用J2ME在移動設備上實現動畫1_JSP教程

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使用MIDP(Mobile Information Device Profile)的開發人員經常會抱怨用些什么辦法才可以在一個MIDlet上顯示動畫。 MIDP 1.0 沒有直接提供對動畫的支持(正在開發中的MIDP 2.0支持)，但真要是自己去實現，其實也并非是一件很難的事。

任何動畫的最基本的前提，是要在足夠快的時間內顯示和更換一張張的圖片，讓人的眼睛看到動的畫面效果。圖片必須按照順序畫出來。從一張圖片到下一張圖片之間的變化越小，效果會越好。

首先要做的，是使用你的圖片處理軟件（比如ps或者firework）創建一系列相同大小的圖片來組成動畫。每張圖片代表動畫一幀。需要制作一定數量的禎－－越多的幀會讓你的動畫看上去越平滑。制作好的圖片一定要保存成PNG(Portable Network Graphics)格式，MIDP唯一支持的圖片格式；有兩個辦法讓你剛做好的圖片在MIDlet上變成動畫。第一，把圖片都放到一個web服務器上，讓MIDlet下載他們，MIDP內置的HTTP支持。第二個辦法更簡單，把圖片用MIDlet打包成jar文件。如果你使用的是J2ME開發工具，把PNG文件放入你的項目文件里面就可以了。

動畫的過程其實更像帳本記錄：顯示當前幀，然后適當地更換到下一幀。那么使用一個類來完成這個工作應該是很恰當的，那好，我們就先定義一個AnimatedImage類：

import java.util.*;

import javax.microedition.lcdui.*;

// 定義了一個動畫，該動畫其實只是一系列相同大小的圖片

// 輪流顯示，然后模擬出的動畫

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 ){;

this.canvas = canvas;

this.images = images;

this.clipList = clipList;

if( images != null && clipList != null ){;

if( clipList.length < images.length ){;

throw new IllegalArgumentException();

};

};

if( images != null && images.length > 0 ){;

w = images[0].getWidth();

h = images[0].getHeight();

};

};

// Move to the next frame, wrapping if necessary.

public void advance( boolean repaint ){;

if( current >= images.length ){;

current = 0;

};

if( repaint && canvas != null && canvas.isShown()

){;

canvas.repaint( x, y, w, h );

canvas.serviceRepaints();

};

};

// Draw the current image in the animation. If

// no clip list, just a simple 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

){;

g.drawImage( images[which], x, y,

g.TOP | g.LEFT );

}; else {;

int cx = g.getClipX();

int cy = g.getClipY();

int cw = g.getClipWidth();

int ch = g.getClipHeight();

int[] list = clipList[which];

for( int i = 0; i 3 <= list.length; i =

4 ){;

g.setClip( x list[0], y list[1],

list[2], list[3] );

g.drawImage( images[which], x, y,

g.TOP | g.LEFT );

};

g.setClip( 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

// and causes a repaint if a canvas is specified.

public void run(){;

if( w == 0 || h == 0 ) return;

advance( true );

};

};

你實例化一個AnimatedImage對象的時候你必須給AnimatedImage類的構造方法傳一個Image對象數組，該數組代表動畫的每一幀。

// 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 );

};

public AnimatedImage( Canvas canvas, Image[] images,

int[][] clipList ){;

this.canvas = canvas;

this.images = images;

this.clipList = clipList;

if( images != null && clipList != null ){;

if( clipList.length < images.length ){;

throw new IllegalArgumentException();

};

};

if( images != null && images.length > 0 ){;

w = images[0].getWidth();

h = images[0].getHeight();

};

};

// Move to the next frame, wrapping if necessary.

public void advance( boolean repaint ){;

if( current >= images.length ){;

current = 0;

};

if( repaint && canvas != null && canvas.isShown()

){;

canvas.repaint( x, y, w, h );

canvas.serviceRepaints();

};

};

// Draw the current image in the animation. If

// no clip list, just a simple 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;

int[] list = clipList[which];

for( int i = 0; i 3 <= list.length; i =

4 ){;

g.setClip( x list[0], y list[1],

list[2], list[3] );

g.drawImage( images[which], x, y,

g.TOP | g.LEFT );

};

g.setClip( 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

// and causes a repaint if a canvas is specified.

public void run(){;

if( w == 0 || h == 0 ) return;

advance( true );

};

};

你實例化一個AnimatedImage對象的時候你必須給AnimatedImage類的構造方法傳一個Image對象數組，該數組代表動畫的每一幀。

// 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 );

};

public AnimatedImage( Canvas canvas, Image[] images,

int[][] clipList ){;

this.canvas = canvas;

this.images = images;

this.clipList = clipList;

if( images != null && clipList != null ){;

if( clipList.length < images.length ){;

throw new IllegalArgumentException();

};

};

if( images != null && images.length > 0 ){;

w = images[0].getWidth();

h = images[0].getHeight();

};

};

// Move to the next frame, wrapping if necessary.

public void advance( boolean repaint ){;

if( current >= images.length ){;

current = 0;

};

if( repaint && canvas != null && canvas.isShown()

){;

canvas.repaint( x, y, w, h );

canvas.serviceRepaints();

};

};

// Draw the current image in the animation. If

// no clip list, just a simple 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;

int[] list = clipList[which];

for( int i = 0; i 3 <= list.length; i =

4 ){;

g.setClip( x list[0], y list[1],

list[2], list[3] );

g.drawImage( images[which], x, y,

g.TOP | g.LEFT );

};

g.setClip( 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

// and causes a repaint if a canvas is specified.

public void run(){;

if( w == 0 || h == 0 ) return;

advance( true );

};

};

你實例化一個AnimatedImage對象的時候你必須給AnimatedImage類的構造方法傳一個Image對象數組，該數組代表動畫的每一幀。

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