fading.java

J2ME手机游戏开发技术详解,适合初学者阅读使用

/**
 *
 * By:      Oscar Wivall
 * Date:    2004-05-06
 *
 * Description: Create cool effects by fading in/out the images in MIDP 2.0.
 *              This midlet shows how to change the alpha value of an Image.
 *
 *              This MIDlet is tested on Z1010 and K700.
 *
 */


import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

import javax.microedition.io.*;
import java.io.*;

/*
*   Main class. Create TheCanvas, Add a exit button and display the canvas.
*/
public class Fading extends javax.microedition.midlet.MIDlet 
                        implements CommandListener{

    private Command mExitCommand;

    public void startApp() {

        mExitCommand = new Command("Exit", Command.SCREEN, 0);
        TheCanvas tc = new TheCanvas();
        tc.addCommand(mExitCommand);
        tc.setCommandListener(this);
        Display d = Display.getDisplay(this);
        d.setCurrent(tc);
    }

    public void pauseApp() {
        
    }

    public void destroyApp(boolean unconditional) {

    }
    
    public void commandAction(Command c, Displayable d){
        notifyDestroyed();
    }
}

/*
* TheCanvas class: loads both of the images used in this MIDlet,
*                  uses graphics do do the backbuffer drawing,
*                  uses ImageEffect do do the Image blending.
*/
class TheCanvas extends Canvas
                implements Runnable{

    private Image orangeImage;
    private Image greenImage;
    private Image mBufferImage;
    
    private Graphics mGraphics;
    
    private boolean mTrucking = true;
    private boolean mUpdate = true;
    
    private int mAlpha = 0;
    private int mValue = 5;

    private int[]rawInt; // this is the array who will hold the image ARGB values. 
                         // to do the blending we will change the Alpha value.
    
    private Runtime rt;

    public TheCanvas(){
        
        rt = Runtime.getRuntime(); // to get the amount of free memory.
        
        // Load images. Use mGraphics to draw on the backbuffer.
        mBufferImage = Image.createImage(getWidth(), getHeight());
        mGraphics = mBufferImage.getGraphics();
        try{
            orangeImage = Image.createImage("/orange.png");
            greenImage = Image.createImage("/green.png");
        }catch(Exception e){}

        // Allocate mamory for the image array.
        // Use the getRGB method to get all ARGB values from the image to the rawInt //array.
        rawInt = new int[orangeImage.getWidth() * orangeImage.getHeight()];
        orangeImage.getRGB(rawInt, 0, orangeImage.getWidth(), 0, 0, orangeImage.getWidth(), orangeImage.getHeight());
        
        Thread t = new Thread(this);
        t.start();
    }

    // draw the image to the canvas.
    public void paint(Graphics g){
        g.drawImage(mBufferImage, this.getWidth()/2, this.getHeight()/2, g.VCENTER|g.HCENTER);
        g.drawString("freeMemory=" + String.valueOf(rt.freeMemory()), 0, 100, 0);
        mUpdate = true;
    }

    public void run() {
        while(mTrucking){
            if(mUpdate){
                // change the alpha value each loop. 255=opaque, 0=transparent.
                mAlpha+= mValue;
                if(mAlpha>=255)
                    mValue = mValue *-1;
                else if(mAlpha<=0)
                    mValue = mValue *-1;

                // Use the blend method in ImageEffect the change the Alpha value.
                // create a new Image from the new rawInt array.
                ImageEffect.blend(rawInt, mAlpha);
                Image fadingImage = Image.createRGBImage(rawInt, orangeImage.getWidth(), orangeImage.getHeight(), true);

                mGraphics.setColor(0xFFFFFF);
                mGraphics.fillRect(0, 0, getWidth(), getHeight());
                mGraphics.drawImage(greenImage,this.getWidth()/2, this.getHeight()/2, Graphics.VCENTER|Graphics.HCENTER);
                mGraphics.drawImage(fadingImage,this.getWidth()/2, this.getHeight()/2, Graphics.VCENTER|Graphics.HCENTER);
                System.gc();
                
                mUpdate = false;
            }
            repaint();
        }
    }
    
}


/*
 * This class changes the alpha value of an image array.
 * All the pixels in the image contains Alpha, Red, Green, Blue (ARGB) colors
 * where each of the color is a value from 0 to 255.
 * If Alpha is 255 the pixel will be opaque, if its 0 the pixel is transparent.
 * 0xFFFF0000 = 11111111 11111111 00000000 00000000 - this is a red opaque pixel.
 *
 * To get the RGB values from the array we can use the AND '&' operator.
 * (11111101 & 01111110) = 01111100, only the 1:s where & = 1 will get through.
 *
 * to change 11111111 to 11111111 00000000 00000000 00000000 we can use the
 * shift left operator '<<', (00000001 << 7) = 10000000 in dec (1<<7) = 128
 *
 * To change the alpha value we loop through all the pixels in the image.
 *
 * With the blend method its also possible to mask and dontmask specific colors.
*/

class ImageEffect{
    
    // raw is the image array.
    public static void blend(int[] raw, int alphaValue, int maskColor, int dontmaskColor){
        int len = raw.length;
        
        // Start loop through all the pixels in the image.
        for(int i=0; i<len; i++){
            int a = 0;
            int color = (raw[i] & 0x00FFFFFF); // get the color of the pixel.
            if(maskColor==color){
                a = 0;
            }else if(dontmaskColor==color){
                a = 255;
            }else if(alphaValue>0){
                a = alphaValue;     // set the alpha value we vant to use 0-255.
            }
            
            a = (a<<24);    // left shift the alpha value 24 bits.
            // if color = 00000000 11111111 11111111 00000000
            // and alpha= 01111111 00000000 00000000 00000000
            // then c+a = 01111111 11111111 11111111 00000000
            // and the pixel will be blended.
            color += a;
            raw[i] = color;
        }
    }
    public static void blend(int[] raw, int alphaValue){
        blend(raw, alphaValue, 0xFFFFFFFF, 0xFFFFFFFF);
    }
}