
        

Step 3 — Run them side by side

Genuinely identical. All you have removed is the part where you told Scratch something it could work out for itself.

Step 4 — Guarantee a clean start

There is one thing the old version had by accident: a known starting pose. Add a switch above the loop to get it back deliberately.

when flag clicked
go to x: (-160) y: (0)
switch costume to [costume1 v]
repeat (8)
  next costume
  move (40) steps
  wait (0.2) seconds
end
        

Step 5 — Spend the block you saved

You are still a block under the cap, so add a line of dialogue at the end — something the old eight-block version had no room for at all.

Step 6 — Try it on a sprite with more costumes

Select Abby, who has four costumes rather than two, and give her the same loop. It works immediately, cycling all four. The old named-costume approach would have needed four blocks and four correct names.

That is the real argument for this block. It is not that it saves two blocks on the cat — it is that it works on any sprite without you knowing anything about it.

What changed: animating a sprite went from a chore worth avoiding to two blocks you can add to anything.

The full assembled stack (your reference)

when flag clicked
go to x: (-160) y: (0)
switch costume to [costume1 v]
repeat (8)
  next costume
  move (40) steps
  wait (0.2) seconds
end
say [Made it!] for (2) seconds
        

Try It Yourself — three small builds 12 min

when flag clicked
repeat (10)
  next costume
  wait (0.15) seconds
end
        

when flag clicked
repeat (12)
  next costume
  wait (0.2) seconds
end
          

Mini-Challenge — animate a stranger 5 min

“A sprite you have never met”

Add any sprite from the library that you have not used before, and animate it — without opening its Costumes tab first.

It works if:

• One flag click animates the new sprite.
• You wrote the script before checking how many costumes it has.
• The animation reads as movement rather than a random flicker.
• You can say afterwards how many costumes it turned out to have, from watching alone.

when flag clicked
repeat (12)
  next costume
  wait (0.2) seconds
end
        

Recap 2 min

The costume list is a ring. next costume takes one step round it and wraps from the last back to the first, which means it needs no names and no knowledge of how many costumes there are. Pair it with a switch above the loop when you need a known starting or finishing pose. It works on any sprite, which is what makes animation something you will actually use.

next costume

A Looks block that steps to the following costume, wrapping round after the last.

Costume ring

The way the costume list behaves — after the last one, back to the first.

Animation cycle

One complete pass through all of a sprite’s costumes.

Starting pose

The costume a sprite is set to before an animation begins, so runs look identical.

Homework 1 min

Two sprites, two speeds. Animate two different sprites side by side and give each one a pace that suits it.

1. Put the cat and one other sprite on the Stage.
2. Give each an animated walk using next costume.
3. Tune the two wait times so the sprites feel like different creatures.
4. Screenshot both Script Areas and note your two wait values.

when flag clicked
switch costume to [costume1 v]
repeat (8)
  next costume
  move (30) steps
  wait (0.2) seconds
end
        

Bring back next class:

• Your screenshots and your two wait values.
• Your answer to: “Why does the same script animate a two-costume sprite and a four-costume sprite without any changes?”

Heads up for next class: SCR-L01-28 teaches size — how to make a sprite grow, shrink, and come back to normal.