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DZone > Web Dev Zone > HTML5 Game Development – Lesson 2

HTML5 Game Development – Lesson 2

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HTML5 Game Development – Lesson 2

by
Andrey Prikaznov
CORE ·
Nov. 26, 11 · Web Dev Zone ·
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Today we continue a series of articles on game development in HTML5. Today we will continue basics (and maybe even advanced basics). I going to show you how to fill objects with gradient color, draw text, use custom fonts to draw text, basic animation, and most important: ui element – Button.

Our previous article you can read here: Developing Your First HTML5 Game – Lesson 1. I going to work with our previous script – we will just enhance it. I going to draw text using custom font, animate object (square) filled with gradient color, and will draw ‘Play / Pause’ button to pausing animation.

Here are our demo and downloadable package:

Live Demo
download in package

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 2 | 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 2</h2>
            <a href="http://www.script-tutorials.com/html5-game-development-lesson-2" 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 {
    background-image:url(../images/01.jpg);
    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

var canvas, ctx;
var circles = [];
var selectedCircle;
var hoveredCircle;
var button;
var moving = false;
var speed = 2.0;

// -------------------------------------------------------------

// objects :

function Circle(x, y, radius){
    this.x = x;
    this.y = y;
    this.radius = radius;
}

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;
}
// -------------------------------------------------------------

// draw functions :

function clear() { // clear canvas function
    ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}

function drawCircle(ctx, x, y, radius) { // draw circle function
    ctx.fillStyle = 'rgba(255, 35, 55, 1.0)';

    ctx.beginPath();
    ctx.arc(x, y, radius, 0, Math.PI*2, true);
    ctx.closePath();

    ctx.fill();

    ctx.lineWidth = 1;
    ctx.strokeStyle = 'rgba(0, 0, 0, 1.0)';
    ctx.stroke(); // draw border
}

function drawScene() { // main drawScene function
    clear(); // clear canvas

    // draw the title text
    ctx.font = '42px DS-Digital';
    ctx.textAlign = 'center';
    ctx.fillStyle = '#ffffff';
    ctx.fillText('Welcome to lesson #2', ctx.canvas.width/2, 50);

    var bg_gradient = ctx.createLinearGradient(0, 200, 0, 400);
    bg_gradient.addColorStop(0.0, 'rgba(255, 0, 0, 0.8)');
    bg_gradient.addColorStop(0.5, 'rgba(0, 255, 0, 0.8)');
    bg_gradient.addColorStop(1.0, 'rgba(0, 0, 255, 0.8)');

    ctx.beginPath(); // custom shape begin
    ctx.fillStyle = bg_gradient;
    ctx.moveTo(circles[0].x, circles[0].y);
    for (var i=0; i<circles.length; i++) {
        ctx.lineTo(circles[i].x, circles[i].y);
    }
    ctx.closePath(); // custom shape end
    ctx.fill(); // fill custom shape

    ctx.lineWidth = 2;
    ctx.strokeStyle = 'rgba(0, 0, 255, 0.5)';
    ctx.stroke(); // draw border

    // reverting direction
    if (circles[0].x <= 300 || circles[0].x >= 385) {
        speed = -speed;
    }

    // central object behavior
    if (moving) {
        circles[0].x -= speed;
        circles[0].y -= speed;
        circles[1].x += speed;
        circles[1].y -= speed;
        circles[2].x += speed;
        circles[2].y += speed;
        circles[3].x -= speed;
        circles[3].y += speed;
    }

    drawCircle(ctx, circles[0].x, circles[0].y, (hoveredCircle == 0) ? 25 : 15);
    drawCircle(ctx, circles[1].x, circles[1].y, (hoveredCircle == 1) ? 25 : 15);
    drawCircle(ctx, circles[2].x, circles[2].y, (hoveredCircle == 2) ? 25 : 15);
    drawCircle(ctx, circles[3].x, circles[3].y, (hoveredCircle == 3) ? 25 : 15);

    // draw button
    ctx.drawImage(button.image, 0, button.imageShift, button.w, button.h, button.x, button.y, button.w, button.h);

    // draw text
    ctx.font = '30px DS-Digital';
    ctx.fillStyle = '#ffffff';
    ctx.fillText('Play/Pause', 135, 480);
    ctx.fillText(button.state, 135, 515);
}

// -------------------------------------------------------------

// initialization

$(function(){
    canvas = document.getElementById('scene');
    ctx = canvas.getContext('2d');

    var circleRadius = 15;
    var width = canvas.width;
    var height = canvas.height;

    // lets add 4 circles manually
    circles.push(new Circle(width / 2 - 20, height / 2 - 20, circleRadius));
    circles.push(new Circle(width / 2 + 20, height / 2 - 20, circleRadius));
    circles.push(new Circle(width / 2 + 20, height / 2 + 20, circleRadius));
    circles.push(new Circle(width / 2 - 20, height / 2 + 20, circleRadius));

    // load the guide sprite image
    buttonImage = new Image();
    buttonImage.src="images/button.png";
    buttonImage.onload = function() {
    }
    button = new Button(50, 450, 180, 120, 'normal', buttonImage);

    // binding mousedown event (for dragging)
    $('#scene').mousedown(function(e) {

        var mouseX = e.layerX || 0;
        var mouseY = e.layerY || 0;
        for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
            var circleX = circles[i].x;
            var circleY = circles[i].y;
            var radius = circles[i].radius;
            if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
                selectedCircle = i;
                break;
            }
        }

        // 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 for dragging selected circle
        var mouseX = e.layerX || 0;
        var mouseY = e.layerY || 0;
        if (selectedCircle != undefined) {
            // var canvasPosition = $(this).offset();

            var radius = circles[selectedCircle].radius;
            circles[selectedCircle] = new Circle(mouseX, mouseY,radius); // changing position of selected circle
        }

        hoveredCircle = undefined;
        for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
            var circleX = circles[i].x;
            var circleY = circles[i].y;
            var radius = circles[i].radius;

            if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
                hoveredCircle = i;
                circles[hoveredCircle] = new Circle(circleX, circleY, 25);
                break;
            }
        }

        // 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) { // on mouseup - cleaning selectedCircle
        selectedCircle = undefined;

        // button behavior
        if (button.state == 'pressed') {
            moving = !moving;
        }
        button.state = 'normal';
        button.imageShift = 0;
    });

    setInterval(drawScene, 30); // loop drawScene
});

Here are several explanations about new features. 1. We can draw text (with custom font) using next code:

    ctx.font = '42px DS-Digital';
    ctx.textAlign = 'center';
    ctx.fillStyle = '#ffffff';
    ctx.fillText('Welcome to lesson #2', ctx.canvas.width/2, 50);

2. Applying gradient color to objects:

    var bg_gradient = ctx.createLinearGradient(0, 200, 0, 400);
    bg_gradient.addColorStop(0.0, 'rgba(255, 0, 0, 0.8)');
    bg_gradient.addColorStop(0.5, 'rgba(0, 255, 0, 0.8)');
    bg_gradient.addColorStop(1.0, 'rgba(0, 0, 255, 0.8)');
    ctx.fillStyle = bg_gradient;

3. Button itself – I used one sprite image with all 3 button states. Also I added event handlers to hover/down events. Here are way of loading and drawing image at canvas:

    buttonImage = new Image();
    buttonImage.src="images/button.png";
    .......
    ctx.drawImage(image, sx, sy, sWidth, sHeight, dx, dy, width, height);

Step 4. Custom files

fonts/Ds-digib.ttf and images/button.png

Both files will available in our package

Live Demo
download in package

Separate big thanks to this book. This tell us about development of games in HTML5. Now it’s one of my favorite books :-)

HTML5 Games Development by Example: Beginner's Guide

Conclusion

Cool, isn`t it? I will be glad to see your thanks and comments. Good luck!


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