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Lua Game Development Cookbook
Lua Game Development Cookbook

Lua Game Development Cookbook: Over 70 recipes that will help you master the elements and best practices required to build a modern game engine using Lua

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Lua Game Development Cookbook

Chapter 2. Events

In this chapter, we will cover the following recipes:

  • Processing input events with LuaSDL
  • Using the keyboard input
  • Using the relative mouse position
  • Using the absolute mouse position
  • Using timers

Introduction

Event-driven design offers a cheap and efficient way to detect user input without the need to check for input device status in each frame. A naïve approach to this is to query all input devices for changes in their state. There are many types of input devices such as keyboard, mouse, joystick, keypad controller, tablet, touch screen, and so on. LuaSDL relies on the library libSDL 1.2, which supports only basic input devices such as keyboard, mouse, and joystick. This version doesn't support the use of multiple devices of the same kind. This limitation has been removed with libSDL 2.x, which is used in LuaSDL 2. LuaSDL 2 is the successor of a former LuaSDL library and it's in the stage of early development at the time of writing. This chapter will cover the use of an older LuaSDL library, as the LuaSDL 2 interface is not so different.

Processing input events with LuaSDL

LuaSDL offers a form of platform-independent abstraction layer to these devices with an inner event pool. You only have to query the event pool for unprocessed events and, if there are any, check for the event type.

Getting ready

Before doing any event processing, your application must initialize internal event pools. This can be achieved with the SDL.SDL_Init function, where the only parameter is a bitmask representing which parts of LuaSDL you want to initialize. You can use the bitlib library for the Lua language. Another option would be to use the bit32 internal library if you are using the newer version of the Lua interpreter. The default value here is SDL.SDL_INIT_EVERYTHING, which is fine as it starts the event pool automatically. Specifically, you can use the SDL.SDL_INIT_EVENTTHREAD or SDL.SDL_INIT_VIDEO values to initialize the event pool.

A code sample can be used to initialize the LuaSDL library. It should be used right at the start of the application...

Using the keyboard input

LuaSDL offers a simple way of determining what key was pressed or released on your keyboard. Events with event types SDL.SDL_KEYDOWN and SDL.SDL_KEYUP can react to one keystroke at the time. This is usually fine during a game play. However, if you want to use keyboard shortcuts in a text input field, the previous approach would not be very efficient.

This recipe will show you how to manage keyboard input in a robust way that can be used for both situations—to control a game or to write text into an input field.

Getting ready

Let's say you need your game character to run when a Shift key is pressed. There are three key problems. The common PC keyboard has left and right Shift keys. These are two different keys with two different key symbol codes. The next thing is that you use these keys with another keyboard key which may or may not be the modifier key. The last problem is putting key states together, so you'll know if the player has pressed the Shift...

Using the relative mouse position

The relative mouse position is often used when you need unconstrained mouse movement. A typical example of such a use is a first person shooter game in a 3D environment. The relative mouse position represents how much the mouse pointer position changed in comparison with the previous state in all the axes.

Getting ready

The biggest problem with the relative mouse position is that the mouse pointer is constrained to the application window or the screen. You can solve this by centering the mouse cursor in the center of the application window after computing the relative cursor position or by using direct values from the mouse driver.

The relative mouse position has the big advantage of versatility because you can apply the mouse cursor speed modifier simply by multiplying the relative mouse position with a number. If that number is greater than 1, the mouse cursor will move faster. Multiplying by a number lesser than 1, will slow down the mouse cursor.

How to...

Using the absolute mouse position

The absolute mouse position is used primarily in window applications, where the mouse position constraints are desirable. The mouse position (0,0) corresponds to the upper-left corner of your application window. The maximum mouse position depends always on the size of the window. Take special care when the mouse cursor is outside the application window. The behavior of LuaSDL in this situation is highly dependent on the currently used operating system! In most cases, you won't get any events related to the mouse cursor motion.

The main advantage of this is that you can use the mouse cursor position reported directly by LuaSDL to precisely manipulate GUI elements inside of the application window. This approach is used also with tablet touch input devices, where you always get absolute positions.

How to do it…

The following mouse movement handler function shows a simple way to get the absolute mouse cursor position:

[SDL.SDL_MOUSEMOTION] = function...

Using timers

LuaSDL offers support for timer objects. The problematic part is the use of timers. The LibSDL library uses callback functions to call event functions. These callbacks run in another thread and the naïve approach, where you put the Lua function in the position of callback function, would lead to Lua state corruption. There is a better way to accomplish this by using the internal LuaSDL callback function that invokes a special user event.

Timers aren't very precise and they are mostly used in GUI updates. If you need more precision, you'll need to use High Precision Event Timer (HPET), which is out of the scope of this book.

Getting ready

Each timer object uses a user-defined event that contains unique timer function identifiers represented by integer values. LuaSDL offers a slightly modified version of the SDL.SDL_AddTimer function, where it accepts two parameters instead of three. The first parameter is an interval value in milliseconds. The second is the user...

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Description

This book is for all programmers and game enthusiasts who want to stop dreaming about creating a game, and actually create one from scratch. The reader should know the basics of programming and using the Lua language. Knowledge of the C/C++ programming language is not necessary, but it's strongly recommended in order to write custom Lua modules extending game engine capabilities or to rewrite parts of the Lua code into a more efficient form. Algebra and matrix operations are required in order to understand advanced topics in Chapter 4, Graphics – Legacy Method with OpenGL 1.x-2.1 and Chapter 5, Graphics – Modern Method with OpenGL 3.0+. Sample demonstrations are coupled with binary libraries for Windows and Linux operating systems for convenience.

Who is this book for?

This book is for all programmers and game enthusiasts who want to stop dreaming about creating a game, and actually create one from scratch.

What you will learn

  • Set up OpenGL graphics along with GLSL shaders
  • Use lighting and graphical effects
  • Create animated game characters using Box2D library
  • Load and use textures, fonts, and 3D models
  • Design and implement a graphical user interface
  • Integrate simple Artificial Intelligence for pathfinding
  • Implement networking support
  • Use data structures in programming
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Publication date : Jul 28, 2015
Length: 360 pages
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Language : English
ISBN-13 : 9781849515504
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Table of Contents

10 Chapters
1. Basics of the Game Engine Chevron down icon Chevron up icon
2. Events Chevron down icon Chevron up icon
3. Graphics – Common Methods Chevron down icon Chevron up icon
4. Graphics – Legacy Method with OpenGL 1.x–2.1 Chevron down icon Chevron up icon
5. Graphics – Modern Method with OpenGL 3.0+ Chevron down icon Chevron up icon
6. The User Interface Chevron down icon Chevron up icon
7. Physics and Game Mechanics Chevron down icon Chevron up icon
8. Artificial Intelligence Chevron down icon Chevron up icon
9. Sounds and Networking Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

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Full star icon Full star icon Full star icon Full star icon Half star icon 4.3
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1 star 16.7%
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CPallini Oct 01, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book covers a very appealing topic: game development with Lua.Leveraging on libSDL, OpenGL and several other libraries, illustrates, in the formof recipes, many techniques required to build yourself a game, game engine orprototype.Since the topic is wide and deep, it is a condensed book, rich of content inrelatively few pages: from directory organization, module and error handling, Luainteraction with C++, to game UI, physics, AI, sound and network communication,passing for the event driven SDL game loop, OpenGL (both the older immediate mode and the moremodern shading language).I found most of the content interesting, some recipes a bit difficult tounderstand at first (in my opinion delaying the explanation in 'how it works'section is a bit confusing), neverhtless worthy to be studied.A relatively good knowledge of Lua is required to fully understand the recipes(while proficience with modern C++ would help for actual game development).The approach is pragmatic and you have to use the companion code in order toappreciate the book and start experimenting (I should say compiling myself therequired libraries was not exactly 'a breeze' like the author claims in the book).All in all it is a solid, pragmatic, fairly advanced book: enough to make youappreciate the efforts required in game development and possibly desire to deepenyour knowledge about the related problems and techniques.
Amazon Verified review Amazon
Julie Blanchard Feb 07, 2018
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Bought for my sons Christmas presentHe loves it
Amazon Verified review Amazon
Dan Kosko Nov 27, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
quick delivery. just as described. good job
Amazon Verified review Amazon
Kiffin Gish Oct 27, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
If you've ever fantasized about creating your own fancy game but never was able to get beyond the basics, then this is the right place to begin. Starting with the first chapters, you become more familiar with the Lua programming language and what goes into a powerful gaming engine. Slowly but surely, your learn how Lua provides the ideal playground to build up a solid platform of modules and components that can be combined nicely. It's not just about the complex concepts that go into designing games but also the choice of the right programming language and how to use it effectively. By the end of the book you start mastering the more difficult concepts and can deal with all the fancy algorithms that go into good game making.
Amazon Verified review Amazon
Joel A. Sundquist Apr 19, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Great lua book. Even if you are not developing games it has some helpful performance tips
Amazon Verified review Amazon
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