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Supercharged JavaScript Graphics

Cover of Supercharged JavaScript Graphics by Raffaele Cecco Published by O'Reilly Media, Inc.
  1. Supercharged JavaScript Graphics
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. Preface
      1. Audience and Assumptions
      2. Organization
      3. Conventions Used in This Book
      4. Using Code Examples
      5. Safari® Books Online
      6. How to Contact Us
      7. Acknowledgments
    3. 1. Code Reuse and Optimization
      1. Keeping It Fast
      2. What and When to Optimize
      3. Homespun Code Profiling
      4. Optimizing JavaScript
      5. Optimizing jQuery and DOM Interaction
      6. Other Resources
    4. 2. DHTML Essentials
      1. Creating DHTML Sprites
      2. Converting into a jQuery Plug-in
      3. Timers, Speed, and Frame Rate
      4. Internet Explorer 6 Background Image Caching
    5. 3. Scrolling
      1. CSS-Only Scrolling Effects
      2. Scrolling with JavaScript
    6. 4. Advanced UI
      1. HTML5 Forms
      2. Using JavaScript UI Libraries
      3. Creating UI Elements from Scratch
    7. 5. Introduction to JavaScript Games
      1. Game Objects Overview
      2. The Game Code
    8. 6. HTML5 Canvas
      1. Canvas Support
      2. Bitmaps, Vectors, or Both?
      3. Canvas Limitations
      4. Canvas Versus SVG
      5. Canvas Versus Adobe Flash
      6. Canvas Exporters
      7. Canvas Drawing Basics
      8. Animating with Canvas
      9. Canvas and Recursive Drawing
      10. Replacing DHTML Sprites with Canvas Sprites
      11. A Graphical Chat Application with Canvas and WebSockets
    9. 7. Vectors for Games and Simulations
      1. Operations on Vectors
      2. Creating a JavaScript Vector Object
      3. A Cannon Simulation Using Vectors
      4. Rocket Simulation
    10. 8. Google Visualizations
      1. Limitations
      2. Chart Glossary
      3. Image Charts
      4. Interactive Charts
    11. 9. Reaching the Small Screen with jQuery Mobile
      1. jQuery Mobile
      2. TilePic: A Mobile-Friendly Web Application
      3. PhoneGap
    12. 10. Creating Android Apps with PhoneGap
      1. Installing PhoneGap
      2. Creating a PhoneGap Project in Eclipse
    13. Index
    14. About the Author
    15. Colophon
    16. SPECIAL OFFER: Upgrade this ebook with O’Reilly
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Rocket Simulation

The following rocket simulation (Figure 7-6) is a more elaborate demonstration of the use of vectors. The simulation features a steerable rocket and colorful obstacles to avoid. The rocket rotates to face the mouse pointer, and you can apply engine thrust in the facing direction of the rocket by holding down the left mouse button. The simulation is gravity and friction-free, so it requires dexterous use of the mouse to keep the rocket traveling in the desired direction. The same vector object we defined earlier in the cannon example is used throughout.

Rocket simulation in action

Figure 7-6. Rocket simulation in action

The Game Object

We use functional inheritance in the rocket simulation to create both the rocket and obstacles from a base object called gameObject, which provides common methods and properties:

var gameObject = function (x, y, radius, mass) {
    var that = {
        x: x,
        y: y,
        vel: vector2d(0, 0),
        radius: radius,
        mass: mass,
        removeMe: false,

        move: function () {
            that.x += that.vel.vx;
            that.y += that.vel.vy;
            if (that.vel.vx < 0 && that.x < −50) {
                that.x += canvas.width + 100;
            } else if (that.vel.vx > 0 && that.x > canvas.width + 50) {
                that.x −= canvas.width + 100;
            }
            if (that.vel.vy < 0 && that.y < −50) {
                that.y += canvas.height + 100;
            } else if (that.vel.vy > 0 && that.y > canvas.height + 50) {
                that.y −= canvas.height + 100;
            }
        },

        draw: function () {
            return;
        }
    };
    return that;
};

Essentially, ...

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