# Creators: Spirograph

This week in the Creators group we looked at emulating the classic toy, the Spirograph.

The Spirograph consists of geared plastic discs. One disc is fixed in place over a sheet of paper and the other, with a pencil tracing the path, is allowed to spin around it. The result is a complex and beautiful design on the paper.

This diagram should help explain in conjunction with the photo. The centre of the black disc spins around the centre of the red disc, which itself doesn’t move. So the centre of the black disc rotates around in a circle. Pretty simple?

Now, the pencil itself rotates around the centre of the black disc. Shouldn’t that make a circle too? Well it would if the black disc wasn’t moving. Thankfully though, it is and that’s what makes this interesting.

Finding the Location of the “Pencil”

So how do we find the location of the pencil? Let’s look at our diagram again, but with things re-labeled a bit:

• Centre: Formerly “centre of red disc”. It’s the fixed centre of our spirograph
• Centre2: Formerly “centre of black disk”
• Point: The point on our curve. This is where the pencil would be in a physical spirograph.
• Radius0: Distance from Centre to Centre2
• Radius1:Distance from Centre2 to Point
• Angle0: The current angle of the line between Centre and Centre2
• Speed0: The amount that angle0 increases every time we draw
• Angle1: The current angle of the line between Centre2 and Point
• Speed1: The amount that angle1 increases each time we draw

So at any time the location of our point is:

Point = Centre + [Centre2 relative to Centre] + [Point relative to Centre2]

So know where Centre is and if we can calculate where Centre2 is relative to Centre and similarly where Point is relative to Centre2, we can just add them all together!

Given an angle and a distance, can we get a location?

The answer to this is a resounding “yes”! Look at the diagram:

given an angle and a radius, we can calculate the X and Y position of any point around a circle. The magic is the COS and SIN (pronounced “kos” and “sign”) functions. These functions exist in almost all programming languages and JavaScript’s no exception.

Using p5.Vector

The last big concept we tackled thus week was using P5js’s built-in vector class to store (x, y) points and make our code tidier. To make a vector we just use createVector(x, y). We can then use functions to add them together, etc. We would get the same result working with the X and Y values separately but the code is a lot neater and shorter.

And in conclusion

This looks pretty cool:

Getting this week’s code

As aways, all the code from our Creator group can be found on our GitHub repository.

# Creators: Crawlers with a talent for Art

What did we do? This week in the Creators, our code was full of bugs, but that was okay :)!  We created another project with classes and lists, this time creating an insect-like creature with a very simple mind – … Continue reading

# Creators – Being Random

This week we mainly looked at three things:

• How data is organised on your computer
• Creating functions
• Using randomness to make things interesting

Data Organisation

Most of us had heard of a hard-disk before. This is a stack of metal disks inside your computer. Each metal disk has a special coating made of millions of tiny magnets (like you might find stuck to the fridge) that can be turned on and off.

We saw that able to turn something on and off, like a switch, was enough to count from zero to one, but the more switches we added, the higher we could count. Two switches can count from zero to three:

```Switch 1          | Switch 2          | Total (Add)
[Off = 0, On = 1] | [Off = 0, On = 2] |
------------------+-------------------+-----------
Off = 0           | Off = 0           | 0
On  = 1           | Off = 0           | 1
Off = 0           | On  = 2           | 2
On  = 1           | On  = 2           | 3```

With enough of these tiny switches, we can store anything we need. Each of these tiny switches is also known as a ‘bit’ and a 1 terabyte hard disk has a billion of them!

We also saw that the files on your disk are arranged with folders (also known as directories). Folders can contain both files and more folders. This allow us to keep our hard disk organised; without them all our files would be in the same place which would be difficult once we had more than a few. The location of a file is called its “path”. Looking at the highlighted file on the desktop of my Mac we can see the full path would be:

`/Users/kierancoughlan/Desktop/Ball and Bat Sounds.m4a`

This means that, reading backwards, the file called ‘Bat and Ball Sounds.m4a’ is in a folder called ‘Desktop’ which is itself inside a folder called ‘kierancoughlan’ which is, at the highest level, inside a folder called ‘Users’.

Functions

A function is a collection of commands that do a job together. We’ve already encountered them, even if you hadn’t especially noticed:

• Our P5 template already contains two functions called start() and draw()
• All of the P5 commands we have used, such as createCanvas() and rect() are functions themselves

We could add all our code to start() and draw(), in fact, that’s what we’ve done before this week. That’s fine starting out, but it does mean, once there are a lot of commands in those functions, that our code is gets harder to read and understand. Breaking out a few commands into a new function and giving it a name that describes what it is doing, really helps.

Once we’ve written a function, it can be called as many times, and from as many places, we as need.

Functions can do one other thing too: they can give back a value to the place where they were called from. For this we use the special word return. For example, let’s see what a function to pick the largest of two numbers, we’ll call it Max(), might look like:

```function start(){
let a = 4;
let b = 10;
let c = Max(a, b);
}

function Max(n1, n2){
if (n1 > n2)
return n1;
else
return n2;
}```

We give Max() the two numbers we are comparing. If the first one is bigger than the second, it gives back the first. Otherwise, if gives back the second. Note too that the names of the variables in Max() are different to those in start(), and that’s not a problem.

Random

Finally, we looked at the P5 function random(). We used it two different ways:

```random(); // gives a number between 0...1
random(n); // gives a number between 0...n (where n is a number!)```

In the first form, we used it to pick a random colour. In the second, we used it to pick a random position for our squares.

Files

As usual, all the code is on the creators github repository. Head there and download it!! The files for this week contain both the script we wrote (sketch.js) and a longer version that I wrote (sketch2.js). Feel free to take a look at both!