HTML5 Game Development – Lesson 9
Today we continue the series of articles on game development in HTML5
using canvas. For today I have prepared new game. I have updated our
lesson 4 and added fireballs, enemies and collision detection. So, now
our dragon can cast fireballs and kill enemies (plus, we have scores
now). Now this game is much more interactive.
Our previous article you can read here: Developing Your First HTML5 Game – Lesson 8.
download in package
download in package
Published at DZone with permission of Andrey Prikaznov, author and DZone MVB. (source)Our previous article you can read here: Developing Your First HTML5 Game – Lesson 8.
Here are our demo and downloadable package:
Live Demodownload in package
Ok, download the example files and let's start coding !
Step 1. HTML
First – our basic html code:
<!DOCTYPE html>
<html lang="en" >
<head>
<meta charset="utf-8" />
<title>HTML5 Game Development - Lesson 9 | Script Tutorials</title>
<link href="css/main.css" rel="stylesheet" type="text/css" />
<!--[if lt IE 9]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<script src="js/jquery.js"></script>
<script src="js/script.js"></script>
</head>
<body>
<header tabindex="0">
<h2>HTML5 Game Development - Lesson 9</h2>
<a href="http://www.script-tutorials.com/html5-game-development-lesson-9/" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
</header>
<div class="container">
<canvas id="scene" width="1000" height="600" tabindex="1"></canvas>
</div>
</body>
</html>Step 2. CSS
Here are the CSS styles.
css/main.cssI won’t publish styles today – it is just page layout styles, nothing interesting. Always available in package.
Step 3. JS
js/script.js// inner variables
var canvas, ctx;
var backgroundImage;
var iBgShiftX = 100;
var dragon, enemy = null; // game objects
var balls = [];
var enemies = [];
var dragonW = 75; // dragon width
var dragonH = 70; // dragon height
var iSprPos = 0; // initial sprite frame
var iSprDir = 0; // initial dragon direction
var iEnemyW = 128; // enemy width
var iEnemyH = 128; // enemy height
var iBallSpeed = 10; // initial ball speed
var iEnemySpeed = 2; // initial enemy speed
var dragonSound; // dragon sound
var wingsSound; // wings sound
var explodeSound, explodeSound2; // explode sounds
var laughtSound; // wings sound
var bMouseDown = false; // mouse down state
var iLastMouseX = 0;
var iLastMouseY = 0;
var iScore = 0;
// -------------------------------------------------------------
// objects :
function Dragon(x, y, w, h, image) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.image = image;
this.bDrag = false;
}
function Ball(x, y, w, h, speed, image) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.speed = speed;
this.image = image;
}
function Enemy(x, y, w, h, speed, image) {
this.x = x;
this.y = y;
this.w = w;
this.h = h;
this.speed = speed;
this.image = image;
}
// -------------------------------------------------------------
// get random number between X and Y
function getRand(x, y) {
return Math.floor(Math.random()*y)+x;
}
// draw functions :
function drawScene() { // main drawScene function
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); // clear canvas
// draw background
iBgShiftX += 4;
if (iBgShiftX >= 1045) {
iBgShiftX = 0;
}
ctx.drawImage(backgroundImage, 0 + iBgShiftX, 0, 1000, 940, 0, 0, 1000, 600);
// update sprite positions
iSprPos++;
if (iSprPos >= 9) {
iSprPos = 0;
}
// in case of mouse down - move dragon more close to our mouse
if (bMouseDown) {
if (iLastMouseX > dragon.x) {
dragon.x += 5;
}
if (iLastMouseY > dragon.y) {
dragon.y += 5;
}
if (iLastMouseX < dragon.x) {
dragon.x -= 5;
}
if (iLastMouseY < dragon.y) {
dragon.y -= 5;
}
}
// draw dragon
ctx.drawImage(dragon.image, iSprPos*dragon.w, iSprDir*dragon.h, dragon.w, dragon.h, dragon.x - dragon.w/2, dragon.y - dragon.h/2, dragon.w, dragon.h);
// draw fireballs
if (balls.length > 0) {
for (var key in balls) {
if (balls[key] != undefined) {
ctx.drawImage(balls[key].image, balls[key].x, balls[key].y);
balls[key].x += balls[key].speed;
if (balls[key].x > canvas.width) {
delete balls[key];
}
}
}
}
// draw enemies
if (enemies.length > 0) {
for (var ekey in enemies) {
if (enemies[ekey] != undefined) {
ctx.drawImage(enemies[ekey].image, enemies[ekey].x, enemies[ekey].y);
enemies[ekey].x += enemies[ekey].speed;
if (enemies[ekey].x < - iEnemyW) {
delete enemies[ekey];
// play laught sound
laughtSound.currentTime = 0;
laughtSound.play();
}
}
}
}
// collision detection
if (balls.length > 0) {
for (var key in balls) {
if (balls[key] != undefined) {
if (enemies.length > 0) {
for (var ekey in enemies) {
if (enemies[ekey] != undefined && balls[key] != undefined) {
if (balls[key].x + balls[key].w > enemies[ekey].x && balls[key].y + balls[key].h > enemies[ekey].y && balls[key].y < enemies[ekey].y + enemies[ekey].h) {
delete enemies[ekey];
delete balls[key];
iScore++;
// play explode sound #2
explodeSound2.currentTime = 0;
explodeSound2.play();
}
}
}
}
}
}
}
// draw score
ctx.font = '16px Verdana';
ctx.fillStyle = '#fff';
ctx.fillText('Score: ' + iScore * 10, 900, 580);
ctx.fillText('Plese click "1" to cast fireball', 100, 580);
}
// -------------------------------------------------------------
// initialization
$(function(){
canvas = document.getElementById('scene');
ctx = canvas.getContext('2d');
var width = canvas.width;
var height = canvas.height;
// load background image
backgroundImage = new Image();
backgroundImage.src="images/hell.jpg";
backgroundImage.onload = function() {
}
backgroundImage.onerror = function() {
console.log('Error loading the background image.');
}
// 'Dragon' music init
dragonSound = new Audio('media/dragon.wav');
dragonSound.volume = 0.9;
// 'Laught' music init
laughtSound = new Audio('media/laught.wav');
laughtSound.volume = 0.9;
// 'Explode' music inits
explodeSound = new Audio('media/explode1.wav');
explodeSound.volume = 0.9;
explodeSound2 = new Audio('media/explosion.wav');
explodeSound2.volume = 0.9;
// 'Wings' music init
wingsSound = new Audio('media/wings.wav');
wingsSound.volume = 0.9;
wingsSound.addEventListener('ended', function() { // loop wings sound
this.currentTime = 0;
this.play();
}, false);
wingsSound.play();
// initialization of empty ball
var oBallImage = new Image();
oBallImage.src="images/fireball.png";
oBallImage.onload = function() { }
// initialization of empty enemy
var oEnemyImage = new Image();
oEnemyImage.src="images/enemy.png";
oEnemyImage.onload = function() { }
// initialization of dragon
var oDragonImage = new Image();
oDragonImage.src="images/dragon.gif";
oDragonImage.onload = function() {
dragon = new Dragon(400, 300, dragonW, dragonH, oDragonImage);
}
$('#scene').mousedown(function(e) { // binding mousedown event (for dragging)
var mouseX = e.layerX || 0;
var mouseY = e.layerY || 0;
if(e.originalEvent.layerX) { // changes for jquery 1.7
mouseX = e.originalEvent.layerX;
mouseY = e.originalEvent.layerY;
}
bMouseDown = true;
if (mouseX > dragon.x- dragon.w/2 && mouseX < dragon.x- dragon.w/2 +dragon.w &&
mouseY > dragon.y- dragon.h/2 && mouseY < dragon.y-dragon.h/2 +dragon.h) {
dragon.bDrag = true;
dragon.x = mouseX;
dragon.y = mouseY;
}
});
$('#scene').mousemove(function(e) { // binding mousemove event
var mouseX = e.layerX || 0;
var mouseY = e.layerY || 0;
if(e.originalEvent.layerX) {
mouseX = e.originalEvent.layerX;
mouseY = e.originalEvent.layerY;
}
// saving last coordinates
iLastMouseX = mouseX;
iLastMouseY = mouseY;
// perform dragon dragging
if (dragon.bDrag) {
dragon.x = mouseX;
dragon.y = mouseY;
}
// change direction of dragon (depends on mouse position)
if (mouseX > dragon.x && Math.abs(mouseY-dragon.y) < dragon.w/2) {
iSprDir = 0;
} else if (mouseX < dragon.x && Math.abs(mouseY-dragon.y) < dragon.w/2) {
iSprDir = 4;
} else if (mouseY > dragon.y && Math.abs(mouseX-dragon.x) < dragon.h/2) {
iSprDir = 2;
} else if (mouseY < dragon.y && Math.abs(mouseX-dragon.x) < dragon.h/2) {
iSprDir = 6;
} else if (mouseY < dragon.y && mouseX < dragon.x) {
iSprDir = 5;
} else if (mouseY < dragon.y && mouseX > dragon.x) {
iSprDir = 7;
} else if (mouseY > dragon.y && mouseX < dragon.x) {
iSprDir = 3;
} else if (mouseY > dragon.y && mouseX > dragon.x) {
iSprDir = 1;
}
});
$('#scene').mouseup(function(e) { // binding mouseup event
dragon.bDrag = false;
bMouseDown = false;
// play dragon sound
dragonSound.currentTime = 0;
dragonSound.play();
});
$(window).keydown(function(event){ // keyboard alerts
switch (event.keyCode) {
case 49: // '1' key
balls.push(new Ball(dragon.x, dragon.y, 32, 32, iBallSpeed, oBallImage));
// play explode sound #1
explodeSound.currentTime = 0;
explodeSound.play();
break;
}
});
setInterval(drawScene, 30); // loop drawScene
// generate enemies randomly
var enTimer = null;
function addEnemy() {
clearInterval(enTimer);
var randY = getRand(0, canvas.height - iEnemyH);
enemies.push(new Enemy(canvas.width, randY, iEnemyW, iEnemyH, - iEnemySpeed, oEnemyImage));
var interval = getRand(5000, 10000);
enTimer = setInterval(addEnemy, interval); // loop drawScene
}
addEnemy();
});In the beginning I added two new objects: Ball (or fireball) and Enemy. Each object has own attributes set (like position, size, image, speed). After, I added drawing balls and enemies for our ‘drawScene’ function. Plus, at the bottom of this function you can see the collision detection method:
// collision detection
if (balls.length > 0) {
for (var key in balls) {
if (balls[key] != undefined) {
if (enemies.length > 0) {
for (var ekey in enemies) {
if (enemies[ekey] != undefined && balls[key] != undefined) {
if (balls[key].x + balls[key].w > enemies[ekey].x && balls[key].y + balls[key].h > enemies[ekey].y && balls[key].y < enemies[ekey].y + enemies[ekey].h) {
delete enemies[ekey];
delete balls[key];
iScore++;
// play explode sound #2
explodeSound2.currentTime = 0;
explodeSound2.play();
}
}
}
}
}
}
}And finally, we have to add our enemies periodically (randomly):
// generate enemies randomly
var enTimer = null;
function addEnemy() {
clearInterval(enTimer);
var randY = getRand(0, canvas.height - iEnemyH);
enemies.push(new Enemy(canvas.width, randY, iEnemyW, iEnemyH, - iEnemySpeed, oEnemyImage));
var interval = getRand(5000, 10000);
enTimer = setInterval(addEnemy, interval); // loop drawScene
}
addEnemy();Step 4. Custom files
images/dragon.gif, images/enemy.png, images/fireball.png, images/hell.jpgmedia/dragon.wav, media/explode1.wav, media/explosion.wav, media/laught.wav, media/wings.wavAll these files available in our package.
Live Demodownload in package
Conclusion
Do you like our new updated game? 
I will be glad to see your thanks and comments. Good luck!
(Note: Opinions expressed in this article and its replies are the opinions of their respective authors and not those of DZone, Inc.)
