HTML5 Game Development – Navigating Your Spaceship- Lesson 3

Oct 19, 2011

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HTML5 Game Development – Lesson 3

Today we continue a series of articles on game development in HTML5 using canvas. Finally, today we will start adding animation, and few more interesting features. Our demonstration will include a spaceship flying through space, and a new element – the Dialogue. The dialogue will contain two pages, and our button will toggle the dialog pages + hide the dialog on the second click.

Our previous article you can read here: Developing Your First HTML5 Game – Lesson 2. Our base script will taken from previous letter.

Here are our demo and downloadable package:

Live Demo

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download in package

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Ok, download the example files and lets start coding !

Step 1. HTML

Here are all html of my demo

index.html

<!DOCTYPE html>
<html lang="en" >
    <head>
        <meta charset="utf-8" />
        <title>HTML5 Game Development - Lesson 3 | 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 type="text/javascript" src="js/jquery-1.5.2.min.js"></script>
        <script type="text/javascript" src="js/script.js"></script>
    </head>
    <body>
        <div class="container">
            <canvas id="scene" width="800" height="600"></canvas>
        </div>
        <footer>
            <h2>HTML5 Game Development - Lesson 3</h2>
            <a href="https://script-tutorials.com/html5-game-development-navigating-your-spaceship-lesson-3" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
        </footer>
    </body>
</html>

Step 2. CSS

Here are used CSS styles.

css/main.css

/* general styles */
*{
    margin:0;
    padding:0;
}
@font-face {
    font-family: "DS-Digital";
    src: url("../fonts/Ds-digib.ttf");
}
body {
    background-color:#bababa;
    background-image: -webkit-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
    background-image: -moz-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
    background-image: -o-radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
    background-image: radial-gradient(600px 300px, circle, #ffffff, #bababa 60%);
    color:#fff;
    font:14px/1.3 Arial,sans-serif;
    min-height:1000px;
}
.container {
    width:100%;
}
.container > * {
    display:block;
    margin:50px auto;
}
footer {
    background-color:#212121;
    bottom:0;
    box-shadow: 0 -1px 2px #111111;
    display:block;
    height:70px;
    left:0;
    position:fixed;
    width:100%;
    z-index:100;
}
footer h2{
    font-size:22px;
    font-weight:normal;
    left:50%;
    margin-left:-400px;
    padding:22px 0;
    position:absolute;
    width:540px;
}
footer a.stuts,a.stuts:visited{
    border:none;
    text-decoration:none;
    color:#fcfcfc;
    font-size:14px;
    left:50%;
    line-height:31px;
    margin:23px 0 0 110px;
    position:absolute;
    top:0;
}
footer .stuts span {
    font-size:22px;
    font-weight:bold;
    margin-left:5px;
}
h3 {
    text-align:center;
}
#scene {
    position:relative;
}

Pay attention to ‘@font-face’. We will using this way to link custom font file (ttf) to our lesson (to draw at canvas).

Step 3. JS

js/jquery-1.5.2.min.js

We will using jQuery for our demo. This allows easy bind different events (for mouse etc). Next file most important (here are all our html5 functional):

js/script.js

// inner variables
var canvas, ctx;
var button;
var backgroundImage;
var spaceShip;
var iBgShiftX = 1024;
var bDrawDialog = true;
var iDialogPage = 1;
// -------------------------------------------------------------
// objects :
function Button(x, y, w, h, state, image) {
    this.x = x;
    this.y = y;
    this.w = w;
    this.h = h;
    this.state = state;
    this.imageShift = 0;
    this.image = image;
}
function SpaceShip(x, y, w, h, image) {
    this.x = x;
    this.y = y;
    this.w = w;
    this.h = h;
    this.image = image;
    this.bDrag = false;
}
// -------------------------------------------------------------
// draw functions :
function clear() { // clear canvas function
    ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}
function drawDialog() { // draw dialog function
    if (bDrawDialog) {
        var bg_gradient = ctx.createLinearGradient(0, 200, 0, 400);
        bg_gradient.addColorStop(0.0, 'rgba(160, 160, 160, 0.8)');
        bg_gradient.addColorStop(1.0, 'rgba(250, 250, 250, 0.8)');
        ctx.beginPath(); // custom shape begin
        ctx.fillStyle = bg_gradient;
        ctx.moveTo(100, 100);
        ctx.lineTo(700, 100);
        ctx.lineTo(700, 500);
        ctx.lineTo(100, 500);
        ctx.lineTo(100, 100);
        ctx.closePath(); // custom shape end
        ctx.fill(); // fill custom shape
        ctx.lineWidth = 2;
        ctx.strokeStyle = 'rgba(128, 128, 128, 0.5)';
        ctx.stroke(); // draw border
        // draw the title text
        ctx.font = '42px DS-Digital';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'top';
        ctx.shadowColor = '#000';
        ctx.shadowOffsetX = 2;
        ctx.shadowOffsetY = 2;
        ctx.shadowBlur = 2;
        ctx.fillStyle = '#fff';
        if (iDialogPage == 1) {
            ctx.fillText('Welcome to lesson #3', ctx.canvas.width/2, 150);
            ctx.font = '24px DS-Digital';
            ctx.fillText('After closing dialog you will able', ctx.canvas.width/2, 250);
            ctx.fillText('to handle with spaceship with your mouse', ctx.canvas.width/2, 280);
        } else if (iDialogPage == 2) {
            ctx.fillText('Second page of dialog', ctx.canvas.width/2, 150);
            ctx.font = '24px DS-Digital';
            ctx.fillText('Any another text', ctx.canvas.width/2, 250);
        }
    }
}
function drawScene() { // main drawScene function
    clear(); // clear canvas
    // draw background
    iBgShiftX -= 10;
    if (iBgShiftX <= 0) {
        iBgShiftX = 1024;
    }
    ctx.drawImage(backgroundImage, 0 + iBgShiftX, 0, 1024, 768, 0, 0, 800, 600);
    // draw space ship
    ctx.drawImage(spaceShip.image, 0, 0, spaceShip.w, spaceShip.h, spaceShip.x-128, spaceShip.y-128, spaceShip.w, spaceShip.h);
    // draw dialog
    drawDialog();
    // draw button
    ctx.drawImage(button.image, 0, button.imageShift, button.w, button.h, button.x, button.y, button.w, button.h);
    // draw button's text
    ctx.font = '22px DS-Digital';
    ctx.fillStyle = '#ffffff';
    ctx.fillText('next/hide/show', 400, 465);
    ctx.fillText('dialog', 400, 500);
}
// -------------------------------------------------------------
// 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/stars.jpg';
    backgroundImage.onload = function() {
    }
    backgroundImage.onerror = function() {
        console.log('Error loading the background image.');
    }
    // initialization of space ship
    var oSpShipImage = new Image();
    oSpShipImage.src = 'images/space_ship.png';
    oSpShipImage.onload = function() {
    }
    spaceShip = new SpaceShip(400, 300, 256, 256, oSpShipImage);
    // load the button sprite image
    var buttonImage = new Image();
    buttonImage.src = 'images/button.png';
    buttonImage.onload = function() {
    }
    button = new Button(310, 450, 180, 120, 'normal', buttonImage);
    $('#scene').mousedown(function(e) { // binding mousedown event (for dragging)
        var mouseX = e.layerX || 0;
        var mouseY = e.layerY || 0;
        if (!bDrawDialog &&
            mouseX > spaceShip.x-128 && mouseX < spaceShip.x-128+spaceShip.w &&
            mouseY > spaceShip.y-128 && mouseY < spaceShip.y-128+spaceShip.h) {
            spaceShip.bDrag = true;
            spaceShip.x = mouseX;
            spaceShip.y = mouseY;
        }
        // button behavior
        if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
            button.state = 'pressed';
            button.imageShift = 262;
        }
    });
    $('#scene').mousemove(function(e) { // binding mousemove event
        var mouseX = e.layerX || 0;
        var mouseY = e.layerY || 0;
        if (!bDrawDialog && spaceShip.bDrag) {
            spaceShip.x = mouseX;
            spaceShip.y = mouseY;
        }
        // button behavior
        if (button.state != 'pressed') {
            button.state = 'normal';
            button.imageShift = 0;
            if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
                button.state = 'hover';
                button.imageShift = 131;
            }
        }
    });
    $('#scene').mouseup(function(e) { // binding mouseup event
        spaceShip.bDrag = false;
        // button behavior
        if (button.state == 'pressed') {
            if (iDialogPage == 0) {
                iDialogPage++;
                bDrawDialog = !bDrawDialog;
            } else if (iDialogPage == 2) {
                iDialogPage = 0;
                bDrawDialog = !bDrawDialog;
            } else {
                iDialogPage++;
            }
        }
        button.state = 'normal';
        button.imageShift = 0;
    });
    setInterval(drawScene, 30); // loop drawScene
});

Here are several explanations about new features. 1. Drawing animated space with stars (pretty easy – we will shift image coordinates):

    iBgShiftX -= 10;
    if (iBgShiftX <= 0) {
        iBgShiftX = 1024;
    }
    ctx.drawImage(backgroundImage, 0 + iBgShiftX, 0, 1024, 768, 0, 0, 800, 600);

Hope that all rest code pretty understandable. I added comments quite anywhere.