STRd6

Useful JavaScript Game Extensions: Array#shuffle

Daniel X Moore — Mon, 06 Sep 2010 08:08:47 +0000

Part 7/256

Shuffling is important, especially in card games.

/**
 * Returns a new array with the elements all shuffled up.
 *
 * @returns A new array that is randomly shuffled.
 * @type Array
 */
Array.prototype.shuffle = function() {
  var shuffledArray = [];
 
  this.each(function(element) {
    shuffledArray.splice(rand(shuffledArray.length + 1), 0, element);
  });
 
  return shuffledArray;
};

Notice how building on the previous components of rand and each makes this method much easier to write. You’ll find that when you surround yourself with great APIs things constantly become easier and easier, whereas when you are surrounded with terrible APIs things become harder and harder.

Using Google Font API to Render Inconsolata in HTML5 Canvas

Daniel X Moore — Sun, 05 Sep 2010 07:56:33 +0000

In Contrasaurus we wanted some cooler fonts to add some extra ambiance to the game. I knew that adding a custom font from Google Font API was easy for classic HTML elements, but would it be easy for HTML5 Canvas elements? 5 minutes later I knew the answer… Yes!

// In the  tag
<link href='http://fonts.googleapis.com/css?family=Inconsolata' rel='stylesheet' type='text/css'>
 
// In your js code
context.font = "bold 1.2em 'Inconsolata'";

Useful JavaScript Game Extensions: Array#each

Daniel X Moore — Wed, 01 Sep 2010 21:16:24 +0000

Welcome to the nether realm of JavaScript extensions… things that should exist and sometimes kind of do, but with a different name and an inconsiderate API.

Part 6 of 256 Useful JavaScript Extensions Array#each.

/**
 * Call the given iterator once for each element in the array,
 * passing in the element as the first argument, the index of 
 * the element as the second argument, and this array as the
 * third argument.
 *
 * @param {Function} iterator Function to be called once for 
 * each element in the array.
 * @param {Object} [context] Optional context parameter to be 
 * used as `this` when calling the iterator function.
 *
 * @returns `this` to enable method chaining.
 */
Array.prototype.each = function(iterator, context) {
  if(this.forEach) {
    this.forEach(iterator, context);
  } else {
    var len = this.length;
    for(var i = 0; i < len; i++) {
      iterator.call(context, this[i], i, this);
    }
  }
 
  return this;
};

You’ll notice that this method makes use of the possibly existing Array#forEach method if it exists. In fact it is almost an alias of it, but since forEach always returns undefined like a jerk, we need to wrap it and return the object for chaining like a good citizen. Also, who wants to always be writing forEach, why not just each? Yeah… I like this.

// Example:
 
var people = [{name: "David"}, {name: "Joe"}, {name: "Gandalf"}];
 
// Greet each person by name
people.each(function(person) {
  alert("Hi " + person.name + "!");
});

Useful JavaScript Extensions: Number#times

Daniel X Moore — Tue, 31 Aug 2010 19:24:29 +0000

Part 5/256

For loops… I hate them so much. Fortunately, a well established functional iteration convention is the Number#times method.

/**
 * Calls iterator the specified number of times, passing in a number of the 
 * current iteration as a parameter. The number will be 0 on first call, 1 on 
 * second call, etc. 
 * 
 * @param {Function} iterator The iterator takes a single parameter, the number 
 * of the current iteration.
 * @param {Object} [context] The optional context parameter specifies an object
 * to treat as this in the iterator block.
 * 
 * @returns The number of times the iterator was called.
 */
Number.prototype.times = function(iterator, context) {
  for(var i = 0; i < this; i++) {
    iterator.call(context, i);
  }
  return i;
}

This hides the inner workings of the iteration from the calling code so there’s no need to keep track of an external dummy iterator variable if you don’t want to.

var n = 3;
 
// Greets you three times, with respect
n.times(function() {
  alert("O HAI!");
});
 
// logs: 0, 1, 2
n.times(function(i) {
  console.log(i);
});

Useful JavaScript Game Extensions: Array#remove

Daniel X Moore — Sat, 28 Aug 2010 21:16:19 +0000

Part 4: Array#remove

JavaScript Arrays are missing some very common, very useful functions. One of those is the remove method. We want to be able to say “Hey you, array, remove this object from yourself! Now!!” But our poor JS array’s don’t know how. They can barely remove elements from specific indices, let alone a specified object. Well no longer! Now they’ll do what we say.

/**
 * Remove the first occurance of the given object from the array if it is
 * present.
 *
 * @param {Object} object The object to remove from the array if present.
 * @returns The removed object if present otherwise undefined.
 */
Array.prototype.remove = function(object) {
  var index = this.indexOf(object);
  if(index >= 0) {
    return this.splice(index, 1)[0];
  } else {
    return undefined;
  }
};

By building off of the Array‘s built in methods we can keep this code very short. We find the first occurrence of the specified object using indexOf, then we remove and return it using splice. If it wasn’t found we return undefined instead.

// An illustrative test suite
 
test("Array#remove", function() {
  ok([1,2,3].remove(2) === 2, "[1,2,3].remove(2) === 2");
  ok([1,3].remove(2) === undefined, "[1,3].remove(2) === undefined");
  ok([1,3].remove(3) === 3, "[1,3].remove(3) === 3");
 
  var array = [1,2,3];
  array.remove(2);
  ok(array.length === 2, "array = [1,2,3]; array.remove(2); array.length === 2");
  array.remove(3);
  ok(array.length === 1, "array = [1,3]; array.remove(3); array.length === 1");
});

John Resig has another take on Array#remove, remove by index. You may want to take a look at that as well, though for me it feels more natural to remove by specified object rather than by specified index.

Useful JavaScript Game Extensions: Array#rand

Daniel X Moore — Fri, 27 Aug 2010 17:51:16 +0000

Part 3 of 256.

/**
 * Randomly select an element from the array. The array remains unmodified.
 *
 * @returns A random element from an array, or undefined if the array is empty.
 */
Array.prototype.rand = function() {
  return this[rand(this.length)];
};

Building on the last installment of a global rand method, we can easily extend Array to provide simple random element selection.

// Example:
["rock", "paper", "scissors"].rand()

Selecting options from a loot table, or random AI actions is now wonderfully easy. With all these extensions the theme is the same, start with the best interface for the programmer and extend what you must to make it happen.

Useful JavaScript Game Extensions: rand

Daniel X Moore — Thu, 26 Aug 2010 16:56:34 +0000

Part 2 of my 256 part series: Useful JavaScript Game Extensions!

/**
 * Generate uniformly distributed random numbers.
 *
 * @param {Number} [n]
 * @returns A Random integers from [0, n) if n is given, otherwise a random float
 * between 0 and 1.
 * @type Number
 */
function rand(n) {
  if(n !== undefined) {
    return Math.floor(Math.random() * n);
  } else {
    return Math.random();
  }
}

Some games make use of random numbers… a lot. So when choosing the best interface it is important to keep that in mind. Often times uniform distributions are the way to go, such as when selecting from an array, or rolling a six sided die. If one often has need of a variety of random distributions then having different methods live in a Random namespace would probably be best. For simple, everyday use a little rand(6) is very convenient.

Useful JavaScript Game Extensions: Clamp

Daniel X Moore — Wed, 25 Aug 2010 19:53:52 +0000

Part 1 of my new 256 part series on simple JavaScript extensions to make game programming easy and fun!

/**
 * Returns a number whose value is limited to the given range.
 *
 * Example: limit the output of this computation to between 0 and 255
 * (x * 255).clamp(0, 255)
 *
 * @param {Number} min The lower boundary of the output range
 * @param {Number} max The upper boundary of the output range
 * @returns A number in the range [min, max]
 * @type Number
 */
Number.prototype.clamp = function(min, max) {
  return Math.min(Math.max(this, min), max);
};

Note that this extends the behavior of the Number class. Some may consider it poor form to “mess with” the JS built-ins, but I consider it poor form to expose a worse than necessary interface to the programmer. Compare:

// Namespace?
STRd6.Util.clamp(x * 255, 0, 255);
 
// global function clamp?
clamp(x * 255, 0, 255);
 
// Clean, simple and object oriented!
(x * 255).clamp(0, 255);

Stay tuned for the next 255 parts of the series!

Matrix.js 1.0.1 Released

Daniel X Moore — Tue, 24 Aug 2010 02:16:45 +0000

Thoroughly documented, tested, and minifies very small (1.4k), this is the best release yet!

Observe the sweetness:

  // Rotate 90 degrees
  var matrix = Matrix.rotation(Math.PI / 4);
 
  // Scale and move
  var finalTransform = matrix.scale(1/2).translate(125, 175);
 
  canvas.withTransform(finalTransform, function() {
    // Draw a circle or whatever in the transformed coordinates
    // canvas.fillCircle(0, 0, 50);
  });

A dinosaur covered in weapons will save the world, and that’s all I need to know

Daniel X Moore — Sat, 14 Aug 2010 08:02:02 +0000

Lock and load!