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Forgotten Parallax Bicycles

The forgotten parallax bicycles. In June last year (that feels weird to type), I created another one of my little HTML5 Canvas demos - this time of some hills that parallaxly scroll with a bicycle on a road. I actually made it as a (birthday?) present for someone I seem to remember - and I even released it on my website here, but I somehow seem to have forgotten to post about it here on my blog, so I'm doing so now :-)

You can find it here: Parallax Bicycle

At the time the bicycle itself in particular was incredibly fiddly to get working right if I recall correctly. The hills in the background are procedurally generated too - they are on a (seamless!) loop and repeat every so often. The seamless part was also interesting to get working right.

Transform your javascript with Browserify

Tired of battling endless <script> tags in your html files? Fed up with messing with a dozen libraries cluttering up the place? Can't see the wood from the trees? Try browserify (+ rollupify + wzrd)! It's amazing! It's awesome! It tidies up your code for you, so you don't have to (perhaps not :P)!

Seriously though, I've just been playing around with browserify, and it's awesome. It's that missing thing I've been trying to find for a long time. But what does it actually do, you ask?

Well, perhaps it's best to use an example. Consider these (relatively) harmless javascript files:

// SillySay.js
"use strict";

function sillySay(sentence) {
    // Split the sentence up into words
    var words = splitWords(sentence);

    // Loop over all the words in the above array and display them one by one
    for(let i in words) {
// WordSplitter.js
"use strict";
function splitWords(sentence) {
    // Split the sentence on whitespace and return the resulting array
    return sentence.split(/\s+/g);

To use our (perfectly ridiculous) example code, we not only have to include SillySay.js, but WordSplitter.js (this could be a library you use for example) as well:

<!DOCTYPE html>
        <meta charset='utf-8' />
        <title>Silly Say Demo</title>
        <p>Silly Say Demo</p>
        <p>By <a href="">Starbeamrainbowlabs</a></p>

        <script src="WordSplitter.js"></script>
        <script src="SillySay.js" charset="utf-8"></script>
            window.addEventListener("load", function(event) {
                sillySay("This is a test");

            html, body { font-size: 100%; }
                font-family: sans-serif;

That's looking a bit messy, but imagine what it'd be like if you added another few libraries? Or a new feature in a separate file? See the problem? Browserify solves just this issue. It analyses the dependencies of the entry point to your app, and bundles up all your code into a single file, nice and neat. You can add extra transforms (like plugins), too, to do extra things like automatically insert your app's version, or include other data files automatically, or transpile other languages to javascript automagically (full list here).

Sounds cool yet? Let me give you a quick tutorial on how I set up Browserify, with Rollupify and Wzrd.

Firstly, we need to set things up. If you don't have Node.js installed, do that now. You'll also get npm - Node's (perfectly awesome!) package manager. Next, let's create a quick project and paste in the code above. I've recorded an asciicast (as you may have seen a few times before here) of me going through the process:

(Can't see the asciicast above? Try viewing it here.)

If you'd like to take a look at the final result, as written in the asciicast above, you can find it over here. Questions and comments are welcome below :-)

ES6 Features 13: Classes

Almost a year ago I finished a series on the new features of Ecmascript 6, the next version of Javascript. At the time there were one or two features remaining that I hadn't covered, but I didn't feel that today's browsers supported them well enough for me to write a blog post on them. Today, however, that has changed, for classes at least. In this blog post I'll explain by example how classes work in ES6.

Originally, I was against the idea of having classes in javascript. After using them for a while, I've decided to change my mind. They can bring organisation to an otherwise rather cluttered project, especially since the modules syntax hasn't yet landed.

If you've you're familiar C♯, then ES6 classes will feel a little bit familiar. Here's a simple example:

"use strict";
class Bicycle
    constructor(inPosition, inColour)
        this.pos = inPosition;
        this.colour = inColour;
        this.wheelCount = 2;




        // Do rendering stuff

Very familiar (I hope). Classes in ES6 are defined using the class Tree { } syntax, with everything belonging to that class inside a set of curly braces, just like in C♯. Because javascript isn't a typesafe language, method declarations look a bit different. Essentially they are the same as a C♯ method declaration, just with the type names taken out.

The "use strict"; at the top is important - today's browsers don't let you use classes without it. I'll omit it in later examples for sake of simplicity, but you'll always need to remember to include it when using ES6 classes.

The constructor() method is, as you've probably guessed, the constructor of your class. Strange way of doing things, I know, but that's how it's declared. Note also that all variable initialisation is done in the constructor and not in the class body. Apparently class definitions are supposed to define an object's capabilities and not its members.

Calling a method from inside is an ES6 is easy too (see highlighted line #8), but it's important to understand what the this variable is in this context first (I could write a whole separate blog post about this). this is a special variable in javascript that holds the current context. In the case of an ES6 class, it holds the current instance of the current class. This is identical to C♯, but the difference is that you'd normally never need to use this in C♯ and it's required in ES6 - for both method access and variable access.

class Tree
    grow(dt, rate)
        this.classMethodA(4, dt, this.someVariable);

    // ...

White noise

Update: It turns out that ES6 does indeed support static methods (but not variables I don't think) natively via the static keyword. Here's an example:

class Tree
        this.something = Tree.doComplicatedStuff();
        this.somethingElse = this.constructor.doComplicatedStuff();

    static doComplicatedStuff()
        // ...!

Native static methods can be called in two ways (highlighted above). One is practically the same as the C♯ way of doing things, and the other is useful if for whatever reason you don't have the name of your own class handy.

Original sectional text

You can define static variables and methods too, although it's a little bit of a hack. Imagine I have this class:

class NoiseGenerator
        // ...!

        // ...!
Let's pretend that we want all our noise generated with our class to use the same seedable random number generator. How about rand = new MyPRNG();? Or window.rand = new MyPRNG();? Or even this.rand = new MyPRNG()? Unfortunately, all of these methods have at least one problem with them (if you know what's wrong with them, comment down below!). Don't despair though, because we can exploit the fact that classes themselves are objects - and aren't read-only. With this knowledge, we can do something like this:

NoiseGenerator.rand = new MyPRNG(someSeed);
Remember to put the above _after_ the class definition - ES6 classes are a little bit like C++ classes in that they don't exist until the interpreter has executed them (unlike regular old functions). Then in the body of a method, you can access it with something like `NoiseGenerator.rand.nextInt(0, 10);`.

Too many classes

ES6 classes do infact support inheritance under the guise of sub classing. A good example is worth a thousand words I think:

class Vehicle
        // ...

        console.log("Moving vehicle...");

    start() { console.log("Starting..."); }
    stop() { console.log("Stopping."); }

class Train extends Vehicle
        console.log("Moving train...");

As demonstrated in the example above, classes can inherit from one another with the extends keyword instead of C♯'s colon. The super word replaces the functionality of C♯'s base keyword too. Other than that, there really isn't a lot more to say about inheritance in ES6 besides the fact that almost everything not described works as you'd expect it to in C♯.

That concludes my whirlwind tour of classes in ES6. If I explained in detail every little feature, you'd be here all week reading about it (and I'd be here for the better part of a month writing this post!). ES6 classes also support getters and setters, overriding the default constructor, and more.

Sources and further reading

SnoozeSquad.js - Finally a decent lazy image loader

It's been on my todo list for positively ages, but I've finally gotten around to replacing the existing lazy image loading on this website (not on the blog yet, sorry!) with a new one of my own devising.

Lazy image loading is a technique in which you only load images no a given webpage if they are near the user's field of view. This saves bandwidth by preventing images that are never seen from being downloaded.

Since I've been unable to find a good, solid, reliable lazy image loading script on the web, I thought it best to post about it here so that you can use it too.

Link: SnoozeSquad (Direct download)

Procedural Castle Generation

See the Pen Procedural Castle Generator by Starbeamrainbowlabs (@sbrl) on CodePen.

(Full screen)

The subreddit /r/proceduralgeneration has recently set up monthly challenges, and after missing the first one I decided to enter the second one. February's challenge was to generate random castles procedurally. The challenge was a lot of fun to take part in - my entry can be seen above.

I've published the code behind my entry on Github, too if you're interested in checking it out.

There were 15 other entries apart from mine. Here are all the entries next to each other:

All the entries

(Full size image [15MB])

I liked zapetch's because although it's 2D, the generated castles are very varied and they look nice and simple. Moosekk's was great too - The towers look complicated and it has buildings and trees too. Comment down below with your favourites. Why did you like them? Voting is now open - please go and vote here. Your votes will decide who gets to decide on the next challenge!

How it works

Since I can't write a post on something that I've done without explaining just a little bit about how it works, I've written up a quick overview below. If anyone is interested in a longer writeup or any specific part of the generator, please comment down below and I will get back to you as soon as I can.

The generator works by picking a random regular shape, and then randomly altering the location of each of the resulting corners a little bit. After that the towers (and their stairs) and the keep are generated, and the flags are placed. Since the wind only flows in one direction, all the flags all face the same direction.

The moat is generated as a closed smooth line, with it's control points generated by taking the corners of the castle and moving them a set distance away from the main keep. Since the moat originally was way too wide for the drawbridge (whose parameters don't actually have anything to do with the moat at all!), I added a pair of extra control points to the moat's smooth line to bring it closer to the 2 towers that sit either side of the entrance (the moat was built intentionally, right?).

Originally I was going to generate random buildings inside the castle and draw paths between them, the towers, the keep, and the entrance, but the maths behind that got rather complicated and I didn't have time to wrap my head around it. I was also going to generate random people in the castle too, but again I didn't have time for this. I'll probably come back to this at a later date and work on these features.

If this challenge looks interesting, then /r/proceduralgeneration are hosting another challenge this month - this time the challenge is to procedurally generate a side-scrolling platformer.

Drawing (rotating) shapes

Rotating shapes.

After writing the smooth line class last week I wanted to write another one, and I decided to write a class to aid the drawing regular shapes. While writing the library I found myself with some rather nice looking rotating shapes that I thought would make a good blog post here.

Before I go any further, here's the demo:

See the Pen Rotating shapes by Starbeamrainbowlabs (@sbrl) on CodePen.

The background is a just a set of fancy css3 radial and linear gradients layered on top of one another. The interesting part is the calculating of the points in each shape - let me explain with a hexagon.

Shape drawing explained.

In the above, the hexagon I am drawing is shown in red, and a circle in green. In order to work out the co-ordinates for each corner (or vertex) of the hexagon, we can walk around a circle and note down our location at regular intervals (shown by the blue lines). I learnt this trick from this stack overflow answer. They can explain it much better than I probably could:

Let's assume you want to draw an N-sided polygon of radius r, centred at (0,0). Then the n vertices are given by:

x[n] = r * cos(2*pi*n/N)
y[n] = r * sin(2*pi*n/N)

where 0 <= n < N. Note that cos and sin here are working in radians, not degrees (this is pretty common in most programming languages).

If you want a different centre, then just add the coordinates of the centre point to each (x[n], y[n]). If you want a different orientation, you just need to add a constant angle. So the general form is:

x[n] = r * cos(2*pi*n/N + theta) + x_centre
y[n] = r * sin(2*pi*n/N + theta) + y_centre

By Answerer Avatar Oliver Charlesworth. Source: Stack Overflow

Anyway, here's the code I came up with:

I can't think of anything else I wanted to say, so I think I'll end this post here. Please comment down below if you have anything you want to say :)

Easy Smooth Lines with Bezier Curves

The smooth line class in action.

A while ago I wrote a vector class and a bezier curve class for my 2D graphics University ACW (Assessed CourseWork). After packaging them up and posting them here, I thought it a good idea to take a step further and write a smooth line class too, to start building up a library of implementations of various different algorithms.

While I was searching for a good alternative to jsbin (it doesn't let me use tabs instead of spaces), I came across Codepen again, and finally decided to take a look. Apparently you can do quite a bit with a free account, so I signed up and posted about new my account on this blog.

Since the quality of the content on Codepen is considerably high, and you can see who has done what, I've decided to put more time into the visual effects of the things that I put up on there.

Anyway, here's a demo of my SmoothLine class in action:

See the Pen Smooth Lines by Starbeamrainbowlabs (@sbrl) on CodePen.

Click to add a point. A line will show up when you have 3 points. Here's the class itself:

Note that it depends on my earlier Vector and BezierCurve classes (links above).

The code is actually really simple. You create a new instance of the SmoothLine class, add some Vector points with the add() method (it takes both a single vector and an array of vectors), and then call the line() method when you are reading to add the SmoothLine to your drawing context path.

Here's some example code:

// Creation code
var smoothLine = new SmoothLine();
smoothline.add(new Vector(138, 330));
    new Vector(161, 10),
    new Vector(561, 111),
    new Vector(890, 254),
    new Vector(1088, 254),
    new Vector(1152, 130),
    new Vector(1186, 55),
    new Vector(1230, 21)

// Rendering code
// Do stuff here
smoothline.line(context, 16);
// Do stuff here

Over the next few months if I can possibly manage it I want to implement a bunch of other useful algorithms in order to build up a library of code that I can just drop into a project and use. Suggestions for the next algorithm are welcome!

A first look a fractals - Shapes

My fractal shape generator.

Recently I took a little look at fractals, and in order to get my head around the recursive nature of drawing fractals, I wrote a small demo that draws a fractal like thing with shapes. It starts with a triangle, and draws a square at each corner. Then at the corner of each square, it draws a pentagon, and so the pattern continues. I thought it looked interesting, so I decided to share it here.

You can find it here: fractal shapes

You can also find it under the labs section of my homepage.

If anyone is interested in a more detailed explanation of how it works, I'd be happy to write a blog post about it. Comment below if you would like one.

Easy Bezier Curves on the HTML5 Canvas

This is a follow up post to the vector.js post that I made last week, and depends on the vector class I released then. Please take a look at that post first.

Last week, I released a simple Ecmascript 6 vector class that I wrote. It's mildly interesting on its own, but this post is the real reason I wrote that other one. Using that vector class, I then went ahead and wrote my own bezier curve class, that supports an arbitrary number of control points. Before I continue, here's the code:

(Gist, Raw)

I was surprised by how easy the bezier curve algorithm was to implement. Basically, you loop over all your control points, finding the point that lies in a specific percentage of the distance between the current point and the next one. You then repeat this process until you have just a single point remaining. This results in a smooth curve that is skewed towards all of the given control points.

In my implementation, I did it recursively, with all the magic happening in the interpolate() function. It performs the above algorithm given a time between 0 and 1, and spits out the interpolated value. I called it a time here because bezier curves are often used to smooth out animations, and I travel along the line in the curve() function when applying it to the given canvas rendering context.

To use it, you first create an instance like so:

var bz = new BezierCurve([
    new Vector(38, 41),
    new Vector(96, 302),
    new Vector(807, 12)

Then, in your rendering function, you can ask your new bezier curve to add itself to any given canvas rendering context like this:

// ...

// ...
bz.curve(context, 32);
// ...

// ...

The segmenting algorithm in action.

The second argument in the curve() call above is the number of segments to use when rendering. This tells the bezier curve class how many different points along the line it should calculate. More segments make it smoother, but will consume more processing power when first calculated. Pick just enough that you can't tell that the bezier curve is made up of lines - this is different for every curve.

I added a caching function to it too, so if you call the curve() function with the same number of segments more than once, it uses the interpolated values it calculated previously instead of calculating them all over again. This isn't the case if you call it with a different number of segments each time, however. If you want to do this, I suggest that you create a new instance for each different segment number that you need.

That concludes this post on my own bezier curve class. It's a little bit buggy in places (see the gif above), but I haven't managed to track down the issue. It should work fine for most purposes, though. If you do manage to spot the mistake, please let me know!

Update 24th January 2016: I've replaced the original code with an embedded version of the gist in order to keep it up to date, since I've revised it slightly sinec writing this blog post.

Easy circles on the canvas with context.ellipse()

Ripples made using context.ellipse().

A while ago I was building a family tree viewer for an ACW (Assessed CourseWork) at University. Part of this ACW involved drawing faces inside ovals and using circles for various things. The suggested method here was using bezier curves (more on this on Wednesday), but I found another (much easier!) way of doing it that I thought others would find useful, so I am posting about it here.

Instead of using context.bezierCurveTo() and battling with control points, you can just use context.ellipse to add either a circle or an ellipse to the current path. Here's an extract fomr the wonderful MDN:


void ctx.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise);


Parameter Explanation
x The x axis of the coordinate for the ellipse's center.
y The y axis of the coordinate for the ellipse's center.
radiusX The ellipse's major-axis radius.
radiusY The ellipse's minor-axis radius.
rotation The rotation for this ellipse, expressed in radians.
startAngle The starting point, measured from the x axis, from which it will be drawn, expressed in radians.
endAngle The end ellipse's angle to which it will be drawn, expressed in radians.
anticlockwise Optional. An Boolean which, if true, draws the ellipse anticlockwise (counter-clockwise), otherwise in a clockwise direction.

For example, here's how you'd draw a 100x200 red ellipse at (0, 0):

function renderEllipse(context)
    context.fillStyle = "#ff3300";
    context.ellipse(0, 0, 100, 200, 0, 0, Math.PI * 2, false);

The startAngle and endAngle functions work the same as the context.arc() command - they let you draw just part of a circle or ellipse instead of a full one. In the example above, I'm drawing a full one by starting at 0 and finishing at (260°).

I've built a simple 'ripples' demo that demonstrates context.ellipse() in action. Click anywhere on the screen to create a ripple. The background is made with a few quick radial gradiants that fade from a colour into transparency.

Art by Mythdael