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This article will need to be updated upon the release of Scratch 3.0. If you are an editor, please update this when Scratch 3.0 is released. If you are an editor, please create the post-3.0 version at Scratch Wiki:3.0 Articles/Encoding and Decoding Cloud Data. There may already be ongoing discussion about how to do so on its talk page. What needs to be updated: Scratch 3.0 will have limitations |
Encoding a cloud variable is the process where one takes a list, or a string, and compiles it into a number-only format in a cloud variable. The reason for this, is because Scratch currently only supports numbers in a cloud variable due to their storage limitations. Numbers take up way less space and is easier to process in the Scratch data base. It can be used for creating large online leader-boards or even massive multiplayer online games.
Contents
Quick Method
Variables/Lists Needed
This method will assume several variables. These are:
- z
- i
- i2
- i3
- ☁ data
- C
One list, named "users", will also be used.
In this example, the project will keep track of users who visit it. However, it is trivial to replace the users list with something else. Alternately, the list and repeat blocks can be removed to only encode a single variable.
Encoding
The encoding process takes each item in a list, separates them with a particular number, and converts each letter into a number with a fixed amount of digits.
This project assumes that it separates them with the code 00. The code 00 is used in the following script to separate list items because no character in the variable "z" has an indexed position of 0. In simpler terms, when the cloud variable is encoded, each letter of each item of the list is added as a number. The number represents the letter in the variable "z" (which lists all characters) by which the character from the list meets its equivalent position.
For example, if the first letter of the encoding process is "b", the code representing "b" would be 12 because the twelfth letter of the variable "z" is "b". The variable that contains all the letters used for parsing is named "z" because each time the variable's value is called, a shorter name takes up less processing power to report the specified character.
when gf clicked
set [z v] to [0123456789abcdefghijklmnopqrstuvwxyz?] //the variable name is kept short for faster script execution
define encode
set [i v] to [0]
set [C v] to []
repeat (length of [users v])
change [i v] by (1)
set [i2 v] to [0]
repeat (length of (item (i) of [users v]))
change [i2 v] by (1)
set [i3 v] to [0]
repeat until <<(letter (i2) of (item (i) of [users v])) = (letter (i3) of (z))> or <not <(i3) < (length of (z))>>>//if the letter is not included in the variable "z" the loop will not end, so it stops once it's reached the last letter of z
change [i3 v] by (1)
end
if <(length of (i3)) < (length of (length of (z)))> then //If the number of digits in i3 is less than the maximum possible number of digits, prepend 0s until the length is equal
repeat until <not <(length of (i3)) < (length of (length of (z)))>>
set [i3 v] to (join [0] (i3))
end
end
set [C v] to (join (C) (i3))
end
repeat (length of (length of (z)))
set [C v] to (join (C) [0])
end
end
set [☁ data v] to (C)
Decoding
Decoding takes the encoded number data and compiles a list out of it. Modifications must be made with the encoder and decoder if multiple lists need to be compiled for a project's particular purposes.
define decode
set [i v] to [0]
set [i3 v] to []
set [C v] to (☁ data)// to avoid getting the value of cloud data too much
delete (all v) of [users v]
if <not <((length of (C)) mod (length of (length of (z)))) = [0]>> then
repeat until <((length of (C)) mod (length of (length of (z)))) = [0]>
set [C v] to (join [0] (C))
end
end
repeat ((length of (C)) / (length of (length of (z))))
set [i2 v] to []
repeat (length of (length of (z)))
set [i2 v] to (join (i2) (letter ((i) + (length of (i2))) of (C)))
end
if <(i2) = [0]> then// 000 = 0 is true, so no matter how long the 0 is it'll be true here
add (i3) to [users v]
set [i3 v] to []
else
set [i3 v] to (join (i3) (letter (i2) of (z)))
end
change [i v] by (length of (length of (z)))
end
In-Depth Method
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Warning
This method requires a few edited blocks which can be obtained by editing the JSON of a Scratch project, so if done wrong it can render the project unopenable. Use the above method or make a backup of the project if you don't feel safe editing the project's JSON.
Variables/Lists Needed
This method uses a script to create most the variables required, it should look something like this:
define Create Vars
set [Characters v] to [� !"#$%&'()*+,-./:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\\]^_`abcdefghijklmnopqrstuvwxyz{|}~0123456789]
set [p1 v] to [1] //This variable is the ID that will be given to the character
repeat (length of (Characters))
set (letter (p1) of (Characters)) to (join([floor v] of ((p1)/(10)))(round((p1) mod (10))))//This edited block creates a variable with the name of a specific character, with that character's 2 digit number ID inside the variable
change [p1 v] by (1)
Additional variables that must be manually created include:
- Characters
- p1
- p2
- p3
- p4
- ☁ data
Lists include:
- CloudList
- bypass
- hold
Encoding
The encoding process works in the same way as the above method, although this method uses a faster way of encoding characters to their 2 digit ID number that includes another edited block:
define Encode
delete (all v) of [bypass v]
set [p1 v] to [1]
repeat (length of [CloudList v])
set [p2 v] to [1]
set [p3 v] to (item (p1) of [CloudList v])//sets a variable to the item of the cloud list we are currently encoding
repeat (length of (p3))
set [p4 v] to (join ((letter (p2) of (p3)) of [Sprite1 v])[1])//This edited block is used to pull the data out of those variables you set with "Create Vars" replace Sprite1 with the sprite that ran the Create Vars custom block
add (letter (1) of (p4)) to [bypass v]
add (letter (2) of (p4)) to [bypass v]//Adds the 2 digit ID of the character to the list
change [p2 v] by (1)//changes to the next character in the item of the cloud list so it can encode it
end
add [0] to [bypass v]
add [0] to [bypass v]//These 0s tell the decoder to make a new item
change [p1 v] by (1)//changes to the next item in the cloud list so it can encode it
end
set [☁ data v] to (bypass)//The bypass list is used to bypass the 10240 character limit of the join block, it also prevents cloud flooding (setting a cloud variable more than 3 times a second)
Decoding
The decoding script for this method will look very similar to the script for the easier version. Luckily, there are no edited blocks in this script!
define Decode
set [p1 v] to [1]
set [p2 v] to [2]
delete (all v) of [CloudList v]
delete (all v) of [hold v] //This list collects the data for one item of the Cloudlist, it is then added to the CloudList and the process is repeated
repeat ((length of (☁ data)) / (2))//Since we encoded each character into a 2 digit number, they must be decoded in sets of 2 digits
set [p3 v] to (join (letter (p1) of (☁ data)) (letter (p2) of (☁ data)))//Uses two variables (p1 and p2) for speed, since using another variable is faster than using (p1+1)
change [p1 v] by (2)
change [p2 v] by (2)
if <(p3) = [0]> then//Doesn't need to be 00, because according to scratch, 00 = 0 even when they are read as strings
add (hold) to [CloudList v]//adds decoded data to the cloud list in one item
delete (all v) of [hold v]//deletes and repeats
else
add (letter (p3) of (Characters)) to [hold v]//collects decoded data
end
end
