Scratch

So tutorials have to be text not a project?

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My name is GP1 and I'm going to show you how to use selector (#selectorNmae) code in Scratch.
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Simple codes
Simple codes
Here is an example of a selector code. I will explain it slowly after we read it.

moveSteps
| t1 t2 t3 |
t1 _ self ownerThatIsA: ScratchSpriteMorph.
t2 _ t1 xpos.
t3 _ t2+10;
t1 xpos: t3

This code will move the current sprite 10 steps.
Okay. Lets go through this now.
the moveSteps is the selector. It is called when another script does self or a menu has

t2 add: 'move current srite 10 steps' action: #moveSteps

Did you know?
self is a way to execute a selector in the same class. If a self is called with a selector afterwards in scratch-ui-panes,  then it will look for it in scratch-ui-panes only. The only way it looks for it in another class is if a variable is a world variable. We'll talk about these later.

Did you know?
a selector is a fancy way of giving a code a name. Like somebody giving their baby a name, then when their older, and they recognize their name, when you call it, they'll come to you (I hope)

the next thing is the temporary variables. These are defined in a pipe (|) and stop difining in another pipe(|). In this example, there are three temporary variables. the first is t1, the second is t2, and the third is t3. You can have as many temporary variables as you want in a code.
Next is a little different. first we call t1, then we are going to tell squeak that we are going to give it a value, wich is _. when you type _, it will turn into an arrow that points left. Don''t be alarmed by it. We are going to make it a global variable so that we can access all the blocks in scratch. We do this by calling self, then use ownerThatIsA: ScratchSpriteMorph. to tell it that the code we want is in scratchframemorph. usually, blocks are located in ScriptableScratchMorph, but motion blocks are only executed as a sprite (the stage can't move). Now that t1 is a global variable, it acts like a self exept only for the class that you assigned it to (ScratchSpriteMorph). We will further call t1 instead of self for this code.

Did you know?
the period is needed at the end of every statement to execute it. It is sort of like a seperator in a binder. You don't need a period at the end of the last statement, though.

We will now call t2 to set a value to it. in scratch, the x position block is called xpos in the browser, so we will use _ to set the value of t2 to that position. We will first (after _) use t1 to call xpos. This will be:

t2 _ t1 xpos.

next, we will set t3. This code moves the current selected sprite 10 steps, so we will give this variable the x position of the sprite moved 10 pixels (steps) to the right. We will call it, the use _ to assign the value to it. the first value we want is t2, thenwe want to add 10 to it. In math (yes, you should have stayed awake) you use + to add two numeric values together. So, we will add 10 to t2 by doing

t2+10.

Did you know?
There are four different math symbols:
/ devides (t1/t2)
* multiplies (t1*t2)
+ adds (t1+t2);
- subtracs (t1-t2)
But, if you want to add two variables of text together (or a variable and some text) the you use ,
example:

Code:

t2 _ 'world!'.
t1 = 'Hello ', t2.

will give t1 the value of "Hello World!"

Finally, we set the x position of the current sprite to t3. First, we call the global variable (t1) then xpos: t3.

Did you know?
xpos and xpos: are two different things. xpos sets a value and xpos: expects the value of wich to set the x position of the sprite. You could set a numeric value to xpos:, but it would count as a string, wich is inside of a pair of ', so it would be xpos: '0'.

There you have your first scratch frame morph code. Keep reading for more info and how to do more things.
I am sorry, I don't have scratch 1.4 on tis computer at this time. I will make the other parts of this tutorial later when I have it for reference.

Last edited by GP1 (2011-07-31 21:12:15)

yes I fixed the old one

ProgrammingFreak wrote:

Glad I could help! 

Thanks!!
Thank you too, GP1!!

bump... Someone please write

GP1 wrote:

  does it have to be related to scratch (ex. Scratch, squeak) or can I do something else, say XNA or html5?

It has to be scratch. But it can be using scratch blocks, like a tutorial on how to scroll.

i'll make another one soon.