Category Archives: Game Development

Getting Started with iOS for a C# Programmer – Part 6 – Graphics

In this post I set out to create a series of posts that would walk through creating a basic game in Swift. In the post preceding this one I covered collision, and now we are moving on to graphics.

Add Assets

The secret to graphics in Swift seems to be creating assets. If you look to the left hand side of your project, you should see an asset store:

This can be added to:

Create a new image here (in fact, we’ll need two):

Then drag and drop your icons. Mine were kindly provided by my daughter:

Use SKSpriteNode

Once you have an image, it’s a straight-forward process to map it to the game sprite (for which we are currently using a rectangle). As you can see in GameScene.swift, very little actually changes:

    func createAlien(point: CGPoint) -> SKSpriteNode {
        let size = CGSize(width: 40, height: 30)
        //let alien = SKShapeNode(rectOf: size)
        let alien = SKSpriteNode(imageNamed: "alienImage")
        alien.size = size
        //print(self.frame.minY, self.frame.maxY, self.frame.minX, self.frame.maxX, self.frame.width, self.frame.height)
        alien.position = point
        //alien.strokeColor = SKColor(red: 0.0/255.0, green: 200.0/255.0, blue: 0.0/255.0, alpha: 1.0)
        //alien.lineWidth = 4
        alien.physicsBody = SKPhysicsBody(rectangleOf: size)
        alien.physicsBody?.affectedByGravity = false
        alien.physicsBody?.isDynamic = true
        alien.physicsBody?.categoryBitMask = collisionAlien
        alien.physicsBody?.collisionBitMask = 0
        alien.physicsBody?.contactTestBitMask = collisionPlayer
        = "alien"
        return alien


It’s worth bearing in mind that this will simply replace the existing rectangles with graphics. As you can probably see from the images above, mine are neither straight, trimmed, nor centered, and so it looks a little skewed in the game. Nevertheless, we’re now in the territory of a playable game:

We’re not there yet, though. The next post is the final one, in which we’ll add a score, deal with the overlapping aliens and probably reduce the size of the ship. Also, if you run this, you’ll see that after a short amount of time, it uses a huge amount of memory tracking all the aliens, so we’ll limit the number of aliens.


Getting Started With iOS for a C# Programmer – Part Four – Controlling an Object

In this post, we covered how to move an object on the screen; this time, we’re going to control it. However, before we do, let’s change the game orientation to landscape only, as that’s really the only thing that makes sense on an iPhone for this type of game.


The first thing to do is to change the code in the GameViewController to force the orienetation to landscape:

    override var shouldAutorotate: Bool {
        return true

    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        if UIDevice.current.userInterfaceIdiom == .phone || UIDevice.current.userInterfaceIdiom == .pad {
            return .landscape
        } else {
            return .all

When you run the simulator, the game will now appear on its side; to rectify that, select Hardware -> Rotate Left*:


As you may have noticed from the previous post, we do have a modicum of control over the rectangle; let’s now change that so that we can press to the left and have it move left, or on the right and have it move right.

Left and Right

It turns out that this is pretty easy once you understand how the co-ordinates work in Swift:

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for t in touches {
            self.touchDown(atPoint: t.location(in: player!))

And the touchDown function:

func touchDown(atPoint pos : CGPoint) {
        print (pos.x, pos.y)
        var halfWidth = (player?.frame.width)! / 2;
        if (pos.x < -halfWidth) {
            playerSpeed? -= CGFloat(1.0);
        } else if (pos.x > halfWidth) {
            playerSpeed? += CGFloat(1.0);

Finally, we need the update event to do something with the playerSpeed:

    override func update(_ currentTime: TimeInterval) {
        // Called before each frame is rendered
        player?.position.x += playerSpeed!

Now we have a game where we can move the player left and right.

Tidy up

To clean up the screen before we get into firing, it would be nice if the player was lower down the screen, and a slightly different colour:

func CreatePlayer() -> SKShapeNode {
        let playerSize = CGSize(width: 100, height: 10)
        let player = SKShapeNode(rectOf: playerSize)
        print(self.frame.minY, self.frame.maxY, self.frame.minX, self.frame.maxX, self.frame.width, self.frame.height)
        player.position = CGPoint(x:self.frame.midX, y:-150)
        player.strokeColor = SKColor(red: 0.0/255.0, green: 0.0/255.0, blue: 200.0/255.0, alpha: 1.0)
        player.lineWidth = 1
        player.physicsBody = SKPhysicsBody(rectangleOf: playerSize)
        player.physicsBody?.affectedByGravity = false
        player.physicsBody?.isDynamic = true
        return player

Remember, this is a landscape only game.


Okay – so firing is just an extra clause in our touchDown function:

    func touchDown(atPoint pos : CGPoint) {
        print (pos.x, pos.y)
        var halfWidth = (player?.frame.width)! / 2;
        if (pos.x < -halfWidth) {
            playerSpeed? -= CGFloat(1.0);
        } else if (pos.x > halfWidth) {
            playerSpeed? += CGFloat(1.0);
        } else {

    func Fire() {
        let bullet = CreateBullet(point: (player?.position)!)

    func CreateBullet(point : CGPoint) -> SKShapeNode {
        let bulletSize = CGSize(width: 1, height: 10)
        let bullet = SKShapeNode(rectOf: bulletSize)
        //print(self.frame.minY, self.frame.maxY, self.frame.minX, self.frame.maxX, self.frame.width, self.frame.height)
        bullet.position = point
        bullet.strokeColor = SKColor(red: 0.0/255.0, green: 0.0/255.0, blue: 200.0/255.0, alpha: 1.0)
        bullet.lineWidth = 4
        bullet.physicsBody = SKPhysicsBody(rectangleOf: bulletSize)
        bullet.physicsBody?.affectedByGravity = false
        bullet.physicsBody?.isDynamic = true
        = "bullet"
        return bullet

All we’ve actually done here is to create a new rectangle, and sourced it right at the centre of the player. We’ve added it to the self construct, so the automatic rendering will pick it up; next, we need to move it:

    override func update(_ currentTime: TimeInterval) {
        // Called before each frame is rendered
        player?.position.x += playerSpeed!
        self.enumerateChildNodes(withName: "bullet") {
            (node, _) in
            node.position.y += 1


* Remember, when holding an iPhone or iPad, the button should always be on the right hand side – without wishing to judge, anyone that feels different is wrong, and very possibly evil.


Rotate a Shape Around an Axis Using HTML5 and Javascript

Imagine, for a minute, that you want to rotate a red square around its centre… on a web page. Following on from my previous post about games using HTML5 / JS this post details how to do such a thing.


Before drawing a rectangle, rotating it, or anything else, you need a context:

var canvas = document.getElementById("mainCanvas");
var ctx = canvas.getContext("2d");

Now you have a context, you can do things like clear the canvas; for example:

ctx.clearRect(0, 0, windowWidth, windowHeight);


In HTML5, you have three methods that will be of use, and the first, and probably most important, is fillRect. It is impossible to rotate a square around its centre without a square. The syntax for fillRect is probably as you would expect:

ctx.fillRect(x, y, width, height);


The syntax for rotation is this:

ctx.rotate(rotationDegree * Math.PI / 180);

Whilst I may, during my school years, have been able to explain the sum above – I just copied it from the internet. Given the number of places where is looks exactly alike, I would guess that I’m not the first person to do that.

Just using the three lines above will give you a rotating rectangle; however, the rotation axis will be 0, 0. It took me a while to understand exactly how this works, but the key is `translate`.


To me, this function is completely counter-intuitive. What it does it to offset the centre of the context by the parameters given. If the initial centre is 0, 0 (which it is by default), the following line will make it 10, 10:

ctx.translate(10, 10);

The centre of the context is 10, 10; if I call it a second time:

ctx.translate(10, 10);

The centre of the context is now 20, 20! There are two ways to reset the offset – you can simply negate the offset (by calling it with negative values), or you can call before the change, and ctx.restore() afterwards.

Putting it all together

So, what does all this look like in a single coherent piece of code:

        var canvas = document.getElementById("mainCanvas");
        var ctx = canvas.getContext("2d");
        ctx.clearRect(0, 0, windowWidth, windowHeight);

        var halfWidth = (iconWidth / 2);
        var halfHeight = (iconHeight / 2);

        var centreX = x - halfWidth;
        var centreY = y - halfHeight;

        ctx.fillStyle = "#FF0000";
        ctx.translate(centreX, centreY);
        ctx.rotate(rotationDegree * Math.PI / 180);
        ctx.fillRect(-halfWidth, -halfHeight, iconWidth, iconHeight);

        ctx.translate(-centreX, -centreY);

The key part to note here is the call to fillRect. Because the translate has now set the centre to be the centre of the drawn image, the image needs to be positioned at -(image width / 2).

… and you, too can have a spinning red rectangle on your screen.


Basic Game Using HTML5 and Javascript

This article discusses how to go about creating a basic game loop in HTML5 / JS and to implement control over a sprite.


A few years ago, when Microsoft released the idea of WinJS, I wrote a game in HTML5/JS (or WinJS – they are not exactly the same).

I recently decided to see if I could write a web game, using just HTML5 and Javascript. This article covers the initial POC and results in a small red square navigating around the screen:

Game Loop

Looking at established game frameworks, they all basically give you the same things:
– A game loop, consisting of an update and draw phase
– Some helper methods for manipulating graphics, or rendering them to the screen

My attempt will be different, I’ll just provide a game loop; here it is:

(function MainGame() {    

    setInterval(function() {
    }, 20);

The loop executes every 20ms, meaning that there are 50 frames per second.


Basically, what the HTML gives us here is a canvas; so the page is very simple:

    <script type="text/javascript" src="./gamelogic.js" ></script>
<body onresize="onResizeGameWindow()">    
    <canvas id="mainCanvas" style="width: 100%; height: 100%"
        onkeydown="onKeyDown()" tabindex="0">

There are two events handled here, because there are two things that the player can do: they can interact with the game (i.e. press a key), and they can resize the browser window. We need to react to both.


Let’s have a look at the draw function next. All this is, is a way of displaying all the objects on the screen in a controlled fashion:

    function Draw() {
        var canvas = document.getElementById("mainCanvas");
        var ctx = canvas.getContext("2d");
        ctx.clearRect(0, 0, windowWidth, windowHeight);

        ctx.fillStyle = "#FF0000";
        ctx.fillRect(x, y, iconWidth, iconHeight);

As you can see, there are effectively two parts to this function: firstly, the canvas is cleared, and then the items (in this case, a single item) are drawn to the screen. The important variables here are x and y, because that dictates where the square is drawn; the rest could be hard-coded values.


    function Update() {        
        if (initialised == 0) {

        // Bounce
        if (x >= (windowWidth - iconWidth) 
            && directionX > 0)
            directionX = -1;
        else if (x <= 0 && directionX < 0)
            directionX = 1;

        if (y >= (windowHeight - iconHeight)
            && directionY > 0)
            directionY = -1;
        else if (y <= 0 && directionY < 0)
            directionY = 1;

        // Move
        x += directionX * speed;
        y += directionY * speed;

There are three parts to the Update. The first is to perform any initialisation: in my case, I focus on the canvas and call the resize event here. This potentially could be done on an event, but you would still have to check inside this loop if it had been done. The second is to stop the player leaving the screen; and finally, we adjust the player position.


As you saw earlier, there are two events that are handled; the first is the user resizing the screen:

function onResizeGameWindow() {
    var canvas = document.getElementById("mainCanvas");
    windowWidth = canvas.width;
    windowHeight = canvas.height;

This basically ensures that the game adjusts to the browser dimensions. This might also be where you would determine if the window was made so small that the game could no longer be played.

The second event was the keydown event. This effectively provides the control for the player:

function onKeyDown(e) {
    if (!e) e = window.event;     

    if (e.keyCode == 39) {
    else if (e.keyCode == 37) {

    if (e.keyCode == 38) {        
    else if (e.keyCode == 40) {        

The top line is because the parameter comes through as null.


If you run this game, you’ll see that you can move the square around the screen, increase and decrease its speed, and stop. Not exactly the next Call Of Duty, I’ll grant you, but the foundation of a game, certainly.

Building Block Game in Unity 3D

Not sure this qualifies as a game, but it’s a computerised version of the building blocks that you might give to a three-year-old. What can I say, it was a nice way to spend a Sunday afternoon !

Here’s what the finished game / program looks like:

The Script

There is only one script:

public class BehaviourScript : MonoBehaviour
    private Vector3 screenPoint;
    private Vector3 offset;
    void OnMouseDown()
        screenPoint = Camera.main.WorldToScreenPoint(gameObject.transform.position);
        offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
    void OnMouseDrag()
        Vector3 cursorPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
        Vector3 cursorPosition = Camera.main.ScreenToWorldPoint(cursorPoint) + offset;
        if (cursorPosition.y > 0)
            transform.position = cursorPosition;

The Scene

Basically, the blocks are standard unit cubes with a wood texture, a rigid body and the above script attached:

Mesh Colliders in Unity

Mesh colliders are, generally speaking, a bad idea in Unity. The reason being that they cause collision based on the detailed mesh that forms the object. This is bad, basically because this generates many collision points. Consider this object:


As you can see, it’s a basic cylinder (a cup), so a box collider would add eight collision points. A mesh collider generates a point for each of the 496 vertices.


So, whilst it’s more accurate, it uses more resources.

Okay, so now I’ve said why you shouldn’t use a mesh collider, I’ll cover how to use them.

Firstly, you need to add a mesh collider:


There are three important things to note here:

  1. There is a mesh collider
  2. It is convex
    1. The convex flag allows the collider to collide with other colliders
  3. It is not a trigger
    1. The trigger flag turns the collision into a programmatic notification only

The manual for this is here.

Adding Cheats and Features to a Unity Game for Development Only

I’m currently writing a breakout style game (which, if you’ve seen any of my previous posts, you might have divined). One of the things that I would like to do with this, without having to play through all the levels is to complete the level quickly. This led me down the path of creating a “Cheat” button. However, for those amongst you that remember the ZX Spectrum, the makers of Jet Set Willy may have had a similar idea, but left the “Pokes” in the final game.

To avoid this, I thought it must be possible to use a feature such as the compiler directive in C#. In fact it is. Unity has its own, and one is to determine whether you’re running in the editor.

Here’s how I conditionally display the button:

    void OnGUI()
        if (GUI.Button(new Rect(10, 30, 50, 30), "Cheat"))
            var o = GameObject.FindGameObjectsWithTag("Brick");
            foreach (var b in o)
                var r = b.GetComponent<Rigidbody>();
	        r.transform.position += new Vector3(0, 0, zOffset);
                r.useGravity = true;

This particular cheat just makes all of the bricks fall out of the sky. UNITY_EDITOR is one of a list of pre-defined “Platform Defines” that can be found here.

Saving and Loading Level Data in Unity

This describes a method of persisting data in Unity. For example, saving and loading the current game level.

The first thing that you will need is to create a helper class to read and write the data that you need:

        public static void SaveGameState()
            XmlDocument xml = new XmlDocument();
            var el = xml.CreateElement("PlayerStatus");
            el.SetAttribute("CurrentLevel", Application.loadedLevel.ToString());

        public static void LoadGameState()
            XmlDocument xml = new XmlDocument();
            var el = xml.GetElementsByTagName("PlayerStatus")[0];
            string currentLevel = el.Attributes["CurrentLevel"].Value;
            int loadLevel = 0;
            if (!string.IsNullOrEmpty(currentLevel))
                loadLevel = int.Parse(currentLevel);
                if (Application.loadedLevel != loadLevel)

The next stage is to plug this into Unity. I put the following in a Master Script (which is essentially just a script associated with an empty game object).

    void OnApplicationQuit()

    void Start()

I’ve seen plenty of articles on using serialisation for this, and that would obviously have the same effect, but this is another option.

Working with the threading system in Unity

Unity seems to have a multi-threaded system, but I could find no way of accessing the dispatcher. Consequently, it’s necessary to create some kind of self-rolled task queue. The specific problem that I faced was with using the timer; here’s the code for the timer:

public class MasterScript : MonoBehaviour
    private Timer _timer;

    void Start ()
        _timer = new Timer();
        _timer.Interval = 1000;
        _timer.Elapsed += _timer_Elapsed;

    private void _timer_Elapsed(object sender, ElapsedEventArgs e)

The idea being that every second, and new object would appear on the screen. However, as soon as you run this, it crashes (or as close as Unity comes to crashing):

FindGameObjectWithTag can only be called from the main thread

The solution that I came up with was as follows:

public class MasterScript : MonoBehaviour
    public static Queue<Action> TaskQueue;

    private void _timer_Elapsed(object sender, ElapsedEventArgs e)

    private void SpawnNewObject()
        TaskQueue.Enqueue(() =>
            var newObj = Instantiate<GameObject>(MyObject);

Then, simply change the Update function to run them:

    void Update ()
        if (TaskQueue.Count > 0)

I’ve used the idea of a “Master Script” to deal with the queue, and this can be queued to from somewhere else in the game, which makes it more flexible.

Advancing to the next Level in Unity

I’m quite new to Unity, and so thought I would start blogging useful things that I’ve discovered. Obviously, there is the which is basically where all this information comes from, and also an excellent tutorial on YouTube. I found this after trying a Pluralsight course on Unity, but rapidly losing the will to live while watching it.

In my particular example, I have a game, whereby touching a specific object progresses to the next level. Here’s the code (against the target object):

    void OnCollisionEnter()
        if (Application.loadedLevel < Application.levelCount)
            Application.LoadLevel(Application.loadedLevel + 1);

I admit, it’s not exactly rocket science, but it took me a while to work this out. I spent some time trying to parse the level name, and other workarounds, before I spotted that it’s all in the Application object.