关于手机游戏中的炮弹轨迹—抛物线(1)

import java.io.IOException;

import javax.microedition.lcdui.Graphics;

import javax.microedition.lcdui.Image;

import javax.microedition.lcdui.game.GameCanvas;

import javax.microedition.lcdui.game.Sprite;

import javax.microedition.lcdui.game.TiledLayer;
public class MyCanvas extends GameCanvas implements Runnable

{

//小船的位置

int x,y;

//小船精灵

Sprite ship;

//地图

TiledLayer background;

//图片

Image ship_IMG, sea_IMG, bullet_IMG;

//炮弹

Bullets bullets;

public MyCanvas()

{

super(true);

//初始化船的位置

x = 10;

y = 60;

try

{

ship_IMG = Image.createImage("/ship.png");

sea_IMG = Image.createImage("/sea.png");

bullet_IMG = Image.createImage("/bullet.png");

}

catch (IOException e)

{

e.printStackTrace();

}

//初始化炮弹

bullets = new Bullets(bullet_IMG);

//初始化小船

ship = new Sprite(ship_IMG, 24, 30);

ship.setPosition(x, y);

//初始化地图

background = new TiledLayer(20, 6, sea_IMG, 32, 32);

background.createAnimatedTile(1);

int[][] map = new int[][]

{

{ 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 },

{ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
-1, -1, -1, -1, -1 },

{ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
-1, -1, -1, -1, -1 },

{ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
-1, -1, -1, -1, -1 },

{ -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
-1, -1, -1, -1, -1 },

{ 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6 }

};

//绘制地图

for(int i = 0 ; i < map.length ; i ++)

{

for(int j = 0 ; j < map[i].length ; j++)

{

background.setCell(j, i, map[i][j]);

}

}

Thread th = new Thread(this);

th.start();

}
private int k = 0;

public void run()

{

Graphics g = getGraphics();

while(true)

{

//显示出水的流动

k++;

if(k==10)

{

if(background.getAnimatedTile(-1) == 1)

{

background.setAnimatedTile(-1, 2);

}

else if(background.getAnimatedTile(-1) == 2)

{

background.setAnimatedTile(-1, 1);

}

k = 0;

}

//主控制

support(g);

//绘制

draw(g);

try

{

Thread.sleep(35);

}

catch (InterruptedException e)

{

e.printStackTrace();

}

}

}



public void support(Graphics g)

{

//控制船的移动及发射

int keyCode = getKeyStates();

switch(keyCode)

{

case UP_PRESSED:

y = Math.max(0, y - 2);

if(ship.getFrame() >= 2)

ship.setFrame(0);

else

ship.nextFrame();

break;

case DOWN_PRESSED:

y = Math.min(getHeight(), y + 2);

if(ship.getFrame() <= 2 || ship.getFrame() >= 5)

ship.setFrame(3);

else

ship.nextFrame();

break;

case LEFT_PRESSED:

x = Math.max(0, x - 2);

if(ship.getFrame() <= 5 || ship.getFrame() >= 8)

ship.setFrame(6);

else

ship.nextFrame();

break;

case RIGHT_PRESSED:

x = Math.min(getWidth(), x + 2);

if(ship.getFrame() <= 8 || ship.getFrame() >= 11)

ship.setFrame(9);

else

ship.nextFrame();

break;

case FIRE_PRESSED:

if(!bullets.isfire)

{

bullets.isfire = true;

bullets.setPoint(x+13,y);

}

break;

}

ship.setPosition(this.x, this.y);

}



/**

* 绘制

* @param g

*/

public void draw(Graphics g)

{

g.setColor(0xffffff);

g.fillRect(0,0,this.getWidth(),this.getHeight());

g.setColor(0x000000);

background.paint(g);

bullets.drawBullets(g);

ship.paint(g);

flushGraphics();

}

}

/**

* 炮弹

* <p>Title: Bullets</p>

* <p>Description: </p>

* <p>Copyright: Copyright (c) 2005</p>

* <p>Date: 2006-3-2</p>

* @author ZGY

* @version 1.0

*/

class Bullets extends Sprite

{

boolean isfire = false;

//炮弹的发射点

int bulletX, bulletY;

//炮弹的射程

int shotWidth = 50;

//炮弹的射程高度

int shotHeight = shotWidth/2-10;

//炮弹的速度

int shotSpeed = 3;

//炮弹抛物线的系数

double a,b,c;

public Bullets(Image image)

{

super(image, 15, 15);

}



/**

* 初始化炮弹

* @param x

* @param y

*/

public void setPoint(int x, int y)

{

//初始化炮弹的发射点

this.bulletX = x;

this.bulletY = y;

//根据炮弹的发射点、高度、射程计算出炮弹抛物线的三点

int x1 = bulletX;

int y1 = bulletY;

int x2 = bulletX+shotWidth/2;

int y2 = bulletY-shotHeight;

int x3 = bulletX+shotWidth;

int y3 = bulletY;

//根据抛物线方程ax^2+bx+c=y，得方程组

//ax1^2+bx1+c=y1

//ax2^2+bx2+c=y2

//ax3^2+bx3+c=y3

//解方程组得抛物线的a,b,c

b = ((y1-y3)*(x1*x1-x2*x2)-(y1-y2)*(x1*x1-x3*x3))/((x1-x3)*
(x1*x1-x2*x2)-(x1-x2)*(x1*x1-x3*x3));

a = ((y1-y2)-b*(x1-x2))/(x1*x1-x2*x2);

c = y1-a*x1*x1-b*x1;

}



/**

* 绘出炮弹

* @param g

*/

public void drawBullets(Graphics g)

{

if(isfire)

{

int k = (int)(a*bulletX*bulletX+b*bulletX+c);

setPosition(bulletX, k);

paint(g);

//炮弹的速度

bulletX += shotSpeed;

//炮弹将消失于小船的水平线

if(k > bulletY)

{

nextFrame();

if(getFrame() == 2)

{

isfire = false;

setFrame(0);

}

}

}

}

}