Creators: Shootah Part 6 – Enemy Shooting Back

alien

This week we did our last iteration on Shootah and added a Bomb to be dropped by the enemy to try to hit the player.

Bomb Class

We copied the existing Bullet class and called it Bomb instead. The main changes we had to make were:

  1. Changing the speed to a negative number so that it moved down instead of moving up (as the Bullet does)
  2. Changed the check for the top of the screen to one for the bottom of the screen instead (to account for the fact it moves down)
  3. Changed the check in its hit() function so that the Bomb doesn’t interact with the Enemy when it’s dropped, but will be marked as inactive it if hits anything else.
  4. Changed the colour of the bomb to red

Manages Bombs

It happened that the code we had already written to manage bullets was already perfect for managing bombs as well.

We used Visual Studio Code’s built-in capability to automatically rename symbols to:

  1. Rename the bullets array to projectiles
  2. Rename the manageBullets() function to manageProjectiles()

This was enough to have bombs move, draw and be removed when it becomes inactive.

Dropping Bombs

We added a new function to Ememy called shoot(). In that function we generated a random number from one to two hundred. We then dropped a bomb every time that number was less than five (we tuned this small number to get a good rate of bomb drops). This meant that the enemy dropped a bomb at random intervals, to make it impossible for the player to anticipate.

Download

The files for this week can be found on our GitHub repository.

Creators: Shootah Part 5 – Edges

spaceship.png

This week we extended our colliders so that we could used them to prevent the player going off the edges of the screen. We used it to show how software design needs to evolve.

Colliders

Our colliders were designed to be connected to an object with three things:

  1. A property  containing the x-coordinate of its location
  2. A property y containing the y-coordinate of its location
  3. A function hit() which was called if the attached collider touched another collider

Something to Connect To

We had colliders already attached to our:

  1. Enemy
  2. Bullets

but we didn’t have anything to attach to that could represent the side of the screen.

We created a new class called Static() with nothing more than the x, y  and hit() that we needed so that we could connect a collider to it (stored in one more property – collider).

Screen Edges

We created a pair of these colliders positioned at the right and left-hand side of the screen. We made sure to add them to our list in check_colliders(). Nothing much happened. Why? Well, first, the Player didn’t have a collider, so we added one, liberally copying code from Enemy, which a minor change to the description argument.

Now we could see the contact occurring between the edge and the player, though nothing was stopping it moving yet.

Unintended Consequences

As  often happens with code, this change had unexpected consequences; bullets were not firing properly any more. Why? Because the player now had a collider and the bullets were becoming inactive immediately because they were hitting that. The fix was to modify the Bullet’s hit() function to ignore hitting a collider with the description “player”.

Stopping the Player Moving

We now knew our player was hitting an edge, but another problem became apparent: we didn’t know which edge!

To properly stop the player and stop it moving too far, we really needed to know which side of the player the collider we’d hit was, but that information wasn’t available to us with the current design.

A couple of quick changes were necessary:

  1. In Collider.touching(), instead of just passing the descriptors to the objects hit() functions, we changed it to pass the Collider itself.
  2. In all the hit() functions, we had to made a small adjustment to account for the fact that we were now getting a Collider and not just a string.

With the extra information from the collider, were were able to determine how far the player should be allowed to move to and prevent it going further by setting the x value appropriately.

Download

The files for this week can be found on our GitHub repository.

Creators: Shootah Part 4 – Colliders

 

This week we mainly dealt with building and using a box collider in our game. The box colliders are written in a way such that:

  • They are connected to something in the game and follow it around
    • What they are attached to must have the properties x and y for position
  • It is possible to test if they are touching each other
  • If two colliders are found to be touching, we tell the things that they’re attached to that they’ve been hit by something
    • What they are attached to must have a function hit() that we can call

 

Extents of the Collider

Our collider is a box, of a given width and height, centred on the x and y of the thing it’s connected to:

Untitled Diagram

For checking collisions, we need to know the values of the left and right side of the box and the y values of the top and the bottom of the box.

For convenience, we write a function which returns an object (using curly brackets) with the left, righttop, and bottom values (shortened lr, t and b respectively) as properties:

extents(){
  return {
    l: this.connected.x - this.width / 2,
    r: this.connected.x + this.width / 2,
    t: this.connected.y - this.height / 2,
    b: this.connected.y + this.height / 2
  };
}

When making an object like this, we set a property value by first writing the property name, followed by a  colon (:)  and then a space and the value we want it to have. Each property is separated with a comma. The don’t need to be on separate lines, but it makes it easier to read.

 

Touching Colliders

So how do we know that two colliders are touching? Actually there are four ways in which they definitely can’t be touching:

  • One is completely to the left of the other
  • One is completely to the right of the other
  • One is completely above the other
  • One is completely below the other

And if none of these are true, then it must be touching. So actually, we’re going to check that they’re not NOT touching (double negative, used correctly!).

How do we know if something is completely to the left of something else? Look at this diagram:

 

Untitled Diagram (1)

We know that box 2 (in blue) is totally to the left of box 1 (in orange) because we can see it is, but how could get the computer to check it? Remember, left and right are just x values on the screen. Box 2 is left of box 1 because both it’s left and right values are smaller than the left value of box 1.

The checks for the other directions are very similar:

  • The second box is right of the first box when both of it’s x values (left and right) are greater than the first’s right side.
  • The second box is above of the first box when both of it’s y values (top and bottom) are less than the first’s top side.
  • The second box is below of the first box when both of it’s y values (top and bottom) are greater than the first’s bottom side.

 

Sending Messages

Each collider has a property disc that describes the thing, or type of thing, that it’s connected to.

All colliders know what they’re connected to, so when we determine two have touched, we call a function called hit() on each of the connected objects, passing it the desc of the other collider. This means, in our game, when our enemy is hit, it can know that it’s been hit by a bullet – or maybe something else – and react appropriately.

 

Checking Every Collider Against Every Other

In our code, we gather all the active colliders at each frame. We then need to check each one against each every other one. How can we do that?

Consider a list of four items:

Untitled Diagram (2)

To check them all against each other we first need to check 0 against the other three. Simple enough.

We we need to check 1. But we don’t need to check 1 against 0, since we already did that. Nor do we need to check it against itself. We only need to check it against 2 and 3.

If we write out the full sequence, we see that for four items we need three passes to check all combinations:

  • First pass: Check 0-1, 0-2, 0-3
  • Second pass: Check 1-2, 1-3
  • Third pass: Check 2-3

We can write a pair of loops to do this:

for (let i = 0; i < c.length - 1; i++){
  for (let j = i + 1; j < c.length; j++){
    c[i].touching(c[j]);
  }
}

Note two things about these loops:

  • The first loop goes from zero, but stops one short of the last item in the list (i < c.length – 1). It picks the first item to be checked.
  • The second loop doesn’t start from zero. It starts from what ever i currently is, plus one. It picks the second item to be checked.

 

Other Stuff

We also did a few other things this week:

  1. We fixed a small bug that was keeping our spaceship moving when we didn’t want it.
  2. We added a little drag to slow the spaceship down to a stop when we lift our fingers off the keys
  3. We set bullets inactive when they hit something

 

Download

The files for this week can be found on our GitHub repository.

Creators – Shootah Part 3 – Enemies etc.

This week we continued our Shootah project. We did two main things;

  1. Changed the code to control the total number of bullets to those actually on screen
  2. Added an enemy that loops backwards and forwards across the screen

Controlling the Number of Bullets

In Part 2, we made a new bullet every time the user pressed the Up key and put it in the bullets list.

This meant that after a while we could have a lot of bullets, most off the top of the screen, which was even slowing some machines down.

To limit the number of bullets we did four things:

  1. Added a new property to the Bullet class called active and set it to be true
  2. In the move() function for the bullet class, we added a check for the bullet going off the top of the screen (this.y < 0) and, if true, set the active property to false
  3. In sketch.js, we moved the lines of code in the draw() function responsible for moving and drawing the bullets into a new function called manageBullets() and called it from draw().
  4. In manageBullets() we made a new list called active and put every bullet that was still active into it. We then made this the new bullets list.

We write a little code that printed out the total number of bullets to verify this was working.

Adding an Enemy

We added a new file called enemy.js and included it in the index.html file.

This file looked a lot like player.js. The main different was the move() function. Our enemy moves constantly left-to-right. When it gets too far off the right-hand side of the screen (checked in move()) we set its x position to be off the left-hand side of the screen instead. This makes it loop around.

TODO

We still have loads to do and we made a list on the day:

  • No more infinite bullets!
  • Check edges so spaceship doesn’t disappear
  • Enemies
  • Collision detection
  • Enemies shoot back (bombs)
  • Lives/score
  • Levels
  • Background music
  • Moving background
  • Story

We’ve done two and we’ll do some of the others for sure.

Download

The files for this week can be found on our GitHub repository.

 

Bodgers – FreeCAD and Fritzing

Hello again everyone

This week we continued working on our Astro Pi entries and we also looked at FreeCAD and Fritzing which are tools that will help us with building our projects.

fritzing_freecad

FreeCAD, available for download from here, is used for 3D modelling and allows us design very complicated things from simple 3D shapes such as cubes and cylinders. Here are a couple of quick videos to get you started.

Then we looked at Fritzing, download from here, an application for drawing very easy to understand circuits, here’s how to draw a simple circuit using it.

 

Dave will be leading next Saturday’s session and I will see you again on the ninth of Feb.

Declan, Dave and Alaidh.

Bodgers – Mission Zero & Projects

Hello again everyone.

This week we started getting our entries ready for the Astro Pi Mission Zero Challenge by looking at whose aboard the International Space Station now and what they’re doing. We followed this up by taking another look at programming the Trinket Astro Pi emulator.

31348827717_cd45388c8b_z

We also had a small brainstorming session to come up with ideas for projects that we will be working on for the rest of the year.

img_20190119_135038472_hdr

See you all next Saturday.

Declan, Dave and Alaidh.

Bodgers – Motors and Robots

This week in the Bodgers group we looked at controlling motors and robots withe the Raspberry Pi.

You can find the code for this weeks session here and my notes are here motors and robots

We also talked about ideas for the projects we will be working on for the rest of the year. Tomorrow we will continue to look at robots and we will also do some brain-storming for our projects.

See you then.

Declan, Dave and Alaidh

Creators – Pixels

543px-Liquid_Crystal_Display_Macro_Example_zoom

This week we looked at pixels. Your screen is made up of thousands of them; the picture on it is created by setting each one to the correct colour. We may ask P5 for an ellipse(), but ultimately some piece of code is deciding which pixels to change to the currently selected fill() colour (for the centre) and which to set to the currently selected stroke() colour (for the edges).

Working with Pixels in P5

P5 contains two main functions for working with pixels. The first is loadPixels(). By default it reads all the pixels from the canvas and copies the information into a huge array (or list) called pixels[].

If we then make a change to pixels[], all we have to do is call updatePixels() to copy this information back to the canvas again.

Sound easy? It almost is, but the content of pixels[] isn’t immediately obvious.

Structure of the pixels[] Array

The pixel[] array is one long list of numbers. It is arranged such all the information for the first row on the canvas is first, followed by the information for the second and so on until the bottom of the canvas.

For each pixel there are four numbers representing the red (R), green (G), blue (B) and alpha/transparency (A) value of the pixel. By the time the pixel has reached the  screen, alpha has no more meaning, so we will ignore it and concentrate on the RGB values.

This diagram represents what we’ve been talking about:

pixel diagram

Getting and Setting a Pixel

To make it easy to get and change the value of a specific pixel we can write two functions:

  • getPixel(x, y) which returns an array containing [r, g, b] values
  • setPixel(x, y, colour) where colour is an array containing [r, g, b] values

Both these functions rely on knowing where in pixels[] the data for the pixel at (x, y) is.

We can work out this as:

  1. Location of R: 4 * ((y * width) + x)
  2. Location of G; Location of R + 1
  3. Location of B: Location of R + 2

Knowing this, the functions can be written as:

function getPixel(x, y){
  let loc = 4 * ((y * width) + x);

  return [pixels[loc + 0],
          pixels[loc + 1],
          pixels[loc + 2]];
}

function setPixel(x, y, c){
  let loc = 4 * ((y * width) + x);
  
  pixels[loc + 0] = c[0];
  pixels[loc + 1] = c[1];
  pixels[loc + 2] = c[2];
}

FIlters
We wrote three filters, all very similar. Each used loops to go over each pixel in turn, retrieve the current colour, change it in some way and set it back.
The first was fade(amount) which took a number between 0 -> 1 for amount. It multiplied each of the original RGB values from the pixel with this value. The closer to zero amount was, the more it faded the image to black.
The second was invert(). It subtracted each RGB value from 255. This has the effect of inverting all colours in the image.
The final one was vignette(). This is like fade() but fades pixels depending on how close to the edge of the picture they are.
Animating Fade
Finally, we also animated fade() so that the picture started black and got brighter over a number of frames.
Putting all the filters together:

Download

The files for this week can be found on our GitHub repository.

 

 

Explorers – Doubling

Introduction

For our first day back in 2019 we decided to do a simple Paper folding program.

It doesn’t really fold paper though, it just shows you how thick the paper gets when you keep folding it in half! It will get very thick quite quickly!

So we Googled, how thick is a sheet of Paper and we got the number 0.1mm, so quite thin really!

We then Googled a list of items and their heights, so we could write out a message when we reached that height, this was the list we came up with [and a guess of how many folds it would take]:

  • Paper: 0.1mm
  • Baby: 530mm
  • Human: 2 Meters [50]
  • Dublin Spire: 121m
  • Croagh Patrick: 764m
  • Burj Khaleefa: 828m [10,000]
  • Carauntoohill: 1038m [1 billion]
  • Mount Everest: 8848m
  • Galway to America: 6603km [25]
  • Space: 100km
  • Moon:300,000km
  • Mars: 56,000,000 km
  • Sun: 150,000,000 km
  • Pluto: 7,500,000,000 KM

The Program

In order to keep track of how many folds we have done and what height the paper has reached we needed a few variables:

We store the number of folds, and the height in mm, meters and kilometers.

  • folds – to store how many times we have folded the paper
  • mm – to store the height in milimetres
  • metre – to store the height in metres
  • km – to store the height in kilometres

variables

We then made sure that they were all set to the correct value when the Green Flag was clicked.

greenflag

The only one that is not zero is the height in mm which we set the thickness of paper 0.1

Now we can get coding.

We used the Up and Down arrows to fold/unfold the Paper, this would increase/decrease the number of folds and the mm height and then Broadcast to the code that checked everything else.

upanddownarrows

The code that does the checking needs a few IF’s to work out what to do. First of all though it needs to calculate the height in Metres and Kilometres as well.

We used the number of folds to work out if we should be checking the mm, metre or km variable. All we did when we got to a particular height was to Say something on the Screen, but you could do anything you want at these points in the code, maybe show a different sprite or make a sound or something.

This is the code that checked the mm and metre variables

mmandmetre

 

and this is the code that checked the metre and km variables

metreandkm

And if anyone wants the full project, it is availabe on the scratch.mit.edu web site:

User: cdexplorers1819
Password: exploreres1819
Project: Doubling

Demos and Pizza – Christmas 2018

Here are photos from our Christmas party and Show & Tell day at CoderDojo Athenry on 08 December 2018.

This slideshow requires JavaScript.

It was fantastic to see the things that our young people had created.

We are very grateful to our supporters in the community around Athenry:

  • Clarin College and Principal Ciaran Folan, who are so generous with their space every week
  • Galway & Roscommon Education & Training Board, who provide us with an annual Youth Club Grant
  • HEA (Higher Education Authority) and NUI Galway School of Computer Science, who provide us with funding towards equipment.
  • Medtronic and Declan Fox, who have provided us with a grant linked to Declan’s volunteering
  • Hewlett Packard Enterprise and Mark Davis, who provide us with loaner laptops
  • Boston Scientific and Kevin Madden, who provide us with the loan of 3D printers.
  • Supermacs, who gave us a great deal on the food for the Christmas party

And of course, we are eternally grateful to our wonderful mentors, and to the parents who come along with their children every week. Thank you!