实现游戏开发中的屏幕滚动功能

文章来源：J2ME开发网
J2ME游戏开发中使用层的概念中介绍了如何在游戏开发中使用层，其中提到LayerManager的一个概念，View Window，本文将借助这个概念实现屏幕滚动的功能。
屏幕的移动效果一般我们是通过改变View Window的的位置来实现的，比如你想屏幕向右移动，那么你要调整View Window的x坐标增加相应的数值，如果想屏幕向左移动，那么调整View Window的x坐标减少相应的数值。上下移动原理一样。我们在得到用户的输入后就可以对View Window的位置进行调整然后重新绘制屏幕。
private void input()
{
int keyStates = getKeyStates();
if ((keyStates & LEFT_PRESSED) != 0)
{
if (scnX - 1 > 0)
scnX--;
}
if ((keyStates & RIGHT_PRESSED) != 0)
{
if (scnX + 1 + 140 < backgroundImage.getWidth())
scnX++;
}

}
// Method to Display Graphics
private void drawScreen(Graphics g)
{
g.setColor(0xffffff);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0x0000ff);
// display all layers
layerManager.setViewWindow(scnX, scnY, 140, 140);
layerManager.paint(g, 20, 20);
flushGraphics();
}
我们只使用一个背景图片如下：



由于程序比较简单，这里直接给出源代码不做过多的解释。

import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
public class ExampleGameCanvas extends GameCanvas implements Runnable
{
private boolean isPlay; // Game Loop runs when isPlay is true
private long delay; // To give thread consistency
private int width; // To hold screen width
private int height; // To hold screen height
private int scnX, scnY; // To hold screen starting viewpoint
// Sprites to be used
Image backgroundImage;
private Sprite backgroundSprite;
// Layer Manager
private LayerManager layerManager;
// Constructor and initialization
public ExampleGameCanvas() throws Exception
{
super(true);
width = getWidth();
height = getHeight();
scnX = 55;
scnY = 20;
delay = 20;
// Load Images to Sprites
backgroundImage = Image.createImage("/background.png");
backgroundSprite = new Sprite(backgroundImage);
layerManager = new LayerManager();
layerManager.append(backgroundSprite);
}
// Automatically start thread for game loop
public void start()
{
isPlay = true;
Thread t = new Thread(this);
t.start();
}
public void stop()
{
isPlay = false;
}
// Main Game Loop
public void run()
{
Graphics g = getGraphics();
while (isPlay == true)
{
input();
drawScreen(g);
try
{
Thread.sleep(delay);
} catch (InterruptedException ie)
{
}
}
}
// Method to Handle User Inputs
private void input()
{
int keyStates = getKeyStates();
if ((keyStates & LEFT_PRESSED) != 0)
{
if (scnX - 1 > 0)
scnX--;
}
if ((keyStates & RIGHT_PRESSED) != 0)
{
if (scnX + 1 + 140 < backgroundImage.getWidth())
scnX++;
}

}
// Method to Display Graphics
private void drawScreen(Graphics g)
{
g.setColor(0xffffff);
g.fillRect(0, 0, getWidth(), getHeight());
g.setColor(0x0000ff);
// display all layers
layerManager.setViewWindow(scnX, scnY, 140, 140);
layerManager.paint(g, 20, 20);
flushGraphics();
}
}

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class SimpleScrollingLayerManger extends MIDlet
{
private Display display;
public void startApp()
{
try
{
display = Display.getDisplay(this);
ExampleGameCanvas gameCanvas = new ExampleGameCanvas();
gameCanvas.start();
display.setCurrent(gameCanvas);
} catch (Exception ex)
{
System.out.println(ex);
}
}
public Display getDisplay()
{
return display;
}
public void pauseApp()
{
}
public void destroyApp(boolean unconditional)
{
exit();
}
public void exit()
{
System.gc();
destroyApp(false);
notifyDestroyed();
}
}