Computer Graphics: 煙粒子

• Smoke.java

package onlyfun.caterpillar.graphics.particle;

import java.awt.*; 
import java.applet.*; 
import javax.swing.JApplet;
 
public class Smoke extends Applet implements Runnable { 
    private final int Max = 1000; 
    private SmokeParticle particles[]; // 煙粒子 
    private int appletWidth, appletHeight, xCenter, yCenter; 
    private Image offScreen; 
    private Graphics drawOffScreen; 
    
    public void init() {    
        setBackground(Color.black); // 背景為黑色 
 
        particles = new SmokeParticle[Max]; // 建立粒子 
 
        // 取得顯像區域 
        appletWidth = getSize().width; 
        appletHeight = getSize().height; 
 
        // 煙初始位置 
        xCenter = appletWidth/2; 
        yCenter = 2*appletHeight/3; 
        for(int i=0; i<Max; i++) 
            particles[i] = new SmokeParticle();
 
        // 建立次畫面 
        offScreen = createImage(appletWidth,appletHeight); 
        drawOffScreen = offScreen.getGraphics(); 
    } 

    public void start() { 
        new Thread(this).start(); 
    } 
 
    public void update(Graphics g) { 
        paint(g); 
    } 
 
    public void paint(Graphics g) { 
        g.drawImage(offScreen,0,0,this); 
    } 
 
    public void run() {  
        Color color; 
        
        int windTime = 0;
        double windX = 0;
        while(true) {            
            drawOffScreen.clearRect(0,0,
                      appletWidth,appletHeight); 
 
            if(windTime <=0) {
                // 風速 x
                windX = 30*Math.random()-15; 
                // 風吹時間
                windTime = (int)(20*Math.random()); 
            }
            
            for(int i = 0; i < Max; i++) {
                if(particles[i].getState()) {
                    color = particles[i].getColor();
                    
                    // 受風動的效果不一 
                    double wx =
                          windX/particles[i].getWeight();
                    double x = 
                          particles[i].getPoint().getX();
                    double y = 
                          particles[i].getPoint().getY();
                    particles[i].getPoint().setLocation(x+wx, y);

                    x = particles[i].getPoint().getX();
                    y = particles[i].getPoint().getY();

                    drawOffScreen.setColor(color); 
                    drawOffScreen.fillOval(
                                 (int) x, (int)y, 2, 2); 
                    particles[i].nextState(); 
                }                  
            } 
 
            for(int i = 0; i < Max; i++) { 
                if(!particles[i].getState()) {
                    particles[i].setLife(
                             (int)(255*Math.random()));
                    particles[i].resume(new Point(
                        (int)(xCenter+ Math.random()*10), 
                        (int)(yCenter + Math.random()*10))); 
                }
            } 
 
            // 重繪畫面 
            repaint(); 
 
            try { 
                Thread.sleep(150); 
            } 
            catch (InterruptedException e) { } 
            
            windTime--;
        } 
    } 
}
 
class SmokeParticle { 
    private Point position; // 位置 
    private double vx, vy;  // 水平與垂直速度 
    private double weight;  // 重量 
    private int life;       // 生命週期 
    private boolean state;  // 狀態 
    private Color color;    // 顏色 
    
    public void resume(Point p) { 
        position = p; 
        vx = 0; 
        vy = -1; 
        weight = 10* Math.random() + 1; 
        state = true; 
        color = new Color(life, life, life); 
    } 

    public void setLife(int life) {
        this.life = life;
    }
    
    public void setWeight(double weight) {
        this.weight = weight;
    }
    
    public Point getPoint() { 
        return position; 
    } 
 
    public double getWeight() { 
        return weight; 
    } 
 
    public Color getColor() { 
        return new Color(life, life, life); 
    } 
 
    public boolean getState() { 
        return state; 
    } 
 
    public void nextState() { 
        position.setLocation(position.getX(), 
                             position.getY() + vy);
        life -= 1; 
        
        if(life <=0) { 
            life = 0; 
            state = false; 
        } 
    } 
}