《Java 2D游戏编程入门》—— 8.4 用原型小行星工厂生产小行星

本节书摘来异步社区《Java 2D游戏编程入门》一书中的第8章，第8.4节，作者：【美】Timothy Wright（莱特），更多章节内容可以访问云栖社区“异步社区”公众号查看。

8.4 用原型小行星工厂生产小行星

位于javagames.prototype包中的PrototypeAsteroidFactory，包含了3个大的、3个中型的和3个小的小行星，它们都是使用编辑器并粘贴到代码中设计的。给定一个位置，这3个方法生成一个随机数来选择所返回的小行星：

createLargeAsteroid( Vector2f position )

createMediumAsteroid( Vector2f position )

createSmallAsteroid( Vector2f position )```

第一个方法mirror()，用来沿着x轴和y轴翻转模型，以便模型有多个独特的版本。

// PrototypeAsteroidFactory.java
private Vector2f[] mirror( Vector2f[] polygon ) {
Vector2f[] mirror = new Vector2f[ polygon.length ];
float x = rand.nextBoolean() ? 1.0f : -1.0f;
float y = rand.nextBoolean() ? 1.0f : -1.0f;
Matrix3x3f mat = Matrix3x3f.scale( x, y );
for( int i = 0; i polygon.length; ++i ) {
mirror[i] = mat.mul( polygon[i] );
}
return mirror;
}`
就像在执行视口矩阵乘法的时候使用矩阵来翻转y轴一样，通过乘以-1来翻转x或y轴的值，以缩放模型。

package javagames.prototype;

import java.util.Random;

import javagames.prototype.PrototypeAsteroid.Size;

import javagames.util.Matrix3x3f;

import javagames.util.Vector2f;

public class PrototypeAsteroidFactory {

private static final Vector2f[][] LARGE = {

 { // Large 0

 new Vector2f(-0.029733956f, 0.283255100f),

 new Vector2f(-0.183098610f, 0.111111104f),

 new Vector2f(-0.230046930f,-0.057902932f),

 new Vector2f(-0.092331770f,-0.139280080f),

 new Vector2f( 0.117370844f,-0.142410040f),

 new Vector2f( 0.161189320f,-0.048513293f),

 new Vector2f( 0.151799680f, 0.067292630f),

 new Vector2f( 0.195618150f, 0.129890440f),

 new Vector2f( 0.017214417f, 0.158059480f),

 }, { // Large 1

 new Vector2f(-0.001763641f, 0.325800420f),

 new Vector2f(-0.082892360f, 0.220339000f),

 new Vector2f(-0.227513200f, 0.065913380f),

 new Vector2f(-0.206349200f,-0.141242860f),

 new Vector2f(-0.061728360f,-0.080979230f),

 new Vector2f( 0.061728418f,-0.167608260f),

 new Vector2f( 0.192239940f,-0.092278720f),

 new Vector2f( 0.167548480f, 0.126177010f),

 new Vector2f( 0.107583820f, 0.269303200f),

 }, { // Large 2

 new Vector2f( 0.176838760f,-0.107981205f),

 new Vector2f(-0.070422530f,-0.076682330f),

 new Vector2f(-0.220657290f,-0.123630640f),

 new Vector2f(-0.273865400f, 0.048513293f),

 new Vector2f(-0.186228510f, 0.086071970f),

 new Vector2f(-0.214397490f, 0.223787190f),

 new Vector2f(-0.026604056f, 0.148669780f),

 new Vector2f( 0.104851365f, 0.220657290f),

 new Vector2f( 0.211267590f, 0.032863855f),

private static final Vector2f[][] MEDIUM = {

 { // Medium 0

 new Vector2f(-0.045383394f, 0.186228510f),

 new Vector2f(-0.167449180f, 0.123630700f),

 new Vector2f(-0.067292630f, 0.039123654f),

 new Vector2f(-0.107981205f,-0.073552370f),

 new Vector2f( 0.057902932f,-0.073552370f),

 new Vector2f( 0.133020280f, 0.098591566f),

 }, { // Medium 1

 new Vector2f(-0.023474216f, 0.189358350f),

 new Vector2f(-0.107981205f, 0.107981205f),

 new Vector2f(-0.129890440f,-0.098591566f),

 new Vector2f( 0.020344257f,-0.120500800f),

 new Vector2f( 0.139280080f,-0.001564979f),

 new Vector2f( 0.076682330f, 0.092331770f),

 new Vector2f(-0.007824719f, 0.095461670f),

 }, { // Medium 2

 new Vector2f(-0.064162790f, 0.158059480f),

 new Vector2f(-0.173708920f, 0.126760600f),

 new Vector2f(-0.142410040f, 0.023474216f),

 new Vector2f(-0.039123654f, 0.029733956f),

 new Vector2f( 0.010954618f,-0.035993695f),

 new Vector2f( 0.117370844f, 0.023474216f),

 new Vector2f( 0.117370844f, 0.120500800f),

 new Vector2f(-0.001564979f, 0.092331770f),

private static final Vector2f[][] SMALL = {

 { // Small 0

 new Vector2f(-0.048513293f, 0.057902990f),

 new Vector2f(-0.073552430f,-0.042253494f),

 new Vector2f( 0.004694819f,-0.035993695f),

 new Vector2f( 0.042253494f, 0.026604056f),

 new Vector2f(-0.001564979f, 0.082942130f),

 }, { // Small 1

 new Vector2f( 0.067292690f, 0.007824719f),

 new Vector2f(-0.029733956f,-0.076682330f),

 new Vector2f(-0.067292630f,-0.042253494f),

 new Vector2f(-0.061032890f, 0.082942130f),

 new Vector2f( 0.032863855f, 0.111111104f),

 }, { // Small 2

 new Vector2f(-0.007824719f, 0.089201870f),

 new Vector2f(-0.114241004f, 0.001564979f),

 new Vector2f(-0.004694819f,-0.067292690f),

 new Vector2f( 0.039123654f,-0.039123654f),

 new Vector2f(-0.014084518f, 0.020344317f),

private PolygonWrapper wrapper;

private Random rand;

public PrototypeAsteroidFactory( PolygonWrapper wrapper ) {

 this.wrapper = wrapper;

 this.rand = new Random();

public PrototypeAsteroid createLargeAsteroid( Vector2f position ) {

 PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper );

 asteroid.setPosition( position );

 asteroid.setPolygon( getRandomAsteroid( LARGE ) );

 asteroid.setSize( Size.Large );

 return asteroid;

public PrototypeAsteroid createMediumAsteroid( Vector2f position ) {

 PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper );

 asteroid.setPosition( position );

 asteroid.setPolygon( getRandomAsteroid( MEDIUM ) );

 asteroid.setSize( Size.Medium );

 return asteroid;

public PrototypeAsteroid createSmallAsteroid( Vector2f position ) {

 PrototypeAsteroid asteroid = new PrototypeAsteroid( wrapper );

 asteroid.setPosition( position );

 asteroid.setPolygon( getRandomAsteroid( SMALL ) );

 asteroid.setSize( Size.Small );

 return asteroid;

private Vector2f[] getRandomAsteroid( Vector2f[][] asteroids ) {

 return mirror( asteroids[ rand.nextInt( asteroids.length ) ] );

private Vector2f[] mirror( Vector2f[] polygon ) {

 Vector2f[] mirror = new Vector2f[ polygon.length ];

 float x = rand.nextBoolean() ? 1.0f : -1.0f;

 float y = rand.nextBoolean() ? 1.0f : -1.0f;

 Matrix3x3f mat = Matrix3x3f.scale( x, y );

 for( int i = 0; i polygon.length; ++i ) {

 mirror[i] = mat.mul( polygon[i] );

 return mirror;

RandomAsteroidExample位于javagames.prototype包中，如图8.10所示，它使用PolygonWrapper、PrototypeAsteroid和PrototypeAsteroid Factory，来生成在屏幕上随机飞来飞去的陨石。

 div img src="https://yqfile.alicdn.com/b714c45b53653458cc5392685ac60b1e1273e94d.png" width="" height="" 

 /div 

getRandomAsteroid()方法创建了一个随机的位置，然后选择一个随机的大小：small、medium或large。记住，工厂的每一个方法都从3种不同的多边形模型中针对每个大小选取一个模型，并且为每个模型生成4个镜像的版本。每个多边形有4个镜像，每个大小有3个形状，共有3种不同的大小，因此，共有36种不同的模型。

还应该注意，由于PrototypeAsteroid使用了新的Utility.fillPolygon()方法，Graphics对象强制转型为一个Graphics2D对象。

// RandomAsteroidExample.java
protected void render( Graphics g ) {
super.render( g );
g.drawString( "Press ESC to respawn", 20, 35 );
Matrix3x3f view = getViewportTransform();
for( PrototypeAsteroid asteroid : asteroids ) {
asteroid.draw( (Graphics2D)g, view );
}
}
RandomAsteroidExample代码如下所示：

package javagames.prototype;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.util.*;
import javagames.prototype.PrototypeAsteroid.Size;
import javagames.util.*;

public class RandomAsteroidExample extends SimpleFramework {
private PrototypeAsteroidFactory factory;
private ArrayList asteroids;
private Random rand;
public RandomAsteroidExample() {
appBorderScale = 0.9f;
appWidth = 640;
appHeight = 640;
appMaintainRatio = true;
appSleep = 1L;
appTitle = "Random Asteroids";
appBackground = Color.WHITE;
appFPSColor = Color.BLACK;
}
@Override
protected void initialize() {
super.initialize();
rand = new Random();
asteroids = new ArrayList();
PolygonWrapper wrapper =
new PolygonWrapper( appWorldWidth, appWorldHeight );
factory = new PrototypeAsteroidFactory( wrapper );
createAsteroids();
}
private void createAsteroids() {
asteroids.clear();
for( int i = 0; i ++i ) {
asteroids.add( getRandomAsteroid() );
}
}
private PrototypeAsteroid getRandomAsteroid() {
float x = rand.nextFloat() * 2.0f - 1.0f;
float y = rand.nextFloat() * 2.0f - 1.0f;
Vector2f position = new Vector2f( x, y );
Size[] sizes = Size.values();
Size randomSize = sizes[ rand.nextInt( sizes.length ) ];
switch( randomSize ) {
case Small: return factory.createSmallAsteroid( position );
case Medium: return factory.createMediumAsteroid( position );
case Large:
default: return factory.createLargeAsteroid( position );
}
}
@Override
protected void processInput( float delta ) {
super.processInput( delta );
if( keyboard.keyDownOnce( KeyEvent.VK_ESCAPE ) ) {
createAsteroids();
}
}
@Override
protected void updateObjects( float delta ) {
super.updateObjects( delta );
for( PrototypeAsteroid asteroid : asteroids ) {
asteroid.update( delta );
}
}
@Override
protected void render( Graphics g ) {
super.render( g );
g.drawString( "Press ESC to respawn", 20, 35 );
Matrix3x3f view = getViewportTransform();
for( PrototypeAsteroid asteroid : asteroids ) {
asteroid.draw( (Graphics2D)g, view );
}
}
public static void main( String[] args ) {
launchApp( new RandomAsteroidExample() );
}
}`

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