Scratch

Have you ever made a script do do something, but when you play it, something goes wrong? Then you look at your scripts and you just can't see what's wrong. It should work perfectly. But it doesn't. Here, I've collected the most common problems I encounter when making a script, and I'll tell you how to get around these problems.

Delays
These blocks can cause delays in scripts.

wait 
 
 secs

wait until 
 

repeat until 
 

play sound 
. ▼
 until done

say 
 
 for 
 
 secs

think 
 
 for 
 
 secs

glide 
 
 secs to x: 
 
 y: 
 

When these are used, the ENTIRE script will be held up until these actions are completed. For example:

when  clicked
forever
if 
key 
up arrow ▼
 pressed?
next costume
wait 
0.2
 secs
if 
key 
right arrow ▼
 pressed?
change x by 
5

In this script, the right arrow is used to move.
If the Up Key is pressed, the sprite will change costumes making an animation. There will be a short pause between each costume change so that the animation is visible.

However, the 0.2 second wait will affect the entire script. This means that while the animation is running, the sprite will be unable to move until the 0.2 seconds are up. This will make movement jolty. (I know this isn't the best example, but I hope you see what I mean)

HOW TO FIX THIS
The simplest way is to break this into 2 separate scripts. So the above script would become

when  clicked
forever
if 
key 
up arrow ▼
 pressed?
next costume
wait 
0.2
 secs
when  clicked
forever
if 
key 
right arrow ▼
 pressed?
change x by 
5

This is why 1s1s projects are exceptionally impressive.

Double-Scripting
This is when you include 2 contradicting blocks. For example, in the same sprite you might include

change 
variable ▼
 by 
10

and

set 
variable ▼
 to 
100

It might seem at first that this sort of stuff will never happen, and very few people do this, but actually, this is one of the most common problems I've seen. You could forget that you put one of those blocks there and forgot to remove it.

TO FIX THIS you just have to carefully double-check every sprite in you project if it's a "For every Sprite" variable or just for the subject sprite if it's a "For this sprite only" variable. NOTE: I only talk about variables but the same thing applies to the

change x by 
5

and the

set x to 
5

Colour Sensing
this applies to the blocks,

touching color 
?

and

color 
 is touching 
?

If sensing isn't working, all I can say is double-check you have the right colours. Be careful if you use the effect blocks

change 
color ▼
 effect by 
5

change 
brightness ▼
 effect by 
5

change 
ghost ▼
 effect by 
5

as you would need to adjust the colours in the sensing blocks to match this. You can use this block to reset the effects:

clear graphic effects

Where possible, use the block

touching 
sprite1 ▼
?

Using the = Sign
Look at this platformer script:

forever
if 
touching 
star ▼
?
change 
score ▼
 by 
5
if 
touching 
coin ▼
?
change 
score ▼
 by 
1
if 
score
=
100
say 
You Win!!!

So you play the game, collecting stars and coins but the sprite never says that you win. You look at the score and it's 126, so surely you've won by now and the sprite should say so. But no. Because the sprite will only say so if score=100 but score never did =100. You could have gotten 6 coins and then gotten 24 stars, meaning that the score was 96, then 101 but never 100 itself. See the problem?

TO FIX THIS use this block instead.

if 
score
 > 
99
say 
You Win!!!

Pen not working?
The pen only draws on the background so if there's a sprite in the way, the pen markings will only show underneath the sprite, on the background. There's no real way to fix this, but at least you know what the problem is.

I hope I've explained things clearly and if there are any other common problems or glitches, tell me 

Last edited by PhirripSyrrip (2012-06-11 16:07:29)