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.NET Game Programming

with DirectX 9.0

ALEXANDRE SANTOS LOBÃO

AND

ELLEN HATTON

.NET Game Programming with DirectX 9.0

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CHAPTER 4

River Pla.Net:

Tiled Game Fields,

Scrolling, and

DirectAudio

I N THIS CHAPTER we’ll apply the

concepts learned in the pre-

vious chapter about Direct3D

to implement DirectX gaming

classes (such as GameEngine

and Sprite ), so we’ll easily be

able to create high-speed

graphics games. We’ll also

introduce basic DirectAudio

concepts that will allow us to

include sound effects and

background music in our

games.

We’ll also examine the

concept of tiled game fields

and scrolling in games, and

start implementing a clone of

Activision’s River Raid game, a

popular title for Atari 2600 and VCS. Our sample game, shown in Figure 4-1, will be

finished in the next chapter, where we’ll introduce DirectInput and the use of

force-feedback joysticks.

Scrolling games and tile-based games have been around since earlier video

game consoles and home computers hit the shelves, and we often see games that

use both techniques. We’ll discuss some interesting points about each in the next

sections.

211

Figure 4-1. River Pla.Net, a River Raid clone, is this chapter’s

sample game

Chapter 4

Scrolling Games

Although the basic concept of scrolling games is very simple, there are many inter-

esting variations we must consider when we start creating a new game. We can

define scrolling games as the games in which the background moves in a con-

tinuous way. It’s a very loose definition, but it’ll suffice for our goals here.

Some of the typical choices we must make when coding scrolling games are

discussed next.

Scrolling Direction

All scrolling games are either vertical scrollers, horizontal scrollers, or full scrollers,

meaning that the background on these games scroll in a vertical direction, in a

horizontal direction, or in any direction. We’ll discuss some variations of these

movements in this section.

The most common choice is to implement vertical “up-down” scrollers (as

does the sample game for this chapter), where the background moves from the top

to the bottom of the screen, and horizontal “right-left” scrollers, where the back-

ground moves from right to left. We don’t see many scrolling games using the

opposite direction schemes because using these directions makes our games seem

more natural to players.

Full scrollers are harder to implement and to play, but when made correctly,

they can lead to very interesting gameplay. Just imagine a game in which players

can move their character in any direction: This might be an interesting feature, but

the player could become disorientated, and the game objective would be less clear.

Parallax Scrolling

Parallax scrolling is an ingenious trick that gives players the feeling of being in a

3-D environment, even with flat images.

The basic idea is to create different layers of background objects, each one

moving at different speeds. For example, if we are controlling a monkey in a

jungle, we can create some bushes and trees that scroll at the same speed as the

terrain, trees a little farther off that move a little slower, distant mountains that

move very slowly, and maybe a fixed moon in the sky.

212

River Pla.Net: Tiled Game Fields, Scrolling, and DirectAudio

This approach creates a more lifelike game, but must be used with care

because it can lead to visual clutter and confusion for the player. A good tip is to

make distant objects with less vivid colors. This adds to the ambience without

distracting the player.

Player or Engine-Controlled Scrolling

When coding the scrolling for our game, we need to decide whether the back-

ground will always be moving (except, perhaps, when facing some end-of-level

bosses), if it will move depending solely on the player’s input, or if the movement

will be a combination of both.

In some scrolling games, the player is always in the same position on the

screen (usually the middle), and the background rolls according to the player’s

movement: When a player moves the joystick to the right, his or her character

walks to the right (moving in a fixed position), while the background moves to the

left. Many race games use this approach.

Some games use a similar solution: A player walks freely in a restricted area,

and when he or she gets near any border, the background starts to move until the

player starts walking back toward the center of the screen.

Some other games use a combination of automatic scrolling with player-

controlled scrolling; the player controls scrolling right or left, but is always

moving from the top to the bottom of the screen.

One last group of games comprises the auto-scrolling ones, such as the

sample we’ll code in this chapter: The background simply goes on scrolling

without player intervention, creating a nonstop action game.

Choosing the Scrolling Type

Even a topic as simple as choosing the scroll type we should use in our game may

lead to extensive discussion. Of course there’s a lot more we can do when coding

scrolling games; don’t be reluctant to try new ideas. For example, we can split the

screen and make two areas with different scrolling behaviors, such as in the old

arcade game Olympics, where the computer controls a character running in the

upper middle of the screen and the player runs in the lower middle; each half-

screen scrolls with its own speed.

The most appropriate type of scrolling will vary from game to game, and it will

be up to us to make the final choice between code complexity and game playability.

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APress - Net Game Programming With Directx 9.0 (2003).pdf

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