1 前言

        libGDX 是一个开源且跨平台的 Java 游戏开发框架，于 2010 年 3 月 11 日推出 0.1 版本，它通过 OpenGL ES 2.0/3.0 渲染图像，支持 Windows、Linux、macOS、Android、iOS、Web 等平台，提供了统一的 API，用户只需要写一套代码就可以在多个平台上运行，官方介绍见 → Features。

        libGDX 相关链接如下：

2 libGDX 环境搭建

        1）下载 gdx-setup

        官方下载链接：gdx-setup.jar，如果网速较慢，用户也可以从这里下载：libGDX全套工具包。

        2）生成项目

        双击 gdx-setup.jar 文件，填写 Project name、Package name、Game Class、Output folder、Android SDK、Supported Platforms 等信息，点击 Generate 生成项目。官方介绍见 → Generate a Project。

        注意：JDK 最低版为 11，见官方说明 → Set Up a Dev Environment。

        3）打开项目

        使用 Android Studio 打开生成的 Drop 项目，等待自动下载依赖，项目结构如下。

        注意：如果选择了 Android 启动，需要在 gradle.properties 文件中添加 AndroidX 支持，如下。

android.useAndroidX=true

        DesktopLauncher.java

package com.zhyan8.drop;

import com.badlogic.gdx.backends.lwjgl3.Lwjgl3Application;
import com.badlogic.gdx.backends.lwjgl3.Lwjgl3ApplicationConfiguration;

public class DesktopLauncher {
	public static void main (String[] arg) {
		Lwjgl3ApplicationConfiguration config = new Lwjgl3ApplicationConfiguration();
		config.setForegroundFPS(60);
		config.setTitle("Drop");
		new Lwjgl3Application(new Drop(), config);
	}
}

        AndroidLauncher.java

package com.zhyan8.drop;

import android.os.Bundle;

import com.badlogic.gdx.backends.android.AndroidApplication;
import com.badlogic.gdx.backends.android.AndroidApplicationConfiguration;

public class AndroidLauncher extends AndroidApplication {
	@Override
	protected void onCreate (Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
		initialize(new Drop(), config);
	}
}

        Drop.java

package com.zhyan8.drop;

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.utils.ScreenUtils;

public class Drop extends ApplicationAdapter {
	SpriteBatch batch;
	Texture img;

	@Override
	public void create () {
		batch = new SpriteBatch();
		img = new Texture("badlogic.jpg");
	}

	@Override
	public void render () {
		ScreenUtils.clear(1, 0, 0, 1);
		batch.begin();
		batch.draw(img, 0, 0);
		batch.end();
	}

	@Override
	public void dispose () {
		batch.dispose();
		img.dispose();
	}
}

        4）运行项目（点击操作）

        Desktop：

        Android：

        运行效果如下。

        5）运行项目（通过命令）

        可以通过在 Terminal 中运行以下命令来运行项目，见官方介绍 → Importing & Running。

        Desktop：

./gradlew desktop:run

        Android：

./gradlew android:installDebug android:run

        iOS：

./gradlew ios:launchIPhoneSimulator

        HTML：

./gradlew html:superDev

3 libGDX 官方案例

        官方接水游戏见 → A Simple Game，本节完整代码资源见 → 基于libGDX实现接水游戏。

        在第二节的基础上，修改 Drop.java，如下。

        Drop.java

package com.zhyan8.drop;

import java.util.Iterator;

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Input.Keys;
import com.badlogic.gdx.audio.Music;
import com.badlogic.gdx.audio.Sound;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
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.ScreenUtils;
import com.badlogic.gdx.utils.TimeUtils;

public class Drop extends ApplicationAdapter {
	private Texture dropImage;
	private Texture bucketImage;
	private Sound dropSound;
	private Music rainMusic;
	private SpriteBatch batch;
	private OrthographicCamera camera;
	private Rectangle bucket;
	private Array<Rectangle> raindrops;
	private long lastDropTime;

	@Override
	public void create() {
		// 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.mp3"));
		rainMusic = Gdx.audio.newMusic(Gdx.files.internal("rain.mp3"));

		// start the playback of the background music immediately
		rainMusic.setLooping(true);
		rainMusic.play();

		// create the camera and the SpriteBatch
		camera = new OrthographicCamera();
		camera.setToOrtho(false, 800, 480);
		batch = new SpriteBatch();

		// 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() {
		// clear the screen with a dark blue color. The
		// arguments to clear are the red, green
		// blue and alpha component in the range [0,1]
		// of the color to be used to clear the screen.
		ScreenUtils.clear(0, 0, 0.2f, 1);

		// tell the camera to update its matrices.
		camera.update();

		// tell the SpriteBatch to render in the
		// coordinate system specified by the camera.
		batch.setProjectionMatrix(camera.combined);

		// begin a new batch and draw the bucket and
		// all drops
		batch.begin();
		batch.draw(bucketImage, bucket.x, bucket.y);
		for(Rectangle raindrop: raindrops) {
			batch.draw(dropImage, raindrop.x, raindrop.y);
		}
		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 latter case we play back
		// a sound effect as well.
		for (Iterator<Rectangle> iter = raindrops.iterator(); iter.hasNext(); ) {
			Rectangle raindrop = iter.next();
			raindrop.y -= 200 * Gdx.graphics.getDeltaTime();
			if(raindrop.y + 64 < 0) iter.remove();
			if(raindrop.overlaps(bucket)) {
				dropSound.play();
				iter.remove();
			}
		}
	}

	@Override
	public void dispose() {
		// dispose of all the native resources
		dropImage.dispose();
		bucketImage.dispose();
		dropSound.dispose();
		rainMusic.dispose();
		batch.dispose();
	}
}

        音频和图片资源放在 assets 目录下面，如下。

        Desktop 运行效果如下：

        Android 运行效果如下：

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