Sprite Animation for Game Programming
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Video games represent the first truly interactive art form. When you think about it, there aren't many paintings, sculptures, or musical compositions that allow you to interact with them and change them in any way. Video games allow their creators to share something more with the game player by giving the player a chance to put part of themselves into a game, and then see what comes out. In fact, the best games are the ones that allow the player to express their own unique style and technique when playing the game, while at the same time being entertained by the game designer's vision of an imaginary world portrayed by the game.
I'm sure you already know that computer programming is a challenging, yet rewarding endeavor that gives you the freedom to do some interesting things within the context of a computer. To create even a simple game, you must understand how to write code to draw bitmapped graphics, carry out sprite animation, play sampled digital sound effects, and process user input from a keyboard, mouse, and/or joystick. If these tasks sound somewhat overwhelming, it's because they are if you aren't properly prepared to tackle them.
This book tackles each game programming discipline one at a time, and in a manner that allows you to build one skill on top of the previous one you just learned. The end result is that you start with a few fundamental game programming skills and slowly build up a base of knowledge that allows you to tackle increasingly more complex games. The significance of this approach is that it allows you to ease into game programming a step at a time, with a focus on ramping up your skills throughout the book to tackle more challenging projects.
— Michael Morrison
You've spent a great deal of time throughout the book thus far assembling a game engine and learning the ropes of what it takes to build games. You've even created a complete game, although it didn't involve any animation. In this hour, you embark on your next complete game, which takes what you've learned about sprites and puts it to use. The Henway game developed in this hour uses several sprites and most of the sprite features built in to the game engine. The game is somewhat of a takeoff on the classic Frogger game, and it represents a significant milestone in your game programming quest because it is such an interesting little game. This is the kind of game that you can use as the basis for your own game development efforts.
In this hour, you'll learn:
Why modeling a game on a classic arcade game is sometimes a good idea
How to design a game called Henway that is somewhat of a takeoff on Frogger
How to write the code for the Henway game
Why testing a game of your own is often the most fun part of the development process
How Does the Game Play?
The original Frogger arcade game involved a frog whose goal was to make it across a highway and a river safely. Several obstacles appeared in the frog's path, including speeding cars, treacherous rushing water, and alligators, to name a few. Frogger played vertically, which means that you guided the frog from the bottom of the game screen to the top of the screen in order to reach safety. As you guided more and more frogs safely across, the game progressed to get more difficult by adding more cars and other obstacles to the mix. Although Frogger is certainly an incredibly simple game by modern gaming standards, it's a perfect example of a classic game with fun game play. This makes it a perfect candidate for creating a game of your ownjust put a twist on the concept, and you can create your own Frogger-like masterpiece.
In case you're wondering, I don't generally encourage basing all of your games on existing classics, but I have found that popular games of the past can provide good ideas for new games. These days everyone is busy trying to model computer games after movies, but not everyone is interested in playing a heavily scripted drama. Sometimes it's fun to fire up a game and play for a few minutes as a light diversion; in which case, the classics are perfect.
The popularity of Frogger resulted in a variety of knock-off games being created to coattail Frogger's success. One of these games was called Freeway, and it involved a chicken trying to cross a busy highway. Freeway was made by Activision for the Atari 2600 game system, which was the first console system to really hit it big. As a proud owner and player of Freeway, I thought it would be fun to create a similar game in this hour. However, the game you create is called Henway, which comes from an old joke. If you've never heard the joke, it goes like this: You mention the word "henway" a few times in a conversation with a friend, and eventually he'll get up the nerve to say, "What's a henway?" And you immediately respond, "Oh, about three pounds." I know, it's a very bad joke, but it makes for a fun name for a game involving a chicken and a highway.
Unlike Frogger, the hero in Henway is a chicken who desperately needs to get from one side of a busy highway to the other. Also unlike Frogger, Henway plays horizontally, which means that you guide the chicken from the left side of the screen to the right side. So, the game screen looks something like the drawing in Figure 12.1.
Figure 12.1 The Henway game consists of a Start Area, a Highway, and a Finish Area, along with chicken and car sprites.
As you can see, the obstacles working against the chicken are four sprites that are cruising up and down four lanes of highway. The cars move at varying speeds, which makes it a little trickier to time the chicken's crossing. Unlike Frogger, which requires you to guide the frog into specific zones of the Finish Area, Henway just requires you to get the chicken across the road.
You'll notice that a common thread throughout all of the game examples in the book is simplicity. Although there are all kinds of neat ways to improve on the games, I opted to leave it up to you to make the improvements. My goal is to provide you with a working game that is simple enough to understand, and then you can jazz it up with extra features.
You start the Henway game with a limited number of chickens: three. When all of your chickens get run over, the game is over. It's important to show somewhere on the screen how many chickens you have remaining. Additionally, some kind of notification should take place to inform you when you lose a chicken, as well as when you successfully make it across the highway. It also wouldn't hurt to have some kind of scoring system for rewarding good game play.
The Henway game is well suited for both keyboard and joystick input, although there isn't really a good way to use the mouse in the game. For this reason, you'll focus on supporting the keyboard and joystick, and skip the mouse entirely.