libGDX screen game 多界面游戏

Screen接口

screens对大多数的游戏都是必要的。screens包括了你使用过的ApplicationListener中的一些方法，还包括了一对新的方法：show和hide,前者在Screen获得焦点的时候被调用，后者在Screen失去焦点的时候被调用。

Game类

Game是一个抽象类,它实现了ApplicationListener接口，还有一些帮助设置和处理屏幕渲染的方法。

Screen和Game这两个对象经常被一起使用来构建一个游戏的完整结构。

下面先来看看一个Game类的代码：

package com.badlogic.drop;import com.badlogic.gdx.Game;import com.badlogic.gdx.graphics.g2d.BitmapFont;import com.badlogic.gdx.graphics.g2d.SpriteBatch;public class Drop extends Game {    public SpriteBatch batch;    public BitmapFont font;    public void create() {        batch = new SpriteBatch();        //Use LibGDX's default Arial font.        font = new BitmapFont();        this.setScreen(new MainMenuScreen(this));    }    public void render() {        super.render(); //important!    }    public void dispose() {        batch.dispose();        font.dispose();    }}

我们在程序开始的时候实例化了一个SpriteBatch和一个BitmapFont。创建多个可以被重用的对象是不好的。SpriteBatch对象是用来在屏幕上进行绘制的；BitmapFont使用的时候需要一个SpriteBatch来向屏幕上绘制文字。

下一步，我们设置了Game的当前Screen为MainMenuScreen对象。

一个经常犯的错误就是忘记调用super.render()。如果没有调用这个方法，你设置的这个screen就不会被渲染。

主菜单 Menu Screen

下面，让我们来看看MainMenuScreen类的细节：

package com.badlogic.drop;import com.badlogic.gdx.Gdx;import com.badlogic.gdx.Screen;import com.badlogic.gdx.graphics.GL20;import com.badlogic.gdx.graphics.OrthographicCamera;public class MainMenuScreen implements Screen {    final Drop game;    OrthographicCamera camera;    public MainMenuScreen(final Drop gam) {        game = gam;        camera = new OrthographicCamera();        camera.setToOrtho(false, 800, 480);    }        //...Rest of class omitted for succinctness.}

在上面的代码片段中，我们创建了这个类的构造器,这个类实现了Screen接口。Screen接口并没有提供create()函数，所以我们用一个构造函数来代替。这个构造器的唯一的参数是一个当前游戏的实例（即Drop），所以我们可以访问它的方法和变量。

下一步，MainMenuScreen类中的render(float)方法：

public class MainMenuScreen implements Screen {        //public MainMenuScreen(final Drop gam)....            @Override    public void render(float delta) {        Gdx.gl.glClearColor(0, 0, 0.2f, 1);        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);        camera.update();        game.batch.setProjectionMatrix(camera.combined);        game.batch.begin();        game.font.draw(game.batch, "Welcome to Drop!!! ", 100, 150);        game.font.draw(game.batch, "Tap anywhere to begin!", 100, 100);        game.batch.end();        if (Gdx.input.isTouched()) {            game.setScreen(new GameScreen(game));            dispose();        }    }        //Rest of class still omitted...}

这里的代码是相当健壮的，除了我们需要调用game的SpriteBatch和BitmapFont实例，而不是创建我们自己的。game.font.draw(SpriteBatch,String,float,float)，这个指定了如何在屏幕上进行文字的绘制。

然后，我们检测了屏幕是否被触摸，如果是，那么我们使用setScreen方法把Game的Screen设置成GameScreen，然后释放了当前screen的资源。

游戏界面 Game Screen

这里面的代码几乎和上篇博客中的Drop中的代码一致：

package com.badlogic.drop;import java.util.Iterator;import com.badlogic.gdx.Gdx;import com.badlogic.gdx.Input.Keys;import com.badlogic.gdx.Screen;import com.badlogic.gdx.audio.Music;import com.badlogic.gdx.audio.Sound;import com.badlogic.gdx.graphics.GL20;import com.badlogic.gdx.graphics.OrthographicCamera;import com.badlogic.gdx.graphics.Texture;import com.badlogic.gdx.math.MathUtils;import com.badlogic.gdx.math.Rectangle;import com.badlogic.gdx.math.Vector3;import com.badlogic.gdx.utils.Array;import com.badlogic.gdx.utils.TimeUtils;public class GameScreen implements Screen {    final Drop game;    Texture dropImage;    Texture bucketImage;    Sound dropSound;    Music rainMusic;    OrthographicCamera camera;    Rectangle bucket;    Array<Rectangle> raindrops;    long lastDropTime;    int dropsGathered;    public GameScreen(final Drop gam) {        this.game = gam;        // load the images for the droplet and the bucket, 64x64 pixels each        dropImage = new Texture(Gdx.files.internal("droplet.png"));        bucketImage = new Texture(Gdx.files.internal("bucket.png"));        // load the drop sound effect and the rain background "music"        dropSound = Gdx.audio.newSound(Gdx.files.internal("drop.wav"));        rainMusic = Gdx.audio.newMusic(Gdx.files.internal("rain.mp3"));        rainMusic.setLooping(true);        // create the camera and the SpriteBatch        camera = new OrthographicCamera();        camera.setToOrtho(false, 800, 480);        // create a Rectangle to logically represent the bucket        bucket = new Rectangle();        bucket.x = 800 / 2 - 64 / 2; // center the bucket horizontally        bucket.y = 20; // bottom left corner of the bucket is 20 pixels above                        // the bottom screen edge        bucket.width = 64;        bucket.height = 64;        // create the raindrops array and spawn the first raindrop        raindrops = new Array<Rectangle>();        spawnRaindrop();    }    private void spawnRaindrop() {        Rectangle raindrop = new Rectangle();        raindrop.x = MathUtils.random(0, 800 - 64);        raindrop.y = 480;        raindrop.width = 64;        raindrop.height = 64;        raindrops.add(raindrop);        lastDropTime = TimeUtils.nanoTime();    }    @Override    public void render(float delta) {        // clear the screen with a dark blue color. The        // arguments to glClearColor are the red, green        // blue and alpha component in the range [0,1]        // of the color to be used to clear the screen.        Gdx.gl.glClearColor(0, 0, 0.2f, 1);        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);        // tell the camera to update its matrices.        camera.update();        // tell the SpriteBatch to render in the        // coordinate system specified by the camera.        game.batch.setProjectionMatrix(camera.combined);        // begin a new batch and draw the bucket and        // all drops        game.batch.begin();        game.font.draw(game.batch, "Drops Collected: " + dropsGathered, 0, 480);        game.batch.draw(bucketImage, bucket.x, bucket.y);        for (Rectangle raindrop : raindrops) {            game.batch.draw(dropImage, raindrop.x, raindrop.y);        }        game.batch.end();        // process user input        if (Gdx.input.isTouched()) {            Vector3 touchPos = new Vector3();            touchPos.set(Gdx.input.getX(), Gdx.input.getY(), 0);            camera.unproject(touchPos);            bucket.x = touchPos.x - 64 / 2;        }        if (Gdx.input.isKeyPressed(Keys.LEFT))            bucket.x -= 200 * Gdx.graphics.getDeltaTime();        if (Gdx.input.isKeyPressed(Keys.RIGHT))            bucket.x += 200 * Gdx.graphics.getDeltaTime();        // make sure the bucket stays within the screen bounds        if (bucket.x < 0)            bucket.x = 0;        if (bucket.x > 800 - 64)            bucket.x = 800 - 64;        // check if we need to create a new raindrop        if (TimeUtils.nanoTime() - lastDropTime > 1000000000)            spawnRaindrop();        // move the raindrops, remove any that are beneath the bottom edge of        // the screen or that hit the bucket. In the later case we increase the         // value our drops counter and add a sound effect.        Iterator<Rectangle> iter = raindrops.iterator();        while (iter.hasNext()) {            Rectangle raindrop = iter.next();            raindrop.y -= 200 * Gdx.graphics.getDeltaTime();            if (raindrop.y + 64 < 0)                iter.remove();            if (raindrop.overlaps(bucket)) {                dropsGathered++;                dropSound.play();                iter.remove();            }        }    }    @Override    public void resize(int width, int height) {    }    @Override    public void show() {        // start the playback of the background music        // when the screen is shown        rainMusic.play();    }    @Override    public void hide() {    }    @Override    public void pause() {    }    @Override    public void resume() {    }    @Override    public void dispose() {        dropImage.dispose();        bucketImage.dispose();        dropSound.dispose();        rainMusic.dispose();    }}

上面的代码和Drop几乎一致，只不过我们使用构造器来代替了create()方法。

上面的代码中也在左上角添加了一个字符串，用来跟踪有多少个雨滴被收集到了。

上面就是你所要知道的关于Game和Screen的知识，这样就可以来构建一个拥有多界面的游戏了。