chem

chem

canvas-based game engine and toolchain optimized for rapid development.

Features

• Automatically creates a spritesheet for your assets and then loads the assets at runtime.
• Provides convenient API for drawing animated sprites in a canvas
  • Supports anchor points and rotation
• Write code in JavaScript or other compile-to-javascript languages such as Coffee-Script.
• Uses browserify to compile your code which allows you to harness the power of code on npm.
  • For example, A* search
  • Allows you to organize code modules using require and module.exports syntax.
• Everything from code to spritesheet is compiled automatically when you save.
• Handles main loop and frame skipping.
• Convenient API for keyboard and mouse input.

Usage

# install dependencies in ubuntu
sudo apt-get install libcairo2-dev

# start with a nearly-empty project,
# such as a freshly created project from github with only a .git/ and README.md.
cd my-project

# init the project with chem-cli
npm install chem-cli
./node_modules/.bin/chem init

# the `dev` command will run a development server which will automatically recompile your code,
# generate your spritesheets, and serve your assets.
# after running `init` above, simply:
npm run dev

# see more commands
./node_modules/.bin/chem

See chem-cli for more information.

Synopsis

Layout

Source files

./chemfile.js
./src/main.js
./public/index.html
./assets/img/ship.png
./assets/img/explosion/01.png
...
./assets/img/explosion/12.png

Generated files

./public/main.js
./public/spritesheet.png
./public/animations.json

./src/main.js

var chem = require('chem');
var Vec2d = chem.vec2d;

chem.onReady(function () {
    var canvas = document.getElementById("game");
    var engine = new chem.Engine(canvas);
    var batch = new chem.Batch();
    var boom = new chem.Sound('sfx/boom.ogg');
    var ship = new chem.Sprite('ship', {
        batch: batch,
        pos: new Vec2d(200, 200),
        rotation: Math.PI / 2
    });
    var shipVel = new Vec2d();
    var rotationSpeed = Math.PI * 0.04;
    var thrustAmt = 0.1;
    engine.on('update', function (dt, dx) {
        ship.pos.add(shipVel);

        // rotate the ship with left and right arrow keys
        if (engine.buttonState(chem.button.KeyLeft)) {
            ship.rotation -= rotationSpeed * dx;
        }
        if (engine.buttonState(chem.button.KeyRight)) {
            ship.rotation += rotationSpeed * dx;
        }

        // apply forward and backward thrust with up and down arrow keys
        var thrust = new Vec2d(Math.cos(ship.rotation), Math.sin(ship.rotation));
        if (engine.buttonState(chem.button.KeyUp)) {
            shipVel.add(thrust.scaled(thrustAmt * dx));
        }
        if (engine.buttonState(chem.button.KeyDown)) {
            shipVel.sub(thrust.scaled(thrustAmt * dx));
        }

        // press space to blow yourself up
        if (engine.buttonJustPressed(chem.button.KeySpace)) {
            boom.play();
            ship.setAnimationName('boom');
            ship.setFrameIndex(0);
            ship.on('animationend', function() {
                ship.delete();
            });
        }
    });
    engine.on('draw', function (context) {
        // clear canvas to black
        context.fillStyle = '#000000'
        context.fillRect(0, 0, engine.size.x, engine.size.y);

        // draw all sprites in batch
        engine.draw(batch);

        // draw a little fps counter in the corner
        context.fillStyle = '#ffffff'
        engine.drawFps();
    });
    engine.start();
    canvas.focus();
});

./chemfile.js

// the main source file which depends on the rest of your source files.
exports.main = 'src/main';

exports.spritesheet = {
  // you can override any of these in individual animation declarations
  defaults: {
    delay: 0.05,
    loop: false,
    // possible values: a Vec2d instance, or one of:
    // ["center", "topleft", "topright", "bottomleft", "bottomright",
    //  "top", "right", "bottom", "left"]
    anchor: "center"
  },
  animations: {
    boom: {
      // frames can be a list of filenames or a string to match the beginning
      // of files with. If you leave it out entirely, it defaults to the
      // animation name.
      frames: "explosion"
    },
    ship: {}
  }
};

./public/index.html

<!doctype html>
<html>
  <head>
    <title>Chem Example</title>
  </head>
  <body style="text-align: center">
    <canvas id="game" width="853" height="480"></canvas>
    <p>Use the arrow keys to move around and space to destroy yourself.</p>
    <script type="text/javascript" src="main.js"></script>
  </body>
</html>

See the demo in action.

Demo Projects Using Chem

• Meteor Attack - dodge meteors in space
• Disinfecticide - use extreme measures to control a deadly disease outbreak.
• holocaust - rebuild society after a nuclear holocaust ravages the world
• Dr. Chemical's Lab - PyWeek #14 entry, ported to chem
• vapor - vaporware game. Not cool yet.

Documentation

Developing With Chem

Chemfile

Start by looking at your chemfile. This file contains all the instructions on how to build your game.

This file, like every other source file in your game, can be in any compile- to-JavaScript language (including JavaScript itself) that you choose.

• main - this is the entry point into your game. Chem will use browserify with this as the input file. Often this is set to src/main.js.

• spritesheet

  • defaults - for each animation, these are the default values that will be used if you do not specify one.
  • animations - these will be available when you create a sprite.
    • anchor - the "center of gravity" point. pos is centered here, and a sprite's rotation rotates around this point. Use a Vec2d instance for this value.
    • frames - frames can be a list of filenames or a string to match the beginning of files with. if you leave it out entirely, it defaults to the animation name.
    • delay - number of seconds between frames.
    • loop - whether an animation should start over when it ends. You can override this in individual sprites.

Use any "compile to JS" language

Supported languages:

• JavaScript (obviously)
• Coffee-Script
• LiveScript
• Coco

Getting Started

The first step is to require "chem":

var chem = require('chem');

chem.onReady(function() {
    // Now you can go for it. All asssets are loaded.
});

Vec2d Convention

As a convention, any Vec2d instances you get from Chem are not clones. That is, pay careful attention not to perform destructive behavior on the Vec2d instances returned from the API.

Not Using a Spritesheet

If you omit the spritesheet object in your chemfile, no spritesheet files will be generated. Be sure to set chem.useSpritesheet = false in your app code to avoiding attempting to load the missing resources.

Reference

Batch

var Batch = require('chem').Batch;

A Batch is a set of sprites which you can conveniently draw using the Engine::draw(batch) method.

Batch::add(sprite):

Adds a sprite to the batch. If called multiple times for the same sprite,
the sprite is only added once.

Batch::remove(sprite):

Removes a sprite from the batch. OK to call multiple times.

button

var button = require('chem').button;

Enumeration to get the button that a person is activating. Keyboard buttons start with Key and mouse buttons start with Mouse.

For example, the left mouse button is chem.button.MouseLeft and the right arrow key is chem.button.KeyRight.

See also:

• Engine::buttonState
• Engine::buttonJustPressed
• Engine::buttonJustReleased
• Engine:: 'buttondown' event (button)
• Engine:: 'buttonup' event (button)

See lib/button.js for the full listing.

Engine

var Engine = require('chem').Engine;

methods

Engine::new(canvas)

Create an instance of the engine and bind it to a canvas:

var engine = new chem.Engine(document.getElementById("the-canvas"));

Engine::setSize(size)

Resize the game.

Engine::start()

Call this to start the main loop and start listening to events.

Engine::setMinFps(minFps)

If the FPS drops below this value, your engine will lag instead of trying
to compensate with a larger dt/dx sent to `update`
Defaults to 20.

See also `Engine:: 'update' event(dt, dx)`

Engine::stop()

Call this to stop the main loop and stop listening to events.

Engine::buttonState(button)

Check if `button` is currently pressed. See also `button`.

Engine::buttonJustPressed(button)

Call from the `update` event. It returns `true` for the 1 frame
after the button was pressed.

See also `button`.

Engine::buttonJustReleased(button)

Call from the `update` event. It returns `true` for the 1 frame
after the button was released.

See also `button`.

Engine::draw(batch)

Call from the `draw` event and pass in the `Batch` that you want to draw.
All of the sprites will be drawn with the correct rotations, offsets,
scaling, `zOrder`, and animation applied.

Engine::drawFps()

Draws the current frames per second in the corner of your game with
whatever fillColor and font are currently set.

properties

Engine::size

Read only. `Vec2d` instance. Use `Engine::setSize` if you want to update
the size.

Engine::fps

Read only. Contains an up to date value for the current frames per second.

Engine::canvas

Read only. The canvas element that the engine is using.

Engine::mousePos

Read only. `Vec2d` instance representing the current mouse position
relative to the canvas.

Engine::buttonCaptureExceptions

Read/write. This is an object which is initially empty and contains
buttons which the game should bubble up instead of capturing.

Example:

```js
// now you can press Ctrl+R, etc
engine.buttonCaptureExceptions[chem.button.KeyCtrl] = true;
```

events

These are events that you can subscribe to. See EventEmitter on how to subscribe to events.

Engine:: 'update' event (dt, dx)

Fired as often as possible, capping at about 60 FPS. Use it to compute
the next frame in your game.

`dt` is the "delta time" - the amount of time in seconds that has passed 
since `update` was last fired.

`dx` is a multiplier intended to adjust your physics. If your game is
running perfectly smoothly at 60 FPS, `dx` will be exactly 1. If your game
is running half as fast as it should, at 30 FPS, `dx` will be 2. `dx` is
equal to `dt` * 60.

Engine:: 'draw' event (context)

You should perform all canvas drawing based on your game state in response
to this event.

See also:
 * `Engine::draw`

Engine:: 'mousemove' event (pos, button)

Fired when the mouse moves.
`pos`: a `Vec2d` instance.
`button`: an enum from `button`.

See also:
 * `Engine::mousePos`

Engine:: 'buttondown' event (button) Engine:: 'buttonup' event (button)

Fired when the player presses a button down or up, respectively.
`button`: an enum from `button`.

Sound

var Sound = require('chem').Sound;

new Sound(url)

Example:

var sound = new chem.Sound('url/to/sound.ogg');

sound.play()

Plays the sound. If the sound is already playing, it will play another
instance at the same time.

Returns the HTML5 Audio object that is generating the sound, which has these
methods: `pause()`, `play()`

And these properties: `currentTime`, `duration`

sound.setVolume(value)

Sets the `volume` property. Same as HTML5 Audio object.

sound.setPreload(value)

Sets the `preload` property. Same as HTML5 Audio object.

Sprite

var Sprite = require('chem').Sprite;

methods

Sprite::new(animationName, params)

Example:

var sprite = new chem.Sprite('some_animation_name', {
  pos: new Vec2d(0, 0),
  scale: new Vec2d(1, 1),
  zOrder: 0,
  batch: some_batch,
  rotation: 0,
  visible: true,
  frameIndex: 0,
  loop: true
});

All the params are optional.

Sprite::setAnimationName(animationName)

Changes the sprite's animation to the one indexed by `animationName`.

Note that you probably also want to call `setFrameIndex(0)` if you want
the new animation to start from the beginning.

Sprite::setAnimation(animation)

Changes the sprite's animation to `animation`.

Note that you probably also want to call `setFrameIndex(0)` if you want
the new animation to start from the beginning.

Sprite::getSize()

Like `Sprite::size` but takes scale and current frame into account.

Sprite::getAnchor()

Convenience method to get a `Vec2d` representing the anchor position.
Takes into account scale.
Does not take into account rotation.

Sprite::getTopLeft() Sprite::getBottomRight()

Convenience methods returning a `Vec2d` instance of corners of the sprite.
Takes into account scale and current frame.
Does not take into account rotation.

Sprite::getTop() Sprite::getLeft() Sprite::getBottom() Sprite::getRight()

Convenience methods returning the location of edges of the sprite.
Takes into account scale and current frame.
Does not take into account rotation.

Sprite::setLeft(x) Sprite::setRight(x) Sprite::setTop(y) Sprite::setBottom(y)

Convenience methods to set the location of edges of the sprite.
Takes into account scale and current frame.
Does not take into account rotation.

Sprite::isTouching(sprite)

Returns boolean of whether the sprite is colliding with another.
Takes into account scale and current frame.
Does not take into account rotation.

Sprite::hitTest(vec2d)

Returns boolean of whether the point is inside the bounding box
of the sprite.
Takes into account scale and current frame.
Does not take into account rotation.

Sprite::setVisible(visible)

Hides the sprite but keeps it ready to display again.
See also `Sprite::delete()`.

Sprite::setZOrder(zOrder)

Use to layer sprites the way you want to. Start with 0 as the bottom layer.
When you want to put something on top, use 1 for the zOrder, 2 for
something on top of that, and so on.
See also `Sprite::zOrder`

Sprite::setFrameIndex(frameIndex)

Set the frame to show when the sprite is rendered. Animation will continue
from this frame as usual. To find out the frame count, use
`sprite.animation.frames.length`.

Sprite::setLoop(loop)

This value overrides the animation's loop property. If set to `null`,
it will fall back to the animation's loop property.
See also `Sprite::loop`.

Sprite::setAnimationStartDate(animationStartDate)

Does the same thing as `Sprite::setFrameIndex(frameIndex)` except you
specify a date instead of a frame index.

Sprite::getFrameIndex()

Returns the index of the current frame. See also
`Sprite::setFrameIndex(frameIndex)`

Sprite::delete()

Indicates that the sprite should release all resources and no longer
display on the canvas.
See also `Sprite::setVisible(visible)`.

properties

Sprite::pos

`Vec2d`. Get or set the position in the canvas this sprite is drawn.

Sprite::size

Read only. `Vec2d` width and height of the first frame, not taking into
account `scale` or current frame.

Sprite::scale

`Vec2d`. Get or set the scale with which the sprite is drawn.

Sprite::zOrder

Read only. Use `Sprite::setZOrder` to change the `zOrder` of a sprite.

Sprite::batch

Read only. Use `Batch::add(sprite)` and `Batch::remove(sprite)` to
change this value.

Sprite::rotation

Get or set the angle of the sprite, in radians. Going over 2 * pi is OK.

Sprite::loop

Read only. Use `Sprite::setLoop(loop)` to set this value.

Sprite::id

Read only. Uniquely identifies this `Sprite` among others.

Sprite::animation

Read only. The current animation of the sprite. Properties of `animation`
are:

 * `anchor` - `Vec2d` instance
 * `delay` - seconds
 * `loop` - boolean
 * `frames` - `[{size, pos}]` - both `size` and `pos` here are `Vec2d`s.

Sprite::animationName

Read only.

events

These are events that you can subscribe to. See EventEmitter on how to subscribe to events.

Sprite:: 'animationend' event

Fired when the animation completes. If `loop` is true, this will be at a
regular interval. If `loop` is false, this will fire only once, until you
reset the frame index.

See also:
 * `Sprite::setFrameIndex(frameIndex)`

vec2d

var vec2d = require('chem').vec2d;

See node-vec2d

Developing chem

See also chem-cli

# set up dev environment for chem itself:
sudo apt-get install libcairo2-dev
sudo npm link

History

0.4.5

• sound: ability to set preload and volume properties
• focus canvas on mouse down - fixes focus problem

0.4.4

• add Sprite::hitTest(vec2d)
• fix not respecting loop property in chemfile

0.4.3

• proper bubbling of events for mouse events. (fixes hiding the cursor when mouse down if you have canvas.style.cursor = 'none')

0.4.2

• support buttonJustReleased
• ability to add button capture exceptions

0.4.1

• chem.getImage moved to chem.resources.getImage
• chem.animations moved to chem.resources.animations
• chem.spritesheet moved to chem.resources.spritesheet
• fix double bootstrap bug

0.4.0

• use browserify for packaging instead of jspackage
• snake_case api changed to camelCase
• chem.Button changed to chem.button
• chem.Vec2d changed to chem.vec2d
• "animation_end" changed to "animationend"

0.3.0

• rewrite chem to be faster and less error prone
• support node.js v0.10

0.2.7

• update jspackage - fixes dependencies rendered out of order sometimes

0.2.6

• add sprite.alpha property

0.2.5

• add div and divBy to Vec2d

0.2.4

• correctly expose animations and spritesheet

0.2.3

(recalled)

0.2.2

• expose animations, spritesheet, and getImage
• throw error objects, not strings

0.2.1

• add top, bottom, left, right anchor shortcuts
• Vec2d: add ceil and ceiled
• drawFps: text align left