怎样在android游戏开发实现粒子爆炸效果

给大家解说怎样在android游戏开发实现粒子爆炸效果

package net.obviam.particles.model;

import android.graphics.Canvas;
import android.graphics.Rect;
import android.util.Log;

public class Explosion {

	private static final String TAG = Explosion.class.getSimpleName();
	
	public static final int STATE_ALIVE 	= 0;	// at least 1 particle is alive
	public static final int STATE_DEAD 		= 1;	// all particles are dead
	
	private Particle[] particles;			// particles in the explosion
	private int x, y;						// the explosion's origin
	private float gravity;					// the gravity of the explosion (+ upward, - down)
	private float wind;						// speed of wind on horizontal
	private int size;						// number of particles
	private int state;						// whether it's still active or not
	
	public Explosion(int particleNr, int x, int y) {
		Log.d(TAG, "Explosion created at " + x + "," + y);
		this.state = STATE_ALIVE;
		this.particles = new Particle[particleNr];
	 	for (int i = 0; i < this.particles.length; i++) {
			Particle p = new Particle(x, y);
			this.particles[i] = p;
		}
	 	this.size = particleNr;
	}
	
	public Particle[] getParticles() {
		return particles;
	}
	public void setParticles(Particle[] particles) {
		this.particles = particles;
	}
	public int getX() {
		return x;
	}
	public void setX(int x) {
		this.x = x;
	}
	public int getY() {
		return y;
	}
	public void setY(int y) {
		this.y = y;
	}
	public float getGravity() {
		return gravity;
	}
	public void setGravity(float gravity) {
		this.gravity = gravity;
	}
	public float getWind() {
		return wind;
	}
	public void setWind(float wind) {
		this.wind = wind;
	}
	public int getSize() {
		return size;
	}
	public void setSize(int size) {
		this.size = size;
	}
	
	public int getState() {
		return state;
	}

	public void setState(int state) {
		this.state = state;
	}

	// helper methods -------------------------
	public boolean isAlive() {
		return this.state == STATE_ALIVE;
	}
	public boolean isDead() {
		return this.state == STATE_DEAD;
	}

	public void update() {
		if (this.state != STATE_DEAD) {
			boolean isDead = true;
			for (int i = 0; i < this.particles.length; i++) {
				if (this.particles[i].isAlive()) {
					this.particles[i].update();
					isDead = false;
				}
			}
			if (isDead)
				this.state = STATE_DEAD; 
		}
	}
	
	public void update(Rect container) {
		if (this.state != STATE_DEAD) {
			boolean isDead = true;
			for (int i = 0; i < this.particles.length; i++) {
				if (this.particles[i].isAlive()) {
					this.particles[i].update(container);
//					this.particles[i].update();
					isDead = false;
				}
			}
			if (isDead)
				this.state = STATE_DEAD; 
		}
	}

	public void draw(Canvas canvas) {
		for(int i = 0; i < this.particles.length; i++) {
			if (this.particles[i].isAlive()) {
				this.particles[i].draw(canvas);
			}
		}
	}
}

[代码]Particle.java

package net.obviam.particles.model;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;

public class Particle {
	
	public static final int STATE_ALIVE = 0;	// particle is alive
	public static final int STATE_DEAD = 1;		// particle is dead
	
	public static final int DEFAULT_LIFETIME 	= 200;	// play with this
	public static final int MAX_DIMENSION		= 5;	// the maximum width or height
	public static final int MAX_SPEED			= 10;	// maximum speed (per update)
	
	private int state;			// particle is alive or dead
	private float widht;		// width of the particle
	private float height;		// height of the particle
	private float x, y;			// horizontal and vertical position
	private double xv, yv;		// vertical and horizontal velocity
	private int age;			// current age of the particle
	private int lifetime;		// particle dies when it reaches this value
	private int color;			// the color of the particle
	private Paint paint;		// internal use to avoid instantiation
	
	
	public int getState() {
		return state;
	}

	public void setState(int state) {
		this.state = state;
	}

	public float getWidht() {
		return widht;
	}

	public void setWidht(float widht) {
		this.widht = widht;
	}

	public float getHeight() {
		return height;
	}

	public void setHeight(float height) {
		this.height = height;
	}

	public float getX() {
		return x;
	}

	public void setX(float x) {
		this.x = x;
	}

	public float getY() {
		return y;
	}

	public void setY(float y) {
		this.y = y;
	}

	public double getXv() {
		return xv;
	}

	public void setXv(double xv) {
		this.xv = xv;
	}

	public double getYv() {
		return yv;
	}

	public void setYv(double yv) {
		this.yv = yv;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public int getLifetime() {
		return lifetime;
	}

	public void setLifetime(int lifetime) {
		this.lifetime = lifetime;
	}

	public int getColor() {
		return color;
	}

	public void setColor(int color) {
		this.color = color;
	}
	
	// helper methods -------------------------
	public boolean isAlive() {
		return this.state == STATE_ALIVE;
	}
	public boolean isDead() {
		return this.state == STATE_DEAD;
	}

	public Particle(int x, int y) {
		this.x = x;
		this.y = y;
		this.state = Particle.STATE_ALIVE;
		this.widht = rndInt(1, MAX_DIMENSION);
		this.height = this.widht;
//		this.height = rnd(1, MAX_DIMENSION);
		this.lifetime = DEFAULT_LIFETIME;
		this.age = 0;
		this.xv = (rndDbl(0, MAX_SPEED * 2) - MAX_SPEED);
		this.yv = (rndDbl(0, MAX_SPEED * 2) - MAX_SPEED);
		// smoothing out the diagonal speed
		if (xv * xv + yv * yv > MAX_SPEED * MAX_SPEED) {
			xv *= 0.7;
			yv *= 0.7;
		}
		this.color = Color.argb(255, rndInt(0, 255), rndInt(0, 255), rndInt(0, 255));
		this.paint = new Paint(this.color);
	}
	
	/**
	 * Resets the particle
	 * @param x
	 * @param y
	 */
	public void reset(float x, float y) {
		this.state = Particle.STATE_ALIVE;
		this.x = x;
		this.y = y;
		this.age = 0;
	}

	// Return an integer that ranges from min inclusive to max inclusive.
	static int rndInt(int min, int max) {
		return (int) (min + Math.random() * (max - min + 1));
	}

	static double rndDbl(double min, double max) {
		return min + (max - min) * Math.random();
	}
	
	public void update() {
		if (this.state != STATE_DEAD) {
			this.x += this.xv;
			this.y += this.yv;
			
			// extract alpha
			int a = this.color >>> 24;
			a -= 2;								// fade by 5
			if (a <= 0) {						// if reached transparency kill the particle
				this.state = STATE_DEAD;
			} else {
				this.color = (this.color & 0x00ffffff) + (a << 24);		// set the new alpha
				this.paint.setAlpha(a);
				this.age++;						// increase the age of the particle
//				this.widht *= 1.05;
//				this.height *= 1.05;
			}
			if (this.age >= this.lifetime) {	// reached the end if its life
				this.state = STATE_DEAD;
			}
			
			// http://lab.polygonal.de/2007/05/10/bitwise-gems-fast-integer-math/
			//32bit
//			var color:uint = 0xff336699;
//			var a:uint = color >>> 24;
//			var r:uint = color >>> 16 & 0xFF;
//			var g:uint = color >>>  8 & 0xFF;
//			var b:uint = color & 0xFF;
			
		}
	}
	
	public void update(Rect container) {
		// update with collision
		if (this.isAlive()) {
			if (this.x <= container.left || this.x >= container.right - this.widht) {
				this.xv *= -1;
			}
			// Bottom is 480 and top is 0 !!!
			if (this.y <= container.top || this.y >= container.bottom - this.height) {
				this.yv *= -1;
			}
		}
		update();
	}

	public void draw(Canvas canvas) {
//		paint.setARGB(255, 128, 255, 50);
		paint.setColor(this.color);
		canvas.drawRect(this.x, this.y, this.x + this.widht, this.y + this.height, paint);
//		canvas.drawCircle(x, y, widht, paint);
	}

}