HTML5 Game Development – Lesson 8
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Join For FreeThis is our next game development article. We continue a series of
articles on game development in HTML5 using canvas. Today I will show
you how to apply some physics to your project (with using Box2D). Box2D is
popular open source engine that simulates 2D physics for applications.
2D Physics Engine is a hot topic in game development. With the help of
this physics engine, we can easily create a playable game by just defining an
environment and a simple rule.
Here you can read our previous lesson: Developing Your First HTML5 Game – Lesson 7.
Live Demo
Live Demo
download in package
Here you can read our previous lesson: Developing Your First HTML5 Game – Lesson 7.
Here are our demo and downloadable packages:
Live Demo
download in package
Ok, download the example files and let's start coding !
Step 0. Pre-phase
First, you have to download the Box2D library here.
Step 1. HTML
Today we have to link all necessary library files to our project.
index.html
<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="utf-8" />
<title>HTML5 Game Development - Lesson 8 | Script Tutorials</title>
<link href="css/main.css" rel="stylesheet" type="text/css" />
<script src="js/protoclass.js"></script>
<script src="js/jquery-1.6.min.js"></script>
<!-- box2djs -->
<script src="js/box2d/common/b2Settings.js"></script>
<script src="js/box2d/common/math/b2Vec2.js"></script>
<script src="js/box2d/common/math/b2Mat22.js"></script>
<script src="js/box2d/common/math/b2Math.js"></script>
<script src="js/box2d/collision/b2AABB.js"></script>
<script src="js/box2d/collision/b2Bound.js"></script>
<script src="js/box2d/collision/b2BoundValues.js"></script>
<script src="js/box2d/collision/b2Pair.js"></script>
<script src="js/box2d/collision/b2PairCallback.js"></script>
<script src="js/box2d/collision/b2BufferedPair.js"></script>
<script src="js/box2d/collision/b2PairManager.js"></script>
<script src="js/box2d/collision/b2BroadPhase.js"></script>
<script src="js/box2d/collision/b2Collision.js"></script>
<script src="js/box2d/collision/Features.js"></script>
<script src="js/box2d/collision/b2ContactID.js"></script>
<script src="js/box2d/collision/b2ContactPoint.js"></script>
<script src="js/box2d/collision/b2Distance.js"></script>
<script src="js/box2d/collision/b2Manifold.js"></script>
<script src="js/box2d/collision/b2OBB.js"></script>
<script src="js/box2d/collision/b2Proxy.js"></script>
<script src="js/box2d/collision/ClipVertex.js"></script>
<script src="js/box2d/collision/shapes/b2Shape.js"></script>
<script src="js/box2d/collision/shapes/b2ShapeDef.js"></script>
<script src="js/box2d/collision/shapes/b2BoxDef.js"></script>
<script src="js/box2d/collision/shapes/b2CircleDef.js"></script>
<script src="js/box2d/collision/shapes/b2CircleShape.js"></script>
<script src="js/box2d/collision/shapes/b2MassData.js"></script>
<script src="js/box2d/collision/shapes/b2PolyDef.js"></script>
<script src="js/box2d/collision/shapes/b2PolyShape.js"></script>
<script src="js/box2d/dynamics/b2Body.js"></script>
<script src="js/box2d/dynamics/b2BodyDef.js"></script>
<script src="js/box2d/dynamics/b2CollisionFilter.js"></script>
<script src="js/box2d/dynamics/b2Island.js"></script>
<script src="js/box2d/dynamics/b2TimeStep.js"></script>
<script src="js/box2d/dynamics/contacts/b2ContactNode.js"></script>
<script src="js/box2d/dynamics/contacts/b2Contact.js"></script>
<script src="js/box2d/dynamics/contacts/b2ContactConstraint.js"></script>
<script src="js/box2d/dynamics/contacts/b2ContactConstraintPoint.js"></script>
<script src="js/box2d/dynamics/contacts/b2ContactRegister.js"></script>
<script src="js/box2d/dynamics/contacts/b2ContactSolver.js"></script>
<script src="js/box2d/dynamics/contacts/b2CircleContact.js"></script>
<script src="js/box2d/dynamics/contacts/b2Conservative.js"></script>
<script src="js/box2d/dynamics/contacts/b2NullContact.js"></script>
<script src="js/box2d/dynamics/contacts/b2PolyAndCircleContact.js"></script>
<script src="js/box2d/dynamics/contacts/b2PolyContact.js"></script>
<script src="js/box2d/dynamics/b2ContactManager.js"></script>
<script src="js/box2d/dynamics/b2World.js"></script>
<script src="js/box2d/dynamics/b2WorldListener.js"></script>
<script src="js/box2d/dynamics/joints/b2JointNode.js"></script>
<script src="js/box2d/dynamics/joints/b2Joint.js"></script>
<script src="js/box2d/dynamics/joints/b2JointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2DistanceJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2DistanceJointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2Jacobian.js"></script>
<script src="js/box2d/dynamics/joints/b2GearJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2GearJointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2MouseJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2MouseJointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2PrismaticJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2PrismaticJointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2PulleyJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2PulleyJointDef.js"></script>
<script src="js/box2d/dynamics/joints/b2RevoluteJoint.js"></script>
<script src="js/box2d/dynamics/joints/b2RevoluteJointDef.js"></script>
<script src="js/script.js"></script>
</head>
<body>
<header>
<h2>HTML5 Game Development - Lesson 8</h2>
<a href="http://www.script-tutorials.com/html5-game-development-lesson-8/" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
</header>
<div class="container">
<canvas id="game" width="800" height="600"></canvas>
</div>
</body>
</html>
Step 2. CSS
css/main.css
I won’t publish CSS styles today; there are only a few page layout styles. You can find this file in our package.
Step 3. JS
js/jquery-1.6.min.js and js/protoclass.js
Both libraries available in our package. Next file is the most important – it is the main code of our game:
js/script.js
var canvas, ctx;
var canvasWidth;
var canvasHeight;
var world;
var iBorder = 5;
// get rand number between X and Y
function getRand(x, y) {
return Math.floor(Math.random()*y)+x;
}
$(function() {
// create the world
world = createWorld();
// get canvas and context
canvas = document.getElementById('game');
ctx = canvas.getContext('2d');
canvasWidth = parseInt(canvas.width);
canvasHeight = parseInt(canvas.height);
// create the ground
createGround(canvasWidth / 2, canvasHeight - iBorder, canvasWidth / 2, iBorder, 0);
createGround(iBorder, canvasHeight / 2, iBorder, canvasHeight / 2, 0); // left border
createGround(canvasWidth - iBorder, canvasHeight / 2, iBorder, canvasHeight / 2, 0); // right border
// add first rand object
addObjects();
// draw frame
frame();
});
// add random objects
function addObjects() {
var iVar = getRand(1, 2);
if (iVar == 1) {
var x = getRand(100, 600);
var y = 0;
var r = getRand(10, 40);
createCircleAt(x, y, r);
} else if (iVar == 2) {
var x = getRand(100, 600);
var y = 0;
var w = getRand(5, 40);
var h = getRand(5, 40);
createBoxAt(x, y, w, h);
}
// set timer
setTimeout(addObjects, 500);
}
// draw frame
function frame() {
world.Step(1.0 / 60, 1);
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
// draw world
drawWorld(world, ctx);
// set timer
setTimeout(frame, 10);
}
// create world
function createWorld() {
// set the size of the world
var worldAABB = new b2AABB();
worldAABB.minVertex.Set(-1000, -1000);
worldAABB.maxVertex.Set(1000, 1000);
// Define the gravity
var gravity = new b2Vec2(0, 200);
// set to ignore sleeping object
var doSleep = false;
// finally create the world with the size, graivty and sleep object parameter.
return new b2World(worldAABB, gravity, doSleep);
}
// create ground (box-type object)
function createGround(x, y, width, height, rotation) {
// box shape definition
var groundSd = new b2BoxDef();
groundSd.extents.Set(width, height);
groundSd.restitution = 0.4;
var groundBd = new b2BodyDef();
groundBd.AddShape(groundSd);
groundBd.position.Set(x, y);
groundBd.rotation = rotation * Math.PI / 180;
return world.CreateBody(groundBd);
}
// create box
function createBoxAt(x, y, w, h) {
var boxSd = new b2BoxDef();
boxSd.density = 1.0;
boxSd.friction = 1.0;
boxSd.restitution = .5;
boxSd.extents.Set(w, h);
// add to world as shape
var boxBd = new b2BodyDef();
boxBd.AddShape(boxSd);
boxBd.position.Set(x,y);
return world.CreateBody(boxBd);
}
// create circle
function createCircleAt(x, y, r) {
var boxSd = new b2CircleDef();
boxSd.density = 1.0;
boxSd.friction = 1.0;
boxSd.restitution = .5;
boxSd.radius = r;
// add to world as shape
var boxBd = new b2BodyDef();
boxBd.AddShape(boxSd);
boxBd.position.Set(x,y);
return world.CreateBody(boxBd);
}
// draw world
function drawWorld(world, context) {
for (var b = world.m_bodyList; b != null; b = b.m_next) {
for (var s = b.GetShapeList(); s != null; s = s.GetNext()) {
drawShape(s, context);
}
}
}
// draw shapes
function drawShape(shape, context) {
context.strokeStyle = '#0000ff';
context.fillStyle = 'rgba(100, 100, 255, 0.8)';
context.beginPath();
switch (shape.m_type) {
case b2Shape.e_circleShape:
var circle = shape;
var pos = circle.m_position;
var r = circle.m_radius;
var segments = 16.0;
var theta = 0.0;
var dtheta = 2.0 * Math.PI / segments;
context.moveTo(pos.x + r, pos.y);
for (var i = 0; i < segments; i++) {
var d = new b2Vec2(r * Math.cos(theta), r * Math.sin(theta));
var v = b2Math.AddVV(pos, d);
context.lineTo(v.x, v.y);
theta += dtheta;
}
context.lineTo(pos.x + r, pos.y);
context.moveTo(pos.x, pos.y);
var ax = circle.m_R.col1;
var pos2 = new b2Vec2(pos.x + r * ax.x, pos.y + r * ax.y);
context.lineTo(pos2.x, pos2.y);
break;
case b2Shape.e_polyShape:
var poly = shape;
var tV = b2Math.AddVV(poly.m_position, b2Math.b2MulMV(poly.m_R, poly.m_vertices[0]));
context.moveTo(tV.x, tV.y);
for (var i = 0; i < poly.m_vertexCount; i++) {
var v = b2Math.AddVV(poly.m_position, b2Math.b2MulMV(poly.m_R, poly.m_vertices[i]));
context.lineTo(v.x, v.y);
}
context.lineTo(tV.x, tV.y);
break;
}
context.fill();
context.stroke();
}
I have added my comments everywhere. Hope that all this code is pretty understandable.
Live Demo
download in package
Conclusion
And that’s it! You have just completed our new lesson with HTML5 and Box2D. Congratulations!
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Published at DZone with permission of Andrey Prikaznov, DZone MVB. See the original article here.
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