(Redirected from Procedure)

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define custom block
The Define block
define custom block
The Define block in Scratch 2.0
Past versions of the Define block

My Blocks (known as More Blocks in Scratch 2.0) is one of the ten categories of Scratch blocks. It holds procedures for the selected sprite. They are color-coded pink. Before any blocks are created, it is empty, except for a "Make a Block" button.

Clicking Make a Block brings up a dialogue allowing the user to make a procedure. Once OK is pressed, the new block appears in the palette and an empty definition appears in the code area. When the procedure runs, Scratch will run the blocks below the corresponding Define block.

Uses of My Blocks

Apart from variables, procedures are the main kind of abstraction used in procedural programming; they let Scratchers write scripts without knowing or thinking about the details of what each script does. This is also true of Scratch's primitive blocks, like move () steps. For example, suppose one wants a sprite to vanish and reappear. To vanish, the sprite should play a sound and repeatedly increase the ghost effect; to reappear, it should repeatedly decrease the ghost effect. This should happen at several points in the project. Without procedures, the Scratcher would have to duplicate the same sequence of blocks at each point, but by making "vanish" and "appear" blocks, they can write scripts in a way which matches how they think of them:

. . .
think [Hmm...] for (2) secs
vanish
. . .
appear
play sound [Horse v] until done
. . .

define vanish
start sound [Ripples v]
repeat (10)
    change [ghost v] effect by (10)
end

define appear
repeat (10)
    change [ghost v] effect by (-10)
end
The Make a Block dialog

Now, if the user changes their mind about how the sprite should vanish or appear, they need only change the block definitions.

Custom blocks also help by reducing project file size and allowing the user to disable screen refresh. Number, string, and Boolean inputs can be added to custom blocks. For example, a Scratcher could make a jump () :: custom block with a "height" input, and (height :: custom-arg) will appear in the Define block. These blocks can be dragged out and used in the definition just like variables.

Run without screen refresh

Using custom blocks is the only way to run scripts without screen refresh. Screen refresh is the very minuscule wait which occurs at the end of each iteration of a loop block or when a block which waits is used. The Make a Block dialog offers to disable screen refresh (by default it is enabled.) This can make it less obvious what is happening, but is useful if one wants to make changes without the user seeing the intermediate steps or waiting a long time. For example, if one uses this script:

set [i v] to [0]
pen down
repeat (200)
    move (i) steps
    turn cw (92) degrees
    change [i v] by (1)
end
pen up

the user may watch the sprite drawing the picture. But if one places it in a custom block with screen refresh disabled, the user will only see the complete picture, and it will finish much sooner.

Workaround

Main article: List of Block Workarounds

In most simple cases, custom blocks can be worked around by using broadcasts and variables. However, this does not allow recursion, disabling screen refresh, or for multiple scripts to use the same procedure at the same time.

when gf clicked
broadcast [jump v] and wait

when I receive [jump v]
repeat (5)
    change y by (6)
end
repeat (5)
    change y by (-6)
end

Procedures in Snap!

Snap!, previously called BYOB, is a graphical programming language based on Scratch. Among other things (the most important of which are first class procedures and first class lists) Snap! allows making reporters and predicates as well as stack blocks.

Common Suggestions

Document.png Please expand this article or section. You can help by adding more information if you are an editor. More information might be found in a section of the talk page. (April 2019)

Many Scratchers would like the ability to make custom reporter and boolean blocks.[1] Additionally, dropdown inputs as arguments have also been requested, to the extent that some people used JSON hacking to insert them into custom blocks (though this does not work in Scratch 3.0.)

References

  1. AonymousGuy. (10/11/2013). "CUSTOM REPORTER BLOCKS[suggestion]" topic:20661