J2ME在移动设备上实现动画程序方法
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任何动画的最基本的前提,是要在足够快的时间内显示和更换一张张的图片,让人的眼睛看到动的画面效果。图片必须按照顺序画出来。从一张图片到下一张图片之间的变化越小,效果会越好。
首先要做的,是使用你的图片处理软件(比如ps或者firework)创建一系列相同大小的图片来组成动画。每张图片代表动画一帧。你需要制作一定数量的祯--越多的帧会让你的动画看上去越平滑。制作好的图片一定要保存成PNG(Portable Network Graphics)格式,MIDP唯一支持的图片格式。
有两个办法让你刚做好的图片在MIDlet上变成动画。第一,把图片都放到一个web服务器上,让MIDlet下载他们,MIDP内置的HTTP支持。第二个办法更简单,把图片用MIDlet打包成jar文件。如果你使用的是J2ME开发工具,把PNG文件放你的项目文件里面就可以了。
动画的过程其实更像帐本记录:显示当前帧,然后适当地更换到下一帧。那么使用一个类来完成这个工作应该是很恰当的,那好,我们就先定义一个AnimatedImage类:
import .*;
import i.*;
// 定义了一个动画,该动画其实只是一系列相同大小的图片
// 轮流显示,然后模拟出的动画
public class AnimatedImage extends TimerTask {;
private Canvas canvas;
private Image[] images;
private int[][] clipList;
private int current;
private int x;
private int y;
private int w;
private int h;
// Construct an animation with no canvas.
public AnimatedImage( Image[] images ){;
this( null, images, null );
};
// Construct an animation with a null clip list.
public AnimatedImage( Canvas canvas, Image[] images )
{;
this( canvas, images, null );
};
// Construct an animation. The canvas can be null,
// but if not null then a repaint will be triggered
// on it each time the image changes due to a timer
// event. If a clip list is specified, the image is
// drawn multiple times, each time with a different
// clip rectangle, to simulate transparent parts.
public AnimatedImage( Canvas canvas, Image[] images, int[][] clipList ){;
as = canvas;
es = images;
List = clipList;
if( images != null && clipList != null ){;
if( th < th ){;
throw new IllegalArgumentException();
};
};
if( images != null && th > 0 ){;
w = images[0]idth();
h = images[0]eight();
};
};
// Move to the next frame, wrapping if necessary.
public void advance( boolean repaint ){;
if( current >= th ){;
current = 0;
};
if( repaint && canvas != null && own() ){;
int( x, y, w, h );
iceRepaints();
};
};
copy, otherwise
// set the clipping rectangle accordingly and
// draw the image multiple times.
public void draw( Graphics g ){;
if( w == 0 || h == 0 ) return;
int which = current;
if( clipList == null || clipList[which] == null ){;
Image( images[which], x, y,
| );
}; else {;
int cx = lipX();
int cy = lipY();
int cw = lipWidth();
int ch = lipHeight();
int[] list = clipList[which];
for( int i = 0; i 3 <= th; i =4 ){;
lip( x list[0], y list[1], list[2], list[3] );
Image( images[which], x, y,
| );
};
lip( cx, cy, cw, ch );
};
};
// Moves the animation′s top left corner.
public void move( int x, int y ){;
this.x = x;
this.y = y;
};
// Invoked by the timer. Advances to the next frame
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// and causes a repaint if a canvas is specified.
public void run(){;
if( w == 0 || h == 0 ) return;
advance( true );
};
};
你实例化一个AnimatedImage对象的时候你必须给AnimatedImage类的构造方法传一个Image对象数组,该数组代表动画的每一帧。使用的所有图片必须具有相同的高度和宽度。
用teImage()方法从jar文件里面加载图片:
private Image[] loadFrames( String name, int frames )
throws IOException {;
Image[] images = new Image[frames];
for( int i = 0; i < frames; i ){;
images = teImage( name i ".png" );
};
return images;
};
你也可以传递一个Canvas对象(可选),和一个剪辑列表(clip list)。如果你指定了一个canvas和使用一个timer来自动更换到动画的下一帧,就如下面的例子代码中一样,canvas在动画向前滚动以后自动被重画(repaint)。不过这样的实现办法是可选的,你可以这样做,也可以让程序选择合适的时候重画canvas。
因为MIDP 1.0不支持透明的图片,AnimatedImage 类使用一个剪辑列表来模拟透明的效果,剪辑列表是图片被剪成的方块区域的系列。图片被画出来的时候分开几次,每次画一个剪辑列表里面的剪辑区域。剪辑列表在帧的基础上被定义好,所以你需要为图片的每一帧创建一个数组。数组的大小应该是4的倍数,因为每一个剪辑面积保持了四个数值:左坐标,顶坐标,宽度以及高度。坐标的'原点是整个图片的左上角。需要注意的是使用了剪辑列表会使动画慢下来。如果图片更加复杂的话,你应该使用矢量图片。
AnimatedImage类扩展了rTask,允许你设定一个timer。这里有个例子说明如何使用timer做动画:
Timer timer = new Timer();
AnimatedImage ai = ..... // get the image
dule( ai, 200, 200 );
每隔大约200毫秒,timer调用()方法一次,这个方法使得动画翻滚到下一个帧。现在我们需要的是让MIDlet来试试显示动画!我们定义一个简单的Canvas类的子类,好让我们把动画“粘贴上去”。
import .*;
import i.*;
// A canvas to which you can attach one or more
// animated images. When the canvas is painted,
it cycles through the animated images and asks
// them to paint their current image.
public class AnimatedCanvas extends Canvas {;
private Display display;
private Image offscreen;
private Vector images = new Vector();
public AnimatedCanvas( Display display ){;
lay = display;
// If the canvas is not double buffered by the
// system, do it ourselves...
if( !isDoubleBuffered() ){;
offscreen = teImage( getWidth(),
getHeight() );
};
};
// Add an animated image to the list.
public void add( AnimatedImage image ){;
lement( image );
};
// Paint the canvas by erasing the screen and then
// painting each animated image in turn. Double
// buffering is used to reduce flicker.
protected void paint( Graphics g ){;
Graphics saved = g;
if( offscreen != null ){;
g = raphics();
};
olor( 255, 255, 255 );
Rect( 0, 0, getWidth(), getHeight() );
int n = ();
for( int i = 0; i < n; i ){;
AnimatedImage img = (AnimatedImage)
entAt( i );
( g );
};
if( g != saved ){;
Image( offscreen, 0, 0,
| );
};
};
};
AnimatedCanvas 类的代码相当简单,由一个动画导入方法和一个paint方法。canvas画布每次被画,背景都会被擦除然后循环每个导入的AnimatedImage对象,直接画到自己身上来(自己扩展了canvas类)。
import .*;
import .*;
import i.*;
import et.*;
// MIDlet that displays some simple animations.
// Displays a series of birds on the screen and
// animates them at different (random) rates.
public class AnimationTest extends MIDlet
implements CommandListener {;
private static final int BIRD_FRAMES = 7; 软件开发网
private static final int NUM_BIRDS = 5;
private Display display;
private Timer timer = new Timer();
private AnimatedImage[] birds;
private Random random = new Random();
public static final Command exitCommand = new Command( "Exit",, 1 );
public AnimationTest(){; };
public void commandAction( Command c,Displayable d ){;
if( c == exitCommand ){;
exitMIDlet();
};
};
protected void destroyApp( boolean unconditional )
throws MIDletStateChangeException {;
exitMIDlet();
};
public void exitMIDlet(){;
el(); // turn it off...
notifyDestroyed();
};
// Generate a non-negative random number...
private int genRandom( int upper ){;
return( ( Int() ) % upper );
};
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