HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.
In CodePen, whatever you write in the HTML editor is what goes within the <body>
tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html>
tag. If you want to add classes there that can affect the whole document, this is the place to do it.
In CodePen, whatever you write in the HTML editor is what goes within the <body>
tags in a basic HTML5 template. If you need things in the <head>
of the document, put that code here.
The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.
CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.
It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.
To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit-
or -moz-
.
We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).
Any URLs added here will be added as <link>
s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.
You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.
You can also link to another Pen here (use the .css
URL Extension) and we'll pull the CSS from that Pen and include it. If it's using a matching preprocessor, use the appropriate URL Extension and we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.
JavaScript preprocessors can help make authoring JavaScript easier and more convenient.
Babel includes JSX processing.
Any URL's added here will be added as <script>
s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.
You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.
If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.
You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.
Search for and use JavaScript packages from npm here. By selecting a package, an import
statement will be added to the top of the JavaScript editor for this package.
Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.
All packages are different, so refer to their docs for how they work.
If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.
If active, Pens will autosave every 30 seconds after being saved once.
If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.
If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.
Visit your global Editor Settings.
<!--
@2014 Jeff Ibacache | http://dev.everblind.me/
License: https://github.com/everblind/js-playground/blob/master/license.md
Source: https://github.com/everblind/js-playground/tree/master/canvas-asteroids
-->
<div id="info">
<h1>Canvas Asteroids:</h1>
<p>Use [A][S][W][D] or [←][↑][↓][→] to MOVE</p>
<p>Use [SPACE] or [K] to SHOOT</p>
</div>
<canvas id="canvas"></canvas>
* {
margin: 0;
}
canvas {
position: absolute;
width: 100%;
height: 100%;
background: #262626;
}
#info {
color: #FFF;
font-family: "Lucida Sans Typewriter", "Lucida Console", Monaco, "Bitstream Vera Sans Mono", monospace;
margin: 10px 10px 0;
padding: 8px;
background: #161616;
position: absolute;
z-index: 1;
}
#info h1 {
font-size: 18px;
}
#info p {
font-size: 11px;
}
//pool.js ...........................................................
var Pool = (function()
{
//exposed methods:
var create = function(type, size)
{
var obj = Object.create(def);
obj.init(type, size);
return obj;
};
//Ship definition:
var def =
{
_type: null,
_size: null,
_pointer: null,
_elements:null,
init: function(type, size)
{
this._type = type;
this._size = size;
this._pointer = size;
this._elements = [];
var i = 0;
var length = this._size;
for(i; i < length; ++i)
{
this._elements[i] = this._type.create();
}
},
getElement: function()
{
if(this._pointer > 0) return this._elements[--this._pointer];
return null;
},
disposeElement: function(obj)
{
this._elements[this._pointer++] = obj;
}
};
return {create:create};
}());
//vec2d.js ...........................................................
var Vec2D = (function()
{
//exposed methods:
var create = function(x, y)
{
var obj = Object.create(def);
obj.setXY(x, y);
return obj;
};
//Vec2D definition:
var def =
{
_x: 1,
_y: 0,
getX: function()
{
return this._x;
},
setX: function(value)
{
this._x = value;
},
getY: function()
{
return this._y;
},
setY: function(value)
{
this._y = value;
},
setXY: function(x, y)
{
this._x = x;
this._y = y;
},
getLength: function()
{
return Math.sqrt(this._x * this._x + this._y * this._y);
},
setLength: function(length)
{
var angle = this.getAngle();
this._x = Math.cos(angle) * length;
this._y = Math.sin(angle) * length;
},
getAngle: function()
{
return Math.atan2(this._y, this._x);
},
setAngle: function(angle)
{
var length = this.getLength();
this._x = Math.cos(angle) * length;
this._y = Math.sin(angle) * length;
},
add: function(vector)
{
this._x += vector.getX();
this._y += vector.getY();
},
sub: function(vector)
{
this._x -= vector.getX();
this._y -= vector.getY();
},
mul: function(value)
{
this._x *= value;
this._y *= value;
},
div: function(value)
{
this._x /= value;
this._y /= value;
}
};
return {create:create};
}());
//particle.js ...........................................................
var Particle = (function()
{
//exposed methods:
var create = function()
{
var obj = Object.create(def);
obj.radius = 2;
obj.color = '#FFF';
obj.lifeSpan = 0;
obj.fric = 0.98;
obj.pos = Vec2D.create(0, 0);
obj.vel = Vec2D.create(0, 0);
obj.blacklisted = false;
return obj;
};
//Ship definition:
var def =
{
radius: null,
color: null,
lifeSpan: null,
fric: null,
pos: null,
vel: null,
blacklisted: null,
update: function()
{
this.pos.add(this.vel);
this.vel.mul(this.fric);
this.radius -= 0.1;
if(this.radius < 0.1) this.radius = 0.1;
if(this.lifeSpan-- < 0)
{
this.blacklisted = true;
}
},
reset: function()
{
this.blacklisted = false;
}
};
return {create:create};
}());
//bullet.js ...........................................................
var Bullet = (function()
{
//exposed methods:
var create = function()
{
var obj = Object.create(def);
obj.radius = 4;
obj.color = '#FFF';
obj.pos = Vec2D.create(0, 0);
obj.vel = Vec2D.create(0, 0);
obj.blacklisted = false;
return obj;
};
//Bullet definition:
var def =
{
radius: null,
color: null,
pos: null,
vel: null,
blacklisted: null,
update: function()
{
this.pos.add(this.vel);
},
reset: function()
{
this.blacklisted = false;
}
};
return {create:create};
}());
//asteroid.js ...........................................................
var Asteroid = (function()
{
//exposed methods:
var create = function()
{
var obj = Object.create(def);
obj.radius = 40;
obj.color = '#FF5900';
obj.pos = Vec2D.create(0, 0);
obj.vel = Vec2D.create(0, 0);
obj.blacklisted = false;
obj.type = 'b';
obj.sides = (Math.random() * 2 + 7) >> 0;
obj.angle = 0;
obj.angleVel = (1 - Math.random() * 2) * 0.01;
return obj;
};
//Ship definition:
var def =
{
radius: null,
color: null,
pos: null,
vel: null,
blacklisted: null,
type: null,
sides: null,
angle: null,
angleVel: null,
update: function()
{
this.pos.add(this.vel);
this.angle += this.angleVel;
},
reset: function()
{
this.blacklisted = false;
}
};
return {create:create};
}());
//ship.js ...........................................................
var Ship = (function()
{
//exposed methods:
var create = function(x, y, ref)
{
var obj = Object.create(def);
obj.ref = ref;
obj.angle = 0;
obj.pos = Vec2D.create(x, y);
obj.vel = Vec2D.create(0, 0);
obj.thrust = Vec2D.create(0, 0);
obj.idle = false;
obj.radius = 8;
obj.idleDelay = 0;
return obj;
};
//Ship definition:
var def =
{
angle: null,
pos: null,
vel: null,
thrust: null,
ref: null,
bulletDelay: null,
idle: null,
radius: null,
update: function()
{
this.vel.add(this.thrust);
this.pos.add(this.vel);
if(this.vel.getLength() > 5) this.vel.setLength(5);
++this.bulletDelay;
if(this.idle)
{
if(++this.idleDelay > 120)
{
this.idleDelay = 0;
this.idle = false;
this.ref.resetGame();
}
}
},
shoot: function()
{
if(this.bulletDelay > 8)
{
this.ref.generateShot();
this.bulletDelay = 0;
}
}
};
return {create:create};
}());
//canvas-asteroids.js ...........................................................
//common vars
var canvas;
var context;
var screenWidth;
var screenHeight;
var doublePI = Math.PI * 2;
//game vars
var ship;
var particlePool;
var particles;
var bulletPool;
var bullets;
var asteroidPool;
var asteroids;
var hScan;
var asteroidVelFactor = 0;
//keyboard vars
var keyLeft = false;
var keyUp = false;
var keyRight = false;
var keyDown = false;
var keySpace = false;
window.getAnimationFrame =
window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function(callback)
{
window.setTimeout(callback, 16.6);
};
window.onload = function()
{
canvas = document.getElementById('canvas');
context = canvas.getContext('2d');
window.onresize();
keyboardInit();
particleInit();
bulletInit();
asteroidInit();
shipInit();
loop();
};
window.onresize = function()
{
if(!canvas) return;
screenWidth = canvas.clientWidth;
screenHeight = canvas.clientHeight;
canvas.width = screenWidth;
canvas.height = screenHeight;
hScan = (screenHeight / 4) >> 0;
};
function keyboardInit()
{
window.onkeydown = function(e)
{
switch(e.keyCode)
{
//key A or LEFT
case 65:
case 37:
keyLeft = true;
break;
//key W or UP
case 87:
case 38:
keyUp = true;
break;
//key D or RIGHT
case 68:
case 39:
keyRight = true;
break;
//key S or DOWN
case 83:
case 40:
keyDown = true;
break;
//key Space
case 32:
case 75:
keySpace = true;
break;
}
e.preventDefault();
};
window.onkeyup = function(e)
{
switch(e.keyCode)
{
//key A or LEFT
case 65:
case 37:
keyLeft = false;
break;
//key W or UP
case 87:
case 38:
keyUp = false;
break;
//key D or RIGHT
case 68:
case 39:
keyRight = false;
break;
//key S or DOWN
case 83:
case 40:
keyDown = false;
break;
//key Space
case 75:
case 32:
keySpace = false;
break;
}
e.preventDefault();
};
}
function particleInit()
{
particlePool = Pool.create(Particle, 100);
particles = [];
}
function bulletInit()
{
bulletPool = Pool.create(Bullet, 40);
bullets = [];
}
function asteroidInit()
{
asteroidPool = Pool.create(Asteroid, 30);
asteroids = [];
}
function shipInit()
{
ship = Ship.create(screenWidth >> 1, screenHeight >> 1, this);
}
function loop()
{
updateShip();
updateParticles();
updateBullets();
updateAsteroids();
checkCollisions();
render();
getAnimationFrame(loop);
}
function updateShip()
{
ship.update();
if(ship.idle) return;
if(keySpace) ship.shoot();
if(keyLeft) ship.angle -= 0.1;
if(keyRight) ship.angle += 0.1;
if(keyUp)
{
ship.thrust.setLength(0.1);
ship.thrust.setAngle(ship.angle);
generateThrustParticle();
}
else
{
ship.vel.mul(0.94);
ship.thrust.setLength(0);
}
if(ship.pos.getX() > screenWidth) ship.pos.setX(0);
else if(ship.pos.getX() < 0) ship.pos.setX(screenWidth);
if(ship.pos.getY() > screenHeight) ship.pos.setY(0);
else if(ship.pos.getY() < 0) ship.pos.setY(screenHeight);
}
function generateThrustParticle()
{
var p = particlePool.getElement();
//if the particle pool doesn't have more elements, will return 'null'.
if(!p) return;
p.radius = Math.random() * 3 + 2;
p.color = '#FFF';
p.lifeSpan = 80;
p.pos.setXY(ship.pos.getX() + Math.cos(ship.angle) * -14, ship.pos.getY() + Math.sin(ship.angle) * -14);
p.vel.setLength(8 / p.radius);
p.vel.setAngle(ship.angle + (1 - Math.random() * 2) * (Math.PI / 18));
p.vel.mul(-1);
//particles[particles.length] = p; same as: particles.push(p);
particles[particles.length] = p;
}
function updateParticles()
{
var i = particles.length - 1;
for(i; i > -1; --i)
{
var p = particles[i];
if(p.blacklisted)
{
p.reset();
particles.splice(particles.indexOf(p), 1);
particlePool.disposeElement(p);
continue;
}
p.update();
}
}
function updateBullets()
{
var i = bullets.length - 1;
for(i; i > -1; --i)
{
var b = bullets[i];
if(b.blacklisted)
{
b.reset();
bullets.splice(bullets.indexOf(b), 1);
bulletPool.disposeElement(b);
continue;
}
b.update();
if(b.pos.getX() > screenWidth) b.blacklisted = true;
else if(b.pos.getX() < 0) b.blacklisted = true;
if(b.pos.getY() > screenHeight) b.blacklisted = true;
else if(b.pos.getY() < 0) b.blacklisted = true;
}
}
function updateAsteroids()
{
var i = asteroids.length - 1;
for(i; i > -1; --i)
{
var a = asteroids[i];
if(a.blacklisted)
{
a.reset();
asteroids.splice(asteroids.indexOf(a), 1);
asteroidPool.disposeElement(a);
continue;
}
a.update();
if(a.pos.getX() > screenWidth + a.radius) a.pos.setX(-a.radius);
else if(a.pos.getX() < -a.radius) a.pos.setX(screenWidth + a.radius);
if(a.pos.getY() > screenHeight + a.radius) a.pos.setY(-a.radius);
else if(a.pos.getY() < -a.radius) a.pos.setY(screenHeight + a.radius);
}
if(asteroids.length < 5)
{
var factor = (Math.random() * 2) >> 0;
generateAsteroid(screenWidth * factor, screenHeight * factor, 60 , 'b');
}
}
function generateAsteroid(x, y, radius, type)
{
var a = asteroidPool.getElement();
//if the bullet pool doesn't have more elements, will return 'null'.
if(!a) return;
a.radius = radius;
a.type = type;
a.pos.setXY(x, y);
a.vel.setLength(1 + asteroidVelFactor);
a.vel.setAngle(Math.random() * (Math.PI * 2));
//bullets[bullets.length] = b; same as: bullets.push(b);
asteroids[asteroids.length] = a;
asteroidVelFactor += 0.025;
}
function checkCollisions()
{
checkBulletAsteroidCollisions();
checkShipAsteroidCollisions();
}
function checkBulletAsteroidCollisions()
{
var i = bullets.length - 1;
var j;
for(i; i > -1; --i)
{
j = asteroids.length - 1;
for(j; j > -1; --j)
{
var b = bullets[i];
var a = asteroids[j];
if(checkDistanceCollision(b, a))
{
b.blacklisted = true;
destroyAsteroid(a);
}
}
}
}
function checkShipAsteroidCollisions()
{
var i = asteroids.length - 1;
for(i; i > -1; --i)
{
var a = asteroids[i];
var s = ship;
if(checkDistanceCollision(a, s))
{
if(s.idle) return;
s.idle = true;
generateShipExplosion();
destroyAsteroid(a);
}
}
}
function generateShipExplosion()
{
var i = 18;
for(i; i > -1; --i)
{
var p = particlePool.getElement();
//if the particle pool doesn't have more elements, will return 'null'.
if(!p) return;
p.radius = Math.random() * 6 + 2;
p.lifeSpan = 80;
p.color = '#FFF';
p.vel.setLength(20 / p.radius);
p.vel.setAngle(ship.angle + (1 - Math.random() * 2) * doublePI);
p.pos.setXY(ship.pos.getX() + Math.cos(p.vel.getAngle()) * (ship.radius * 0.8), ship.pos.getY() + Math.sin(p.vel.getAngle()) * (ship.radius * 0.8));
//particles[particles.length] = p; same as: particles.push(p);
particles[particles.length] = p;
}
}
function checkDistanceCollision(obj1, obj2)
{
var vx = obj1.pos.getX() - obj2.pos.getX();
var vy = obj1.pos.getY() - obj2.pos.getY();
var vec = Vec2D.create(vx, vy);
if(vec.getLength() < obj1.radius + obj2.radius)
{
return true;
}
return false;
}
function destroyAsteroid(asteroid)
{
asteroid.blacklisted = true;
generateAsteroidExplosion(asteroid);
resolveAsteroidType(asteroid);
}
function generateAsteroidExplosion(asteroid)
{
var i = 18;
for(i; i > -1; --i)
{
var p = particlePool.getElement();
//if the particle pool doesn't have more elements, will return 'null'.
if(!p) return;
p.radius = Math.random() * (asteroid.radius >> 2) + 2;
p.lifeSpan = 80;
p.color = '#FF5900';
p.vel.setLength(20 / p.radius);
p.vel.setAngle(ship.angle + (1 - Math.random() * 2) * doublePI);
p.pos.setXY(asteroid.pos.getX() + Math.cos(p.vel.getAngle()) * (asteroid.radius * 0.8), asteroid.pos.getY() + Math.sin(p.vel.getAngle()) * (asteroid.radius * 0.8));
//particles[particles.length] = p; same as: particles.push(p);
particles[particles.length] = p;
}
}
function resolveAsteroidType(asteroid)
{
switch(asteroid.type)
{
case 'b':
generateAsteroid(asteroid.pos.getX(), asteroid.pos.getY(), 40, 'm');
generateAsteroid(asteroid.pos.getX(), asteroid.pos.getY(), 40, 'm');
break;
case 'm':
generateAsteroid(asteroid.pos.getX(), asteroid.pos.getY(), 20, 's');
generateAsteroid(asteroid.pos.getX(), asteroid.pos.getY(), 20, 's');
break;
}
}
function render()
{
context.fillStyle = '#262626';
context.globalAlpha = 0.4;
context.fillRect(0, 0, screenWidth, screenHeight);
context.globalAlpha = 1;
renderShip();
renderParticles();
renderBullets();
renderAsteroids();
renderScanlines();
}
function renderShip()
{
if(ship.idle) return;
context.save();
context.translate(ship.pos.getX() >> 0, ship.pos.getY() >> 0);
context.rotate(ship.angle);
context.strokeStyle = '#FFF';
context.lineWidth = (Math.random() > 0.9) ? 2 : 1;
context.beginPath();
context.moveTo(10, 0);
context.lineTo(-10, -10);
context.lineTo(-10, 10);
context.lineTo(10, 0);
context.stroke();
context.closePath();
context.restore();
}
function renderParticles()
{
//inverse for loop = more performance.
var i = particles.length - 1;
for(i; i > -1; --i)
{
var p = particles[i];
context.beginPath();
context.strokeStyle = p.color;
context.arc(p.pos.getX() >> 0, p.pos.getY() >> 0, p.radius, 0, doublePI);
if(Math.random() > 0.4) context.stroke();
context.closePath();
}
}
function renderBullets()
{
//inverse for loop = more performance.
var i = bullets.length - 1;
for(i; i > -1; --i)
{
var b = bullets[i];
context.beginPath();
context.strokeStyle = b.color;
context.arc(b.pos.getX() >> 0, b.pos.getY() >> 0, b.radius, 0, doublePI);
if(Math.random() > 0.2) context.stroke();
context.closePath();
}
}
function renderAsteroids()
{
//inverse for loop = more performance.
var i = asteroids.length - 1;
for(i; i > -1; --i)
{
var a = asteroids[i];
context.beginPath();
context.lineWidth = (Math.random() > 0.2) ? 4 : 3;
context.strokeStyle = a.color;
var j = a.sides;
context.moveTo((a.pos.getX() + Math.cos(doublePI * (j / a.sides) + a.angle) * a.radius) >> 0, (a.pos.getY() + Math.sin(doublePI * (j / a.sides) + a.angle) * a.radius) >> 0);
for(j; j > -1; --j)
{
context.lineTo((a.pos.getX() + Math.cos(doublePI * (j / a.sides) + a.angle) * a.radius) >> 0, (a.pos.getY() + Math.sin(doublePI * (j / a.sides) + a.angle) * a.radius) >> 0);
}
if(Math.random() > 0.2) context.stroke();
context.closePath();
}
}
function renderScanlines()
{
//inverse for loop = more performance.
var i = hScan;
context.globalAlpha = 0.05;
context.lineWidth = 1;
for(i; i > -1; --i)
{
context.beginPath();
context.moveTo(0, i * 4);
context.lineTo(screenWidth, i * 4);
context.strokeStyle = (Math.random() > 0.0001) ? '#FFF' : '#222';
context.stroke();
}
context.globalAlpha = 1;
}
function generateShot()
{
var b = bulletPool.getElement();
//if the bullet pool doesn't have more elements, will return 'null'.
if(!b) return;
b.radius = 1;
b.pos.setXY(ship.pos.getX() + Math.cos(ship.angle) * 14, ship.pos.getY() + Math.sin(ship.angle) * 14);
b.vel.setLength(10);
b.vel.setAngle(ship.angle);
//bullets[bullets.length] = b; same as: bullets.push(b);
bullets[bullets.length] = b;
}
function resetGame()
{
asteroidVelFactor = 0;
ship.pos.setXY(screenWidth >> 1, screenHeight >> 1);
ship.vel.setXY(0, 0);
resetAsteroids();
}
function resetAsteroids()
{
var i = asteroids.length - 1;
for(i; i > -1; --i)
{
var a = asteroids[i];
a.blacklisted = true;
}
}
Also see: Tab Triggers