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I'm just starting to play about in Scratch...

I seem to have a sprite of a cat with two 'costumes', which I guess are like frames.

I made this sequence:

enter image description here

...but when I click the green flag the cat moves to the right but the costumes don't switch.

If I make a simpler sequence:

enter image description here

...and manually change the costume in the drop-down then the costume does change.

What is the limitation here?

Anentropic
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2 Answers2

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This is by design. By default, loops have a built-in delay of about 1/30 second. (There are ways to eliminate that delay, but that is off-topic here.) This was done to help inexperienced programmers witness the effect of a loop; possibly also to make execution speed more consistent (regardless of client's CPU power).

In your case, that means costume2 will be visible for 1/30 second before switching back to costume1. Costume1 on the other hand, is instantly followed up by costume2. Consequently, you will only see costume2.

There are various ways to fix that.

  1. Change your script to repeat 5 { move 10 steps; next costume; } This gives both costumes an implicit 1/30 second delay. If this is still too short, add a delay (wait ... seconds). Note: next costume wraps around, so assuming the sprite has 2 costumes, it will flip back and forth between costume1 and costume2.
  2. Too jerky? Use glide ... secs to ... instead of 'move and wait'.
  3. Or just take smaller steps; swap costume once every few steps.
  4. Make two separate scripts running in parallel, one for the movement, the other for switching costumes. That makes it easier to specify a different delay for each.
Ruud Helderman
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  • oh... is my problem that I assumed that "move 10 steps" took some time, i.e. animated the movement... but actually it instantaneously moves 10 pixels, or rather in 1/30s? – Anentropic Feb 11 '22 at 13:40
  • I can imagine the confusion; the documentation is not very explicit on this. Move is instantaneous; most Scratch blocks are. Exceptions are loops (as explained), `wait`, `play sound` and `glide`. The latter will do what you had in mind: move gradually. – Ruud Helderman Feb 11 '22 at 13:52
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Try using a [wait] block: the change between costumes may be so fast that it seems like it is walking without changing costumes...

taylor.2317
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    it seems to just stick on one of them, like the second costume change doesn't happen. inserting the wait does make the costume change happen, but of course adds a stutter to the movement – Anentropic Feb 09 '22 at 21:04
  • I believe it is an error. Are you able to use decimal wait times, e.g. 0.1? – taylor.2317 Feb 09 '22 at 21:06
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    yes, it does seem like a bug maybe. 0.1s looks ok as a compromise. would love to know the root cause, if there's a right way to fix it – Anentropic Feb 09 '22 at 22:18