HTML5与JavaScript高级游戏开发指南

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"Advanced Game Design with HTML5 and JavaScript" 是一本深入探讨如何使用HTML5和JavaScript进行高级游戏设计的书籍。书中涵盖了从基础到高级的游戏开发技术，包括Canvas绘图API、游戏资产处理、精灵与场景图的创建、物体移动、交互性实现、碰撞检测、游戏增强效果、Web Audio API的声音集成、缓动动画以及自建游戏引擎等内容。在"Chapter 1: Level Up!"中，作者可能介绍了游戏设计的基础概念，如何规划游戏关卡，以及HTML5和JavaScript在游戏开发中的重要性。这章节可能引导读者了解游戏设计的基本流程，并为后续章节的学习打下基础。 "Chapter 2: The Canvas Drawing API"详细讲解了HTML5 Canvas元素提供的绘图接口，如何绘制图形、处理颜色、变换等，这是构建2D游戏画面的关键。读者将学习到如何利用这些API来创建动态的游戏场景。 "Chapter 3: Working with Game Assets"则涉及游戏中的图像、音频和其他资源的管理。作者可能会讲述如何优化和加载游戏资产，以及使用各种工具进行资源的预处理。 "Chapter 4: Making Sprites and a Scene Graph"专注于精灵（Sprites）的概念，这是游戏中可移动对象的表示方式。同时，场景图（Scene Graph）是组织和管理游戏对象层次关系的方法，能够提高性能和简化逻辑。 "Chapter 5: Making Things Move"深入探讨了游戏中的物体运动机制，包括物理规则、速度、加速度和碰撞响应，帮助开发者实现真实感的游戏动态。 "Chapter 6: Interactivity"关注游戏的用户交互，比如事件处理、键盘和鼠标输入、触摸屏支持，让玩家能够与游戏世界互动。 "Chapter 7: Collision Detection"是游戏开发中的关键部分，书中会介绍不同的碰撞检测算法，如轴对齐边界框（AABB）、射线检测等，确保游戏中的碰撞反应准确无误。 "Chapter 8: Juice It Up"可能讲解如何通过特效、动画和反馈提升游戏体验，使游戏更具吸引力。 "Chapter 9: Sound with the Web Audio API"涵盖了Web Audio API的使用，包括音频播放控制、音效合成和处理，以及与游戏交互的同步。 "Chapter 10: Tweening"介绍了缓动（Tweening）技术，用于平滑物体的过渡效果，增加游戏视觉流畅性。 "Chapter 11: Make Your Own Game Engine"指导读者如何构建自己的游戏引擎框架，整合前面学到的技术，提高代码复用性和项目扩展性。 "Appendix A: Vectors for Movement and Collision Detection"提供了关于向量的详细解释，向量在游戏中的运动计算和碰撞检测中起着核心作用。这本书旨在通过实例和实践，帮助读者掌握HTML5和JavaScript开发高级2D游戏的全面技能。无论是初学者还是有经验的开发者，都能从中获得宝贵的知识和实践经验。

CHAPTER 1 ■ LEVEL UP!

Note ■ Object.keys will return only what’s known as an object’s enumerable properties. An enumerable

property is just any ordinary property that you can see in an object. And those are usually the only ones you care

about. But an object can also have hidden properties, which are called nonenumerable. Object.keys won’t

display them, and if you need to know how to make a property nonenumerable, you’ll learn how later in

this chapter. If you need to view nonenumerable properties, use Object.getOwnPropertyNames instead

of Object.keys

Here’s a practical example of how to use object keys. Imagine that you’re making an adventure game,

using room objects. Your room objects maintain the state of a room in the game, as well as what the room

contains:

let room = {

door: "open",

light: "on",

contents: ["carpet", "mouse", "katana"]

};

You can see that the room has three properties. You can view these properties as an array of strings with

this syntax:

console.log(Object.keys(room));

Here’s what this displays:

["door", "light", "contents"]

That’s interesting, but not useful—yet. Object.keys becomes really useful when you combine it with

forEach:

Object.keys(room).forEach(key => {

let value = room[key];

console.log("key: " + key + ", value: " + value);

});

That code will display the following:

key: door, value: open

key: light, value: on

key: contents, value: carpet,mouse,katana

You can access the property name by key and the property value with value. It will now be really easy to

apply any game logic that you need to the room, its state, or its contents.

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CHAPTER 1 ■ LEVEL UP!

Note ■ Remember, if you ever need to check whether an object contains a property, use hasOwnProperty(),

like this:

if(room.hasOwnProperty("light")) { ... }

If you prefer, you can use a for of loop to do the same thing:

let roomProperties = Object.keys(room);

for (let key of roomProperties) {

let value = room[key];

console.log("key: " + key + ", value: " + value);

}

The output is exactly the same as the first example.

But there’s another way to do this! We can use a good old-fashioned for in loop, which has been part of

JavaScript since version 1. Here’s how to use it to produce the same output as the previous examples:

for(let key in room) {

let value = room[key];

console.log("key: " + key + ", value: " + value);

}

There are two important things to be aware of if you use a for in loop. First, it doesn’t loop through

the object’s keys in any specific order. So if the order is important to you, be aware that you can’t rely on it.

Second, it will loop through keys that belong both to the object and to its prototype (see “Making Objects”

later in this chapter for more about object prototypes.) If you need to guarantee that only the object’s

own properties are being accessed, you must test for that with the object’s hasOwnProperty method in an

additional if statement.

for(let key in room) {

if (room.hasOwnProperty(key) {

let value = room[key];

console.log("key: " + key + ", value: " + value);

}

Neither of these features might be a problem, depending on the object you’re loop through and what

you want to achieve. But if you want to play it safe, the combination of Object.keys and forEach is a little

more reliable.

Looping through Only Some Array Elements

You might only want to loop through an array until you find one element that you’re looking for. When

you’ve found it, the loop should stop checking further. You can do this with a method called some. The some

method will check all the elements in the array until the callback function returns true. As soon as true is

returned, it quits.

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