kka-ga

v0.0.5

Published

3 years ago

The world's tiniest, cutest and funnest game engine

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bsorrentino

Typescript Javascript Game Engine

Goal

Make the amazing tiny, cute and friendly Ga HTML5 game engine compliant with typescript

Getting Started

install package

npm i kka-ga

import types in your typescript source

/// <reference types="kka-ga" />

import ga javascript assets directly in your HTML

<!doctype html> 
<meta charset = "utf-8"> 
<title>MY GAME</title>
<body>

<script src="node_modules/kka-ga/src/ga.js" ></script>
<script src="node_modules/kka-ga/src/plugins.js" ></script>

</body>

Examples

In the Examples folder there are a lot of typescript samples useful to better understand the Ga features. To start them execute the following command in your shell:

npx parcel serve ./examples/index.html --open

Tutorials

In the Tutorials folder there are the original ones translated into typescript To start them execute the following command in your shell:

npx parcel serve ./tutorials/index.html --open

Ga

"Ga!"

- A baby's exclamation of surprise.

Ga is a tiny, cute and friendly system for making HTML5 games or any other kind interactive media. You can use it to make any kind of 2D action game you can imagine, with unbelievably tiny file sizes (under 6.5k!)

Take a look at the feature list and the examples folder to get started. Keep scrolling, and you'll find a complete beginner's tutorial ahead. If you've never made a game before, the tutorials are the best place to start.

Features

Here's Ga's core feature list:

All the most important sprites you need: rectangles, circles, lines, text, image sprites and animated "MovieClip" style sprites. You can make any of these sprites with one only line of code. You can also create your own custom sprite types.
A complete scene graph with nested child-parent hierarchies (including a stage, and addChild/removeChild methods), local and global coordinates, depth layers, and rotation pivots.
group sprites together to make game scenes.
A game loop with a user-definable fps and fully customizable and drop-dead-simple game state manager. pause and resume the game loop at any time.
Tileset (spritesheet) support using frame and filmstrip methods to make sprites using tileset frames.
Built-in texture atlas support for the popular Texture Packer format. Use a sprite's setTexture method if you want to change a sprite's image source while the game is running
A keyframe animation and state manager for sprites. Use show to display a sprite's image state. Use play or playSequence to play a sequence of frames (in a loop if you want to). Use show to display a specific frame number. Use fps to set the frame rate for sprite animations which is independent from the game's frame rate.
Interactive button sprites with up, over and down states.
Any sprite can be set as interactive to receive mouse and touch actions. Intuitive press, release, over, out and tap methods for buttons and interactive sprites.
Easy-to-use keyboard key bindings. The arrow and space keys are built-in, and you can easily define your own with the keyboard method.
A built-in universal pointer that works with both the mouse and touch. Assign your own custom press, release and tap methods or use any of the pointer's built-in properties: isUp, isDown, tapped, x and y. Define as many pointers as you need for multi-touch.
Conveniently position sprites relative to other sprites using putTop, putRight, putBottom, putLeft and putCenter.
A universal asset loader to pre-load images, fonts, sounds and JSON data files. All popular file formats are supported. You can load new assets into the game at any time.
An optional load state that lets you run actions while assets are loading. You can use the load state to add a loading progress bar.
A fast and focused canvas-based rendering engine.
A sophisticated game loop using a fixed timestep with variable rendering and sprite interpolation. That means you get butter-smooth sprite animations at any framerate.
A plugins.js file full of extra tools.
A compact and powerful "Haiku" style API that's centered on shallow, composable components. Get more done writing less code.
Ga is totally hackable. Overwrite any of its default methods or objects with your own at compile or run time.
Yes, Ga is mobile friendly!
Yes, the core ga.js engine is less than 6.5k minified and zipped! That makes Ga the world's smallest, most light-weight full featured game engine. It's all you need to start making any any 2D action, puzzle or strategy game.

And the coolest part? If you were alone on a desert island with only a solar powered laptop, an unlimited supply of coconuts, and a copy of ga.js you could recreate the entire history of 2D video games, from SpaceWar! to Flappy Bird. And all of it would fit on a 3.5 inch floppy disk.

The plugins

But there's more! Ga comes with a plugins.js file that includes a huge number of useful tools for making games. You can use as many or as few of these tools as you want to. Here are some of the goodies you'll find in plugins.js:

Import and play sounds using a built-in WebAudio API sound manager. Control sounds with play, pause, stop, restart, playFrom, fadeIn and fadeOut methods. Change a sound's volume and pan.
Generate your own custom sound effects from pure code with the versatile soundEffect method.
Shake sprites or the screen with shake.
Tween functions for sprite and scene transitions: slide, fadeIn, fadeOut, pulse, breathe, wobble, strobe and some useful low-level tweening methods to help you create your own custom tweens.
Make a sprite follow a connected series of waypoints with walkPath and walkCurve.
A handful of useful convenience functions: followEase, followConstant, angle, distance, rotateAroundSprite, rotateAroundPoint, wait, randomInt, randomFloat, contain and outsideBounds.
A fast, universal hit method that handles collision testing and reactions (blocking and bounce) for all types of sprites. Use one collision method for everything: rectangles, circles, points, and arrays of sprites. Easy!
A companion suite of lightweight, low-level 2D geometric collision methods.
A loading progress bar for game assets.
Make sprites shoot things with shoot.
Easily plot sprites in a grid formation with grid.
Use a tilingSprite to easily create a seamless scrolling background.
Tiled Editor support using makeTiledWorld. Design your game in Tiled Editor and access all the sprites, layers and objects directly in your game code. It's an extremely fun, quick and easy way to make games.
A versatile, hitTestTile method that handles all the collision checking you'll need for tile-based games. You can use it in combination with the any of the 2D geometric collision methods for optimized broadphase/narrowphase collision checking if you want to.
A particleEffect function for creating all kinds of particle effects for games. Use the emitter function to create a constant stream of particles.
Use updateMap to keep a tile-based world's map data array up-to-date with moving sprites.
Create a worldCamera that follows sprites around a scrolling game world.
Use scaleToWindow to make the game automatically scale to its maximum size and align itself for the best fit inside the browser window. Use enterFullscreen to make the browser enter full screen mode, and exitFullscreen to exit full screen mode.

To use the plugins, just copy/paste the code you want to use from plugins.js into your game. Or, if you're not worried about the extra size, just link the whole thing; it's really tiny anyway!

If you want to get fancy, you can alternatively create your own custom.js file that contains a small custom sub-set of the plugins you want to use for your game. Your custom.js file can load at compile time, so it's ready to use before your game code runs. (See the plugins.js file for instructions on how to do this).

Coming soon...

Tiled Editor isometric maps support.
Many more examples including complete game prototypes.
Additional documentation, examples, and tutorials.

Ga's philosophy and technical constraints

The ga.js core game engine file can't ever be bigger that 6.5k minified and zipped. Yes, 6.5k! This makes it suitable for making games for micro game competitions, like js13k. This absurdly low overhead means you can drop a full-featured 2D action game into a web page and have it load and play almost instantly. But, more importantly, this constraint also discourages feature-creep and keeps the engine lean and focused.
The API has to be fun, intuitive and expressive with as little boilerplate code as possible. Game designers should be free to explore their imaginations without tripping over a tangled and messy API. Less typing, Less thinking!
The source code must be easily readable and comment-rich so that everyone can learn from it. It should also be architecturally flat so that anyone can rip it apart and easily drop it into something else.
For the same reasons, all the source code must be hand-written written from scratch without any 3rd party dependencies (external libraries.)
Any special features, like Tiled Editor support, can be added to the plugins.js file, so that game developers can pick and choose a minimal custom set of components they want for specific games without bloating the core engine.

Minifying, crushing and compressing

The Ga repository doesn't include the minified and compressed version of the source code, because you should probably optimize that yourself. I recommend first minifying the code using with Google Closure Compiler (Simple mode only) or UglifyJS2. Google Closure will give you best minification, and Ga's source code is optimized for it.

Then, zip it. I recommend gzip.

For more aggressive optimization, you could further try running the minified code through JSCrush. Although it sometimes makes things worse rather than better - you'll have to test it with your code.

Note: If you're using Google Closure Compiler from the command line, set the --language_in flag to ECMASCRIPT5, like this:

java -jar ~/compiler.jar --language_in=ECMASCRIPT5 --js ga.js --js_output_file ga.min.js

Contributions and Licencing

It's Ga's ambition to be the world's tiniest, cutest and funnest game engine. Please help! If you find something that's bad, please help to fix it. If you find something good, please help to make it better. Ga welcomes any and all contributions!

+1 Bonus Points for removing code and simplifying the architecture. +2 Bonus Points for making the code easier to understand. The aim of this project is to discover the smallest universal set of reusable components required to make the widest variety of games possible with the least amount of code. What is the fundamental alphabet, or the primary colours, of game design? That's what we're searching. Can you help?

Checkout the dev branch to make experimental changes and bug fixes, and we'll merge it with the master branch when we can confirm that everything is stable. Make sure that any code changes you make are compatible with Google Closure Compiler.

Please feel free to PR (Pull Request) any bug fixes and minor code improvements and optimizations. Any changes to the user-facing public API will need to be discussed in the Issues first. If we make any public API changes, we'll need to commit to updating all affected example and tutorial files as well. Also, any major changes to the engine will need to be discused too.

Coding style: Unconventionally, Ga uses functional composition patterns (the module pattern and mixins) for object creation instead of inheritance. Why? It's really just an experiment in coding like that. It also means the code becomes a little more compact.

Licensing? Ga is vehemently unlicenesed. That means its freer than free.

It's like a pebble. You can pick it up and throw into the sea.

Hexi

Do you like Ga, but wished that it had a powerful WebGL renderer and a gazillion other features that you will probably never use? Then checkout Ga's sister game engine: Hexi. It uses almost exactly the same API as Ga, but is built on top of the latest stable version of the powerful, full-featured Pixi renderer. What that means is that you can prototype your games for js13k, and port 99% of that code unchanged into Hexi to build your prodction version. If you don't care about small file sizes, and need a highly flexible, mobile-optimized and production-ready game engine using the world's most streamlined API, then check out Hexi!

Tutorials

How do you make a video game? These tutorials will show you how.

But first, you should have a reasonable understanding of HTML and JavaScript. You don't have to be an expert, just an ambitious beginner with an eagerness to learn. If you don't know HTML and JavaScript, the best place to start learning it is this book:

Foundation Game Design with HTML5 and JavaScript

I know for a fact that it's the best book, because I wrote it :)

There are also some good internet resources to help get you started:

Khan Academy: Computer Programming

Code Academy: JavaScript

Ok, got it? Do you know what JavaScript variables, functions, arrays and objects are and how to use them? Good, then read on!

Treasure Hunter

The first game we're going to make is a simple object collection and enemy avoidance game called Treasure Hunter. Open the file 01_treasureHunter.html in a web browser. (You'll find it in Ga's tutorials folder, and you'll need to run it in a webserver). If you don't want to bother setting up a webserver, use a text-editor like Brackets that will launch one for you automatically (see Brackets' documentation for this feature).

(Follow the link in the image above to play the game.) Use the keyboard to move the explorer (the blue square), collect the treasure (the yellow square), avoid the monsters (the red squares) and reach the exit (the green square.) Yes, you have to use your imagination - for now.

Don't be fooled by it's apparent simplicity. Treasure Hunter contains everything a video game needs:

Interactivity
Collision
Sprites
A game loop
Scenes
game logic
"Juice" (in the form of sounds)

(What's juice? Watch this video and read this article to learn about this essential game design ingredient.)

If you can make a simple game like Treasure Hunter, you can make almost any other kind of game. Yes, really! Getting from Treasure Hunter to Skyrim or Zelda is just a matter of lots of small steps; adding more detail as you go. How much detail you want to add is up to you.

In the first stage of this tutorial you'll learn how the basic Treasure Hunter game was made, and then we'll add some fun features like images and character animation that will give you a complete overview of how the Ga game engine works.

If you're an experienced game programmer and quick self-starter, you might find the code in Ga's examples folder to be a more productive place to start learning - check it out. The fully commented code in the examples folder also details specific, and advanced uses of features, that aren't covered in these tutorials. When you're finished working through these tutorials, the examples will take you on the next stage of your journey.

Setting up the HTML container page

Before you can start programming in JavaScript, you need to set up a minimal HTML container page. The HTML page loads ga.js and plugins.js which are the two files you need to use all of Ga's features. You'll write all your game code inside the last pair of <script> tags before the closing <body> tag.

<!doctype html>
<meta charset="utf-8">
<title>Treasure hunter</title>
<body>
<!-- Import the Ga game engine files -->
<script src="../ga.js"></script>
<script src="../plugins.js"></script>
<script>

//All of your game code will go here

</script>
</body>

This is the minimum amount of HTML code you need for a valid HTML5 document.

Initializing the Ga engine

The next step is to write some JavaScript code that initializes and starts the Ga game engine, according to some parameters that you specify. This bit of code below initializes a game with a screen size of 512 by 512 pixels. It also pre-loads the chimes.wav sound file from the sounds folder.

var g = ga(
  512, 512, setup,
  [
    "sounds/chimes.wav"
  ]
);

//Start the Ga engine.
g.start();

You can see that the result of the ga function is being assigned to an variable called g.

var g = ga(

Now, whenever you want to use any of Ga's custom methods or objects in your game, just prefix it with g. (You don't have to use g to represent the game engine, you can use any variable name you want. g is just nice, short, and easy to remember; g = "game".)

In this example Ga creates a canvas element with a size of 512 by 512 pixels. That's specified by the first two arguments:

512, 512, setup,

The third argument, setup, means that as soon as Ga is initialized, it should look for and run a function in your game code called setup. Whatever code is in the setup function is entirely up to you, and you'll soon see how you can used it to initialize a game. (You don't have to call this function setup, you can use any name you like.)

Ga lets you pre-load game assets with an optional 4th argument, which is an array of file names. In this first example, you only need to preload one file: chimes.wav You can see that the full file path to chimes.wav is listed as a string in the initialization array:

[
  "sounds/chimes.wav"
]

You can list as many game assets as you like here, including images, fonts, and JSON files. Ga will load all these assets for you before running any of the game code.

The last thing you need to do is call Ga's start method.

g.start();

This is the switch that turns the Ga engine on.

Define your "global" variables

After Ga has been started, declare all the variables that your game functions will need to use.

var dungeon, player, treasure, enemies, chimes, exit,
    healthBar, message, gameScene, gameOverScene;

Because they're not enclosed inside a function, these variables are "global" in the sense that you can use them across all of your game functions. (They're not necessarily "global" in the sense that they inhabit the global JavaScript name-space. If you want to ensure that they aren't, wrap all of your JavaScript code in an enclosing immediate function to isolate it from the global space.

Initialize your game with a setup function

As soon as Ga starts, it will look for and run a function in your game code called setup (or whatever other name you want to give this function.) The setup function is only run once, and lets you perform one-time setup tasks for your game. It's a great place to create and initialize objects, create sprites, game scenes, populate data arrays or parse loaded JSON game data.

Here's an abridged, birds-eye view of the setup function in Treasure Hunter, and the tasks that it performs.

function setup() {
  //Set the canvas border and background color
  //Create the `chimes` sound object
  //Create the `gameScene` group
  //Create the `exit` door sprite
  //Create the `player` sprite
  //Create the `treasure` sprite
  //Make the enemies
  //Create the health bar
  //Add some text for the game over message
  //Create a `gameOverScene` group 
  //Assign the player's keyboard controllers

  //set the game state to `play`
  g.state = play;
}

The last line of code, g.state = play is perhaps the most important because it starts the play function. The play function runs all the game logic in a loop. But before we look at how that works, let's see what the specific code inside the setup function does.

Customizing the canvas

The first two lines in the setup function give the canvas a black dashed border and set its background color to white.

g.canvas.style.border = "1px black dashed";
g.backgroundColor = "white";

Here's the effect these two lines have on the Ga canvas:

Treasure Hunter

Ga uses an ordinary 2D canvas element to display the game graphics, and you can access it in your code at any time with g.canvas. You can modify it with any ordinary HTML/CSS properties.

Creating the `chimes` sound object

You'll remember from the code above that we preloaded a sound file into the game called chimes.wav. Before you can use it in your game, you have to make a reference to it using Ga's sound method, like this:

chimes = g.sound("sounds/chimes.wav");

Alternatively, you can access any assets that you've loaded via Ga's assets object, like this:

g.assets["sounds/chimes.wav"]

Any assets that you've preloaded like this are accessible in the assets object.

Many assets that you might want to use, like sounds, fonts, and JSON files, can only be loaded by the browser if your code is running inside a web server. If you're trying to load or use an asset, and the browser is giving your a strange security related error message, check to make sure that the web server is initialized.

Creating game scenes

Ga has a useful method called group that lets you group game objects together so that you can work with them as one unit. Groups are used for grouping together special objects called sprites (which you'll learn all about in the next section.) But they're also used for making game scenes.

Treasure Hunter uses two game scenes: gameScene which is the main game, and gameOverScene which is displayed when the game is finished. Here's how the gameScene is made using the group method:

gameScene = g.group();

After you've made the group, you can add sprites (game objects) to the gameScene, using the addChild method.

gameScene.addChild(anySprite);

Or, you can add multiple sprites at one time with the add method, like this:

gameScene.add(spriteOne, spriteTwo, spriteThree);

Or, if you prefer, you can create the game scene after you've made all the sprites, and group all the sprites together with one line of code, like this:

gameScene = g.group(spriteOne, spriteTwp, spriteThree);

You'll see a few different examples of how to add sprites to groups in the examples ahead.

But what are sprites, and how do you make them?

Making sprites

Sprites are the most important elements in any game. Sprites are just graphics (shapes or images) that you can control with special properties. Everything you can see in your games, like game characters, objects and backgrounds, are sprites. Ga lets you make 5 kinds of basic sprites: rectangle, circle, line, text, and sprite (an image-based sprite). You can make almost any 2D action game with these basic sprite types. (If they aren't enough, you can also define your own custom sprite types.) This first version of Treasure Hunter only uses rectangle sprites. You can make a rectangle sprite like this:

var box = g.rectangle(
  widthInPixels, 
  heightInPixels, 
  "fillColor", 
  "strokeColor", 
  lineWidth, 
  xPosition, 
  yPosition
);

You can use Ga's circle method to make a circular shaped sprite:

var ball = g.circle(
  diameterInPixels, 
  "fillColor", 
  "strokeColor", 
  lineWidth,
  xPosition, 
  yPosition 
);

It's often useful to prototype a new game using only rectangle and circle sprites, because that can help you focus on the mechanics of your game in a pure, elemental way. That's what this first version of Treasure Hunter does. Here's the code from the setup function that creates the exit, player and treasure sprites.

//The exit door
exit = g.rectangle(48, 48, "green");
exit.x = 8;
exit.y = 8;
gameScene.addChild(exit);

//The player sprite
player = g.rectangle(32, 32, "blue");
player.x = 68;
player.y = g.canvas.height / 2 - player.halfHeight;
gameScene.addChild(player);

//Create the treasure sprite
treasure = g.rectangle(16, 16, "gold");

//Position the treasure next to the right edge of the canvas
treasure.x = g.canvas.width - treasure.width - 32;
treasure.y = g.canvas.height / 2 - treasure.halfHeight;

//Create a `pickedUp` property on the treasure to help us figure
//out whether or not the treasure has been picked up by the player
treasure.pickedUp = false;

//Add the treasure to the gameScene
gameScene.addChild(treasure);

Notice that after each sprite is created, it's added to the gameScene using addChild. Here's what the above code produces:

Treasure Hunter

Let's find out a little more about how these sprites are positioned on the canvas.

Positioning sprites

All sprites have x and y properties that you can use to precisely position sprites on the canvas. The x and y values refer to the sprites' pixel coordinates relative to the canvas's top left corner. The top left corner has x and y values of 0. That means any positive x and y values you assign to sprites will position them left (x) and down (y) relative to that corner point. For example, Here's the code that positions the exit door (the green square).

exit.x = 8;
exit.y = 8;

You can see that this code places the door 8 pixel to the right and 8 pixels below the canvas's top left corner. Positive x values position sprites to the right of the canvas's left edge. Positive y values position them below the canvas's top edge.

Sprites also have width and height properties that tell you their width and height in pixels. If you need to find out what half the width or half the height of a sprite is, use halfWidth and halfHeight.

Ga also has a some convenience methods that help you quickly position sprites relative to other sprites: putTop, putRight, putBottom, putLeft and putCenter. For example, here are the lines from the code above that position the treasure sprite (the gold box). The code places the treasure 26 pixels to the left of the canvas's right edge, and centers it vertically.

treasure.x = g.canvas.width - treasure.width - 32;
treasure.y = g.canvas.height / 2 - treasure.halfHeight;

That's a lot of complicated positioning code to write. Instead, you could use Ga's built-in putCenter method to achieve the same effect like this:

g.stage.putCenter(treasure, 220, 0);

What is the stage? It's the root container for all the sprites, and has exactly the same dimensions as the canvas. You can think of the stage as a big, invisible sprite, the same size as the canvas, that contains all the sprites in your game, as well as any containers those sprites might be grouped in (Like the gameScene). putCenter works by centering the treasure inside the stage, and then offsetting its x position by 220 pixels. Here's the format for using putCenter:

anySprite.putCenter(anyOtherSprite, xOffset, yOffset);

You can use the other put methods in the same way. For example, if you wanted to position a sprite directly to the left of another sprite, without any offset, you could use putLeft, like this:

spriteOne.putLeft(spriteTwo);

This would place spriteTwo directly to the left of spriteOne, and align it vertically .You'll see many examples of how to use these put methods throughout these tutorials.

Assigning dynamic properties

Before we continue, there's one small detail you need to notice. The code that creates the sprites also adds a pickedUp property to the treasure sprite:

treasure.pickedUp = false;

You'll see how we're going to use treasure.pickedUp later in the game logic to help us determine the progress of the game. You can dynamically assign any custom properties or methods to sprites like this, if you need to.

Creating the enemy sprites

There are 6 enemies sprites (red squares) in Treasure Hunter. They're spaced evenly horizontally but but have random initial vertical positions. All the enemies sprites are created in a for loop using this code in the setup function:

//Make the enemies
var numberOfEnemies = 6,
    spacing = 48,
    xOffset = 150,
    speed = 2,
    direction = 1;

enemies = [];

//Make as many enemies as there are `numberOfEnemies`
for (var i = 0; i < numberOfEnemies; i++) {

  //Each enemy is a red rectangle
  var enemy = g.rectangle(32, 32, "red");

  //Space each enemey horizontally according to the `spacing` value.
  //`xOffset` determines the point from the left of the screen
  //at which the first enemy should be added.
  var x = spacing * i + xOffset;

  //Give the enemy a random y position
  var y = g.randomInt(0, g.canvas.height - enemy.height);

  //Set the enemy's direction
  enemy.x = x;
  enemy.y = y;

  //Set the enemy's vertical velocity. `direction` will be either `1` or
  //`-1`. `1` means the enemy will move down and `-1` means the enemy will
  //move up. Multiplying `direction` by `speed` determines the enemy's
  //vertical direction
  enemy.vy = speed * direction;

  //Reverse the direction for the next enemy
  direction *= -1;

  //Push the enemy into the `enemies` array
  enemies.push(enemy);

  //Add the enemy to the `gameScene`
  gameScene.addChild(enemy);
}

Here's what this code produces:

Treasure Hunter

The code gives each of the enemies a random y position with the help of Ga's randomInt method:

var y = g.randomInt(0, g.canvas.height - enemy.height);

randomInt will give you a random number between any two integers that you provide in the arguments. (If you need a random decimal number, use randomFloat instead).

All sprites have properties called vx and vy. They determine the speed and direction that the sprite will move in the horizontal direction (vx) and vertical direction (vy). The enemies in Treasure Hunter only move up and down, so they just need a vy value. Their vy is speed (2) multiplied by direction (which will be either 1 or -1).

enemy.vy = speed * direction;

If direction is 1, the enemy's vy will be 2. That means the enemy will move down the screen at a rate of 2 pixels per frame. If direction is -1, the enemy's speed will be -2. That means the enemy will move up the screen at 2 pixels per frame.

After the enemy's vy is set, direction is reversed so that the next enemy will move in the opposite direction.

direction *= -1;

You can see that each enemy that's created is pushed into an array called enemies.

enemies.push(enemy);

Later in the code you'll see how we'll access all the enemies in this array to figure out if they're touching the player.

The health bar

You'll notice that when the player touches one of the enemies, the width of the health bar at the top right corner of the screen decreases.

Treasure Hunter

How was this health bar made? It's just two rectangle sprites at the same position: a black rectangle behind, and a green rectangle in front. They're grouped together to make a single compound sprite called healthBar. The healthBar is then added to the gameScene.

//Create the health bar
var outerBar = g.rectangle(128, 16, "black"),
    innerBar = g.rectangle(128, 16, "yellowGreen");

//Group the inner and outer bars
healthBar = g.group(outerBar, innerBar);

//Set the `innerBar` as a property of the `healthBar`
healthBar.inner = innerBar;

//Position the health bar
healthBar.x = g.canvas.width - 148;
healthBar.y = 16;

//Add the health bar to the `gameScene`
gameScene.addChild(healthBar);

You can see that a property called inner has been added to the healthBar. It just references the innerBar (the green rectangle) so that it will be convenient to access later.

healthBar.inner = innerBar;

You don't have to do this; but, hey why not! It means that if you want to control the width of the innerBar, you can write some smooth code that looks like this:

healthBar.inner.width = 30;

That's pretty neat and readable, so we'll keep it!

The game over scene

If the player's health drops to zero, or the player manages to carry the treasure to the exit, the game ends and the game over screen is displayed. The game over scene is just some text that displays "You won!" or "You lost!" depending on the outcome.

Treasure Hunter

How was this made? The text is made with a text sprite.

var anyText = g.text(
  "Hello!", "CSS font properties", "fillColor", xPosition, yPosition
);

The first argument, "Hello!" in the above example, is the text content you want to display. Use the content property to change the text sprite's content later.

anyText.content = "Some new content";

Here's how the game over message text is created in the setup function.

//Add some text for the game over message
message = g.text("Game Over!", "64px Futura", "black", 20, 20);
message.x = 120;
message.y = g.canvas.height / 2 - 64;

Next, a new group is created called gameOverScene. The message text is added to it. The gameOverScene's visible property is set to false so that it's not visible when the game first starts.

//Create a `gameOverScene` group and add the message sprite to it
gameOverScene = g.group(message);

//Make the `gameOverScene` invisible for now
gameOverScene.visible = false;

At the end of the game we'll set the gameOverScene's visible property to true to display the text message. We'll also set the gameScene's visible property to false so that all the game sprites are hidden.

Keyboard interactivity

You control the player (the blue square) with the keyboard arrow keys. Ga has a built-in key object with keyboard bindings to the arrow keys and space bar. Access them like this: key.leftArray, key.rightArrow, key.upArrow, key.downArrow, key.space. All these keys have press and release methods that you can define. Here's code in the setup function that customizes the press and release methods of
Ga's pre-defined arrow keys to control the player character:

//Left arrow key `press` method
g.key.leftArrow.press = function() {
  //Change the player's velocity when the key is pressed
  player.vx = -5;
  player.vy = 0;
};

//Left arrow key `release` method
g.key.leftArrow.release = function() {
  //If the left arrow has been released, and the right arrow isn't down,
  //and the player isn't moving vertically:
  //Stop the player
  if (!g.key.rightArrow.isDown && player.vy === 0) {
    player.vx = 0;
  }
};

g.key.upArrow.press = function() {
  player.vy = -5;
  player.vx = 0;
};

g.key.upArrow.release = function() {
  if (!g.key.downArrow.isDown && player.vx === 0) {
    player.vy = 0;
  }
};

g.key.rightArrow.press = function() {
  player.vx = 5;
  player.vy = 0;
};

g.key.rightArrow.release = function() {
  if (!g.key.leftArrow.isDown && player.vy === 0) {
    player.vx = 0;
  }
};

g.key.downArrow.press = function() {
  player.vy = 5;
  player.vx = 0;
};

g.key.downArrow.release = function() {
  if (!g.key.upArrow.isDown && player.vx === 0) {
    player.vy = 0;
  }
};

You can see that the value of the player's vx and vy properties is changed depending on which keys are being pressed or released. A positive vx value will make the player move right, a negative value will make it move left. A positive vy value will make the player move down, a negative value will make it move up.

Is that too much typing? Because controlling a player character with 4 keyboard keys is such a common requirement, Ga has a built-in function called fourKeyController that accomplishes all this in one line of code.

g.fourKeyController(player, 5, 38, 39, 40, 37);

The first argument is the sprite you want to control: player. The second argument is the number of pixels that the sprite should move each frame: 5. The last four arguments are the ascii key code numbers for the top, right, bottom and left keys. (You can remember this because their order is listed clockwise, starting from the top.)

Reference to the arrow keys and space key are built-in to Ga, but you if want to use other keys, you can easily create and assign your own with Ga's keyboard method:

var customKey = g.keyboard(asciiCode);

Your new customKey has press and release methods that you can program in the same way as the examples above.

Setting the game state

The game state is the function that Ga is currently running. When Ga first starts, it runs the setup function (or whatever other function you specify in Ga's constructor function arguments.) If you want to change the game state, assign a new function to Ga's state property. Here's how:

g.state = anyFunction;

In Treasure Hunter, when the setup function is finished, the game state is set to play:

g.state = play;

This makes Ga look for and run a function called play. By default, any function assigned to the game state will run in a continuous loop, at 60 frames per second. (You can change the frame rate at any time by setting Ga's fps property). Game logic usually runs in a continuous loop, which is known as the game loop. Ga handles the loop management for you, so you don't need to worry about how it works. (In case you're curious, Ga uses a requestAnimationFrame loop with a fixed logic time step and variable rendering time. It also does sprite position interpolation to smoothe out any inconsistent spikes in the frame rate.)

If you ever need to pause the loop, just use Ga's pausemethod, like this:

g.pause();

You can start the game loop again with the resume method, like this:

g.resume();

Now let's find out how Treasure Hunter's play function works.

Game logic with the play function loop

As you've just learned, everything in the play function runs in a continuous loop.

function play() {
  //This code loops from top to bottom 60 times per second  
}

This is where all the game logic happens. It's the fun part, so let's find out what the code inside the play function does.

Moving the player sprite

Treasure Hunter uses Ga's move method inside the play function to move the sprites in the game.

g.move(player);

This is the equivalent of writing code like this:

player.x += player.vx;
player.y += player.vy;

It just updates the player's x and y position by adding its vx and vy velocity values. (Remember, those values were set by the key press and release methods.) Using move just saves you from having to type-in and look-at this very standard boilerplate code.

You can also move a whole array of sprites with one line of code by supplying the array as the argument.

g.move(arrayOfSprites);

So now you can easily move the player, but what happens when the player reaches the edges of the screen?

Containing sprites inside the screen boundaries

Use Ga's contain method to keep sprites inside the boundaries of the screen.

g.contain(player, g.stage.localBounds);

The first argument is the sprite you want to contain, and the second argument is any JavaScript object with an x, y, width, and height property. As a convenience, all Ga sprites have a property called localBounds that return an object with this information.

As you learnt earlier, stage is the root container object for all Ga's sprites, and it has the same width and height as the canvas. That means you can use its localBounds property to keep the sprite contained inside the canvas.

But you can alternatively supply a custom object to do the same thing. Here's how:

g.contain(
  player, 
  {
    x: 0,
    y: 0,
    width: 512,
    height: 512
  }
);

This will contain the player sprite to an area defined by the dimensions of the object. This is really convenient if you want to precisely fine-tune the area in which the object should be contained.

contain has an extra useful feature. If the sprite reaches one of the containment edges, contain will return a string that tells you which edge it reached: "top", "right", "bottom", or "left". Here's how you could use this feature to find out which edge of the canvas the sprite is touching:

var playerHitsEdges = g.contain(player, g.stage.localBounds);

//Display the edge of canvas that the player hit
if (playerHitsEdges) {
  message.content 
    = "The player hit the " + playerHitsEdges + " of the canvas";
}

Collision with the enemies

When the player hits any of the enemies, the width of the health bar decreases and the player becomes semi-transparent.

Treasure Hunter

How does this work?

Ga has a full suite of useful 2D geometric and tile-based collision detection methods. You can read all about them in Ga's examples folder. Treasure Hunter only uses one of these collision methods: hitTestRectangle. It takes two rectangular sprites and tells you whether they're overlapping. It will return true if they are, and false if they aren't.

g.hitTestRectangle(spriteOne, spriteTwo);

Here's how the code in the play function uses hitTestRectangle to check for a collision between any of the enemies and the player.

//Set `playerHit` to `false` before checking for a collision
var playerHit = false;

//Loop through all the sprites in the `enemies` array
enemies.forEach(function(enemy) {

  //Move the enemy
  g.move(enemy);

  //Check the enemy's screen boundaries
  var enemyHitsEdges = g.contain(enemy, g.stage.localBounds);

  //If the enemy hits the top or bottom of the stage, reverse
  //its direction
  if (enemyHitsEdges === "top" || enemyHitsEdges === "bottom") {
    enemy.vy *= -1;
  }

  //Test for a collision. If any of the enemies are touching
  //the player, set `playerHit` to `true`
  if(g.hitTestRectangle(player, enemy)) {
    playerHit = true;
  }
});

//If the player is hit...
if(playerHit) {

  //Make the player semi-transparent
  player.alpha = 0.5;

  //Reduce the width of the health bar's inner rectangle by 1 pixel
  healthBar.inner.width -= 1;

} else {

  //Make the player fully opaque (non-transparent) if it hasn't been hit
  player.alpha = 1;
}

This bit of code creates a variable called playerHit, which is initialized to false just before the forEach loop checks all the enemies for a collision.

var playerHit = false;

(Because the play function runs 60 times per second, playerHit will be reinitialized to false on every new frame.)

If hitTestRectangle returns true, the forEach loop sets playerHit to true.

if(g.hitTestRectangle(player, enemy)) {
  playerHit = true;
}

If the player has been hit, the code makes the player semi-transparent by setting its alpha value to 0.5. It also reduces the width of the healthBar's inner sprite by 1 pixel.

if(playerHit) {

  //Make the player semi-transparent
  player.alpha = 0.5;

  //Reduce the width of the health bar's inner rectangle by 1 pixel
  healthBar.inner.width -= 1;

} else {

  //Make the player fully opaque (non-transparent) if it hasn't been hit
  player.alpha = 1;
}

You can set the alpha property of sprites to any value between 0 (fully transparent) to 1 (fully opaque). A value of 0.5 makes it semi-transparent.b (Alpha is a well-worn graphic design term that just means transparency.)

This bit of code also uses the move method to move the enemies, and contain to keep them contained inside the canvas. The code also uses the return value of contain to find out if the enemy is hitting the top or bottom of the canvas. If it hits the top or bottom, the enemy's direction is reversed with the help of this code:

//Check the enemy's screen boundaries
var enemyHitsEdges = g.contain(enemy, g.stage.localBounds);

//If the enemy hits the top or bottom of the stage, reverse
//its direction
if (enemyHitsEdges === "top" || enemyHitsEdges === "bottom") {
  enemy.vy *= -1;
}

Multiplying the enemy's vy (vertical velocity) value by negative 1 makes it go in the opposite direction. It's a really simple bounce effect.

Collision with the treasure

If the player touches the treasure (the yellow square), the chimes sound plays. The player can then carry the treasure to the exit. The treasure is centered over the player and moves along with it.

Treasure Hunter

Here's the code from the play function that achieves these effects.

//Check for a collision between the player and the treasure
if (g.hitTestRectangle(player, treasure)) {

  //If the treasure is touching the player, center it over the player
  treasure.x = player.x + 8;
  treasure.y = player.y + 8;

  if(!treasure.pickedUp) {

    //If the treasure hasn't already been picked up,
    //play the `chimes` sound
    chimes.play();
    treasure.pickedUp = true;
  };
}

You can see that the code uses hitTestRectangle inside an if statement to test for a collision between the player and the treasure.

if (g.hitTestRectangle(player, treasure)) {

If it's true, the treasure is centered over the player.

treasure.x = player.x + 8;
treasure.y = player.y + 8;

If treasure.pickedUp is false, then you know that the treasure hasn't already been picked up, and you can play the chimes sound:

chimes.play();

In addition to play Ga's sound objects also have a few more methods that you can use to control them: pause, restart and playFrom. (Use playFrom to start playing the sound from a specific second in the sound file, like this: soundObject.playFrom(5). This will make the sound start playing from the 5 second mark.)

You can also set the sound object's volume by assigning a value between 0 and 1. Here's how to set the volume to mid-level (50%).

soundObject.volume = 0.5;

You can set the sound object's pan by assigning a value between -1 (left speaker) to 1 (right speaker). A pan value of 0 makes the sound equal volume in both speakers. Here's how you could set the pan to be slightly more prominent in the left speaker.

soundObject.pan = -0.2;

If you want to make a sound repeat continuously, set its loop property to true.

soundObject.loop = true;

Ga uses a lightweight wrapper for the WebAudio API to achieve all these effects.

Because you don't want to play the chimes sound more than once after the treasure has been picked up, the code sets treasure.pickedUp to true just after the sound plays.

treasure.pickedUp = true;

Now that the player has picked up the treasure, how can you check for the end of the game?

Ending the game

There are two ways the game can end. The player's health can run out, in which case the game is lost. Or, the player can successfully carry the treasure to the exit, in which case the game is won. If either of these two conditions are met, the game's state is set to end and the message text's content displays the outcome. Here's the last bit of code in the play function that does this:

//Does the player have enough health? If the width of the `innerBar`
//is less than zero, end the game and display "You lost!"
if (healthBar.inner.width < 0) {
  g.state = end;
  message.content = "You lost!";
}

//If the player has brought the treasure to the exit,
//end the game and display "You won!"
if (g.hitTestRectangle(treasure, exit)) {
  g.state = end;
  message.content = "You won!";
}

The end function is really simple. It just hides the gameScene and displays the gameOverScene.

function end() {
  gameScene.visible = false;
  gameOverScene.visible = true;
}

And that's it for Treasure Hunter! Before you continue, try making your own game from scratch using some of these same techniques. When you're ready, read on!

Using images

There are three main ways you can use images in your Ga games.

Use individual image files for each sprite.
Use a texture atlas. This is a single image file that includes sub-images for each sprite in your game. The image file is accompanied by a matching JSON data file that describes the name, size and location of each sub-image.
Use a tileset (also known as a spritesheet). This is also a single image file that includes sub-images for each sprite. However, unlike a texture atlas, it doesn't come with a JSON file describing the sprite data. Instead, you need to specify the size and location of each sprite in your game code with JavaScript. This can have some advantages over a texture atlas in certain circumstances.

All three ways of making image sprites use Ga's sprite method. Here's the simplest way of using it to make an image sprite.

var imageSprite = g.sprite("images/theSpriteImage.png");

In this next section we'll update Treasure Hunter with image sprites, and you'll learn all three ways of adding images to your games.

(All the images in this section were created by Lanea Zimmerman. You can find more of her artwork here. Thanks, Lanea!)

Individual images

Open and play the next version of Treasure Hunter: 02_treasureHunterImages.html (you'll find it in the tutorials folder.) It plays exactly the same as the first version, but all the colored squares have been replaced by images.

(Click the image and follow the link to play the game.) Take a look at the source code, and you'll notice that the game logic and structure is exactly the same as the first version of the game. The only thing that's changed is the appearance of the sprites. How was this done?

Loading image files

Each sprite in the game uses an individual PNG image file. You'll find all the images in the tutorials' images sub-folder.

Treasure Hunter

Before you can use them to make sprites, you need to pre-load them into Ga's assets. The easiest way to do this is to list the image names, with their full file paths, in Ga's assets array when you first initialize the engine.

var g = ga(
  512, 512, setup,
  [
    "images/explorer.png",
    "images/dungeon.png",
    "images/blob.png",
    "images/treasure.png",
    "images/door.png",
    "sounds/chimes.wav"
  ]
);
g.start();

(If you open up the JavaScript console in the web browser, you can monitor the loading progress of these assets.)

Now you can access any of these images in your game code like this:

g.image("images/blob.png")

This is just a short-cut for accessing the image directly in the assets object like this:

g.assets["images/blob.png"]

You can use whichever style you prefer. In any case, the image file is just an ordinary JavaScript Image object, so you can use it the same way you would any other Image object.

Although pre-loading the images and other assets is the simplest way to get them into your game, you can also load assets at any other time using the assets object's load method. Just supply an array of strings that list the asset names and their file paths.

g.assets.load([
  "images/imageOne.png", 
  "images/imageTwo.png",
  "sounds/chimes.wav"
]);

Next, assign a callback function called whenLoaded that will run when the assets have loaded.

g.assets.whenLoaded = function() {
  //Do something when the assets have loaded
};

Now that you've loaded the images into the game, let's find out how to use them to make sprites.

Making sprites with images

Create an image sprite using the sprite method using the same format you learnt earlier. Here's how to create a sprite using the dungeon.png image. (dungeon.png is a 512 by 512 pixel background image.)

dungeon = g.sprite("images/dungeon.png");

That's all! Now instead of displaying as a simple colored rectangle, the sprite will be displayed as a 512 by 512 image. There's no need to specify the width or height, because Ga figures that our for you automatically based on the size of the image. You can use all the other sprite properties, like x, y, width, and height, just as you would with ordinary rectangle sprites.

Here's the code from the setup function that creates the dungeon background, exit door, player and treasure, and adds them all to the gameScene group.

//The dungeon background
dungeon = g.sprite("images/dungeon.png");

//The exit door
exit = g.sprite("images/door.png");
exit.x = 32;

//The player sprite
player = g.sprite("images/explorer.png");
player.x = 68;
player.y = g.canvas.height / 2 - player.halfWidth;

//Create the treasure
treasure = g.sprite("images/treasure.png");

//Position it next to the left edge of the canvas
treasure.x = g.canvas.width - treasure.width - 32;
treasure.y = g.canvas.height / 2 - treasure.halfHeight;

//Create a `pickedUp` property on the treasure to help us Figure
//out whether or not the treasure has been picked up by the player
treasure.pickedUp = false;

//Create the `gameScene` group and add all the sprites
gameScene = g.group(dungeon, exit, player, treasure);

(As a slightly more efficient improvement to the original version of this code, group creates the gameScene and groups the sprites in a single step.)

Look familiar? That's right, the only code that has changed are the lines that create the sprites. This modularity is a feature of Ga that lets you create quick game prototypes using simple shapes that you can easily swap out for detailed images as your game ideas develops. The rest of the code in the game can remain as-is.

Fine-tuning the containment area

One small improvement that was made to this new version Treasure Hunter is the new way that the sprites are contained inside the walls of the dungeon. They're contained in such a way that naturally matches the 2.5D perspective of the artwork, as shown by the green square in this screen shot:

Treasure Hunter

This is a very easy modification to make. All you need to do is supply the contain method with a custom object that defines the size and position of the containing rectangle. Here's how:

g.contain(
  player,
  {
    x: 32, y: 16,
    width: g.canvas.width - 32,
    height: g.canvas.height - 32
  }
);

Just tweak the x, y, width and height values so that the containing area looks natural for the game you're making.

Using a texture atlas

If you’re working on a big, complex game, you’ll want a fast and efficient way to work with images. A texture atlas can help you do this. A texture atlas is actually two separate files that are closely related:

A single PNG tileset image file that contains all the images you want to use in your game. (A tileset image is sometimes called a spritesheet.)
A JSON file that describes the size and position of those sub-images in the tileset.

Using a texture atlas is a big time saver. You can arrange the tileset’s sub-images in any order and the JSON file will keep track of their sizes and positions for you. This is really convenient because it means the sizes and positions of the sub-images aren’t hard-coded into your game program. If you make changes to the tileset, like adding images, resizing them, or removing them, just re-publish the JSON file and your game will use that updated data to display the images correctly. If you’re going to be making anything bigger than a very small game, you’ll definitely want to use a texture atlas.

The de-facto standard for tileset JSON data is the format that is output by a popular software tool called Texture Packer (Texture Packer's "Essential" license is free ). Even if you don’t use Texture Packer, similar tools like Shoebox output JSON files in the same format. Let’s find out how to use it to make a texture atlas with Texture Packer, and how to load it into a game.

Preparing the images

You first need individual PNG images for each image in your game. You've already got them for Treasure Hunter, so you're all set. Open Texture Packer and choose the {JS} configuration option. Drag your game images into its workspace. You can also point Texture Packer to any folder that contains your images. Texture Packer will automatically arrange the images on a single tileset image, and give them names that match their original image file names. It will give them a 2 pixel padding by default.

Texture Packer

Each of the sub-images in the atlas is called a frame. Although it's just one big image, the texture atlas has 5 frames. The name of each frame is the same its original PNG file name: "dungeon.png", "blob.png", "explorer.png", "treasure.png" and "door.png". These frames names are used to help the atlas reference each sub-image.

When you’re done, make sure the Data Format is set to JSON (Hash) and click the Publish button. Choose the file name and location, and save the published files. You’ll end up with a PNG file and a JSON file. In this example my file names are treasureHunter.json and treasureHunter.png. To make your life easier, just keep both files in your project’s images folder. (Think of the JSON file as extra metadata for the image file.)

loading the texture atlas

To load the texture atlas into your game, just include the JSON file in Ga's assets array when you initialize the game.

var g = ga(
  512, 512, setup,
  [
    "images/treasureHunter.json",
    "sounds/chimes.wav"
  ]
);
g.start();

That's all! You don't have to load the PNG file - Ga does that automatically in the background. The JSON file is all you need to tell Ga which tileset frame (sub-image) to display.

Now if you want to use a frame from the texture atlas to make a sprite, you can do it like this:

anySprite = g.sprite("frameName.png");

Ga will create the sprite and display the correct image from the texture atlas's tileset.

Here's how to you could create the sprites in Treasure Hunter using texture atlas frames:

//The dungeon background image
dungeon = g.sprite("dungeon.png");

//The exit door
exit = g.sprite("door.png");
exit.x = 32;

//The player sprite
player = g.sprite("explorer.png");
player.x = 68;
player.y = g.canvas.height / 2 - player.halfWidth;

//The treasure
treasure = g.sprite("treasure.png");

That's all! Ga knows that those are texture atlas frame names, not individual images, and it displays them directly from the tileset.

If you ever need to access the texture atlas's JSON file in your game, you can get it like this:

jsonFile = g.json("jsonFileName.json");

Take a look at treasureHunterAtlas.html file in the tutorials folder to see a working example of how to load a texture atlas and use it to make sprites.

Alien Armada

The next example game in this series of tutorials is Alien Armada. Can you destroy 60 aliens before one of them lands and destroys the Earth? Click the image link below to play the game:

Use the arrow keys to move and press the space bar to shoot. The aliens descend from the top of the screen with increasing frequency as the game progresses. Here's how the game is played:

![Alien Armada gameplay](/tutoria

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Readme

Goal

Getting Started

Examples

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Ga

Table of contents:

Features

The plugins

Coming soon...

Ga's philosophy and technical constraints

Minifying, crushing and compressing

Contributions and Licencing

Hexi

Tutorials

Treasure Hunter

Setting up the HTML container page

Initializing the Ga engine

Define your "global" variables

Initialize your game with a setup function

Customizing the canvas

Creating the chimes sound object

Creating game scenes

Making sprites

Positioning sprites

Assigning dynamic properties

Creating the enemy sprites

The health bar

The game over scene

Keyboard interactivity

Setting the game state

Game logic with the play function loop

Moving the player sprite

Containing sprites inside the screen boundaries

Collision with the enemies

Collision with the treasure

Ending the game

Using images

Individual images

Loading image files

Making sprites with images

Fine-tuning the containment area

Using a texture atlas

Preparing the images

loading the texture atlas

Alien Armada

Creating the `chimes` sound object