Android游戏开发十日通（4）-行走，跳跃，碰撞检测

经过前面的三篇文章，我们已经对libgdx有了一定的了解，并且搭建了一个简单的游戏场景，下面我们就继续在之前场景上添加更多的元素。

今天要实现的是精灵的行走、跳跃动画，还有碰撞检测。

今天要实现的东西都是基于物理和数学的原理，首先我们来分析一下行走。

游戏中的动画都是帧动画，比如对Bob的行走一步的动画分解：

当这个序列连续播放的时候，就有了行走的效果。

之前已经有了移动的效果，所以只要在移动的时候循环播放动画就可以了。

现在需要的是决定帧的持续时间。

假设游戏渲染的是60FPS， 那么一帧的持续时间就是1/60s = 0.016 s。

对于一个成年人，每分钟大约走180步，那么每秒走的步数就是180/60 = 3，需要播放的帧为3×5 = 15.

那么每一帧持续时间就是1/15 = 0.066s.及66毫秒，即人物在运动的时候只要以66ms/帧对速度播放帧序列，就可以产生行走的效果了。

下面是代码实现。

首先是加载贴图。

和上一篇不同，这里用的是一次性加载贴图的方式，算是对游戏的一种优化。

需要和贴图textures.png一起添加到Android工程的asset/image/textures文件下的还有一个textures.pack文件，类似于一个xml，用于读取序列。

textures.png format: RGBA8888 filter: Nearest,Nearest repeat: none block rotate: false xy: 1, 11 size: 48, 48 orig: 48, 48 offset: 0, 0 index: -1 bob-01 rotate: false xy: 51, 31 size: 24, 28 orig: 24, 28 offset: 0, 0 index: -1 /*..omit..*/

接下来需要修改Bob类。

添加一个statetime成员用于记录Bob生存的时间，后面会用它来决定显示帧序列的哪一帧。

package com.me.testgdxgame.model; import com.badlogic.gdx.math.Rectangle; import com.badlogic.gdx.math.Vector2; public class Bob {	public enum State {	IDLE, WALKING, JUMPING, DYING	}	public static final float SPEED = 4f;	// unit per second	static final float JUMP_VELOCITY = 1f;	public static final float SIZE = 0.5f; // half a unit	Vector2	position = new Vector2();	Vector2	acceleration = new Vector2();	Vector2	velocity = new Vector2();	Rectangle	bounds = new Rectangle();	State	state = State.IDLE;	boolean	facingLeft = true;	float	stateTime = 0;	public Bob(Vector2 position) {	this.position = position;	this.bounds.height = SIZE;	this.bounds.width = SIZE;	}	public boolean isFacingLeft() {	return facingLeft;	}	public void setFacingLeft(boolean facingLeft) {	this.facingLeft = facingLeft;	}	public Vector2 getPosition() {	return position;	}	public Vector2 getAcceleration() {	return acceleration;	}	public Vector2 getVelocity() {	return velocity;	}	public Rectangle getBounds() {	return bounds;	}	public State getState() {	return state;	}	public void setState(State newState) {	this.state = newState;	}	public float getStateTime() {	return stateTime;	}	public void update(float delta) {	stateTime += delta;	position.add(velocity.cpy().mul(delta));	} } 

在libgdx中用于处理这种序列图的工具类是TextureAtlas。

getKeyFrame用于获取动画中的关键帧。

修改WorldRender类。

package com.me.testgdxgame.view; import com.me.testgdxgame.*; import com.me.testgdxgame.model.Block; import com.me.testgdxgame.model.Bob; import com.me.testgdxgame.model.Bob.State; import com.me.testgdxgame.model.World; import com.badlogic.gdx.Gdx; import com.badlogic.gdx.graphics.Color; import com.badlogic.gdx.graphics.GL10; import com.badlogic.gdx.graphics.OrthographicCamera; import com.badlogic.gdx.graphics.Texture; import com.badlogic.gdx.graphics.g2d.Animation; import com.badlogic.gdx.graphics.g2d.SpriteBatch; import com.badlogic.gdx.graphics.g2d.TextureAtlas; import com.badlogic.gdx.graphics.g2d.TextureRegion; import com.badlogic.gdx.graphics.glutils.ShapeRenderer; import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType; import com.badlogic.gdx.math.Rectangle; public class WorldRenderer {	private World world;	private OrthographicCamera cam;	private static final float RUNNING_FRAME_DURATION = 0.06f;	private SpriteBatch spriteBatch;	private boolean debug=false;	private int width;	private int height;	private float ppuX; // pixels per unit on the X axis	private float ppuY; // pixels per unit on the Y axis	private static final float CAMERA_WIDTH = 10f;	private static final float CAMERA_HEIGHT = 7f;	/** Textures **/	private TextureRegion bobIdleLeft;	private TextureRegion bobIdleRight;	private TextureRegion blockTexture;	private TextureRegion bobFrame;	/** Animations **/	private Animation walkLeftAnimation;	private Animation walkRightAnimation;	/** for debug rendering **/	ShapeRenderer debugRenderer = new ShapeRenderer();	public WorldRenderer(World world) {	this.world = world;	this.cam = new OrthographicCamera(10, 7);	this.cam.position.set(5, 3.5f, 0);	this.cam.update();	spriteBatch=new SpriteBatch();	loadTextures();	}	public void setSize (int w, int h) {	this.width = w;	this.height = h;	ppuX = (float)width / CAMERA_WIDTH;	ppuY = (float)height / CAMERA_HEIGHT;	}	private void loadTextures() {	TextureAtlas atlas = new TextureAtlas(Gdx.files.internal("images/textures/textures.pack"));	bobIdleLeft = atlas.findRegion("bob-01");	bobIdleRight = new TextureRegion(bobIdleLeft);	bobIdleRight.flip(true, false);	blockTexture = atlas.findRegion("block");	TextureRegion[] walkLeftFrames = new TextureRegion[5];	for (int i = 0; i < 5; i++) {	walkLeftFrames[i] = atlas.findRegion("bob-0" + (i + 2));	}	walkLeftAnimation = new Animation(RUNNING_FRAME_DURATION, walkLeftFrames);	TextureRegion[] walkRightFrames = new TextureRegion[5];	for (int i = 0; i < 5; i++) {	walkRightFrames[i] = new TextureRegion(walkLeftFrames[i]);	walkRightFrames[i].flip(true, false);	}	walkRightAnimation = new Animation(RUNNING_FRAME_DURATION, walkRightFrames);	}	public void render() {	spriteBatch.begin();	drawBlocks();	drawBob();	spriteBatch.end();	if(debug) drawDebug();	}	private void drawBlocks(){	for (Block block : world.getBlocks()) {	spriteBatch.draw(blockTexture, block.getPosition().x * ppuX, block.getPosition().y * ppuY, Block.SIZE * ppuX, Block.SIZE * ppuY);	}	}	private void drawBob(){	Bob bob = world.getBob(); bobFrame = bob.isFacingLeft() ? bobIdleLeft : bobIdleRight;	//spriteBatch.draw(bobIdleLeft, bob.getPosition().x * ppuX, bob.getPosition().y * ppuY, Bob.SIZE * ppuX, Bob.SIZE * ppuY);	if(bob.getState().equals(State.WALKING)){	bobFrame = bob.isFacingLeft() ? walkLeftAnimation.getKeyFrame(bob.getStateTime(),true):walkRightAnimation.getKeyFrame(bob.getStateTime(),true);	}	spriteBatch.draw(bobFrame, bob.getPosition().x * ppuX, bob.getPosition().y * ppuY, Bob.SIZE * ppuX, Bob.SIZE * ppuY);	}	private void drawDebug(){	// render blocks	debugRenderer.setProjectionMatrix(cam.combined);	debugRenderer.begin(ShapeType.Rectangle);	for (Block block : world.getBlocks()) {	Rectangle rect = block.getBounds();	float x1 = block.getPosition().x + rect.x;	float y1 = block.getPosition().y + rect.y;	debugRenderer.setColor(new Color(1, 0, 0, 1));	debugRenderer.rect(x1, y1, rect.width, rect.height);	}	// render Bob	Bob bob = world.getBob();	Rectangle rect = bob.getBounds();	float x1 = bob.getPosition().x + rect.x;	float y1 = bob.getPosition().y + rect.y;	debugRenderer.setColor(new Color(0, 1, 0, 1));	debugRenderer.rect(x1, y1, rect.width, rect.height);	debugRenderer.end();	} } 

跑一下mian.java,键盘左右键就可以控制小人跑了。

首先来复习一下初中的牛顿三定律...

第一定律：倘物体处于静止状态，或呈等速直线运动，只要没外力作用，物体将保持静止状态，或呈等速直线运动之状态。这定律又称为惯性定律。
第二定律：物体的加速度，与所受的净外力成正比。加速度的方向与净外力的方向相同。即 ；其中，是加速度， 是净外力， 是质量。
第三定律：两个物体的相互作用力总是大小相等，方向相反，同时出现或消失。强版第三定律还额外要求两支作用力的方向都处于同一直线。

分析一下Bob的状态。

最初始的时候，Bob处于静止状态，受两个力，一个是重力，一个是地面的支持力，二力平衡。

上图左边是Bob处于起跳状态，此时Bob用力蹬地面，地面给的反作用力大于Bob受的重力，Bob离开地面，起跳。

上图右边是Bob处于空中的状态，只受重力影响。

要用到一个速度计算公式：

v=u+at

u为初速度，a为加速度，t为时间。

下面看具体的代码实现。只需要在WorldController中添加对应的按键事件处理就可以了。

添加一些静态变量作为世界的参数。修改inputProcess和update函数。

注意仔细分析跳跃处理的逻辑。

package com.me.testgdxgame.controller; import java.util.HashMap; import java.util.Map; import com.me.testgdxgame.model.Bob; import com.me.testgdxgame.model.Bob.State; import com.me.testgdxgame.model.World; public class WorldController {	enum Keys{	LEFT,RIGHT,JUMP,FIRE	}	private World world;	private Bob bob;	private long jumpPressedTime;	private boolean jumpingPressed;	static Map<Keys,Boolean> keys = new HashMap<WorldController.Keys,Boolean>();	static {	keys.put(Keys.LEFT, false);	keys.put(Keys.RIGHT, false);	keys.put(Keys.JUMP, false);	keys.put(Keys.FIRE, false);	};	private static final long LONG_JUMP_PRESS = 150l;	private static final float ACCELERATION = 20f;	private static final float GRAVITY = -20f;	private static final float MAX_JUMP_SPEED = 7f;	private static final float DAMP = 0.8f;	private static final float MAX_VEL = 4f;	private static final float WIDTH =10f;	public WorldController(World w){	world=w;	bob=world.getBob();	}	//Key presses and touches	public void leftPressed(){	keys.get(keys.put(Keys.LEFT, true));	}	public void rightPressed() {	keys.get(keys.put(Keys.RIGHT, true));	}	public void jumpPressed() {	keys.get(keys.put(Keys.JUMP, true));	}	public void firePressed() {	keys.get(keys.put(Keys.FIRE, false));	}	public void leftReleased() {	keys.get(keys.put(Keys.LEFT, false));	}	public void rightReleased() {	keys.get(keys.put(Keys.RIGHT, false));	}	public void jumpReleased() {	keys.get(keys.put(Keys.JUMP, false));	jumpingPressed = false;	}	public void fireReleased() {	keys.get(keys.put(Keys.FIRE, false));	}	public void update(float delta){	processInput();	bob.getAcceleration().y = GRAVITY;	bob.getAcceleration().mul(delta);	bob.getVelocity().add(bob.getAcceleration().x, bob.getAcceleration().y);	if (bob.getAcceleration().x == 0) bob.getVelocity().x *= DAMP;	if (bob.getVelocity().x > MAX_VEL) {	bob.getVelocity().x = MAX_VEL;	}	if (bob.getVelocity().x < -MAX_VEL) {	bob.getVelocity().x = -MAX_VEL;	}	bob.update(delta);	//Set Bob's state to State.IDLE when Bob touch edge	if (bob.getPosition().y < 0) {	bob.getPosition().y = 0f;	bob.setPosition(bob.getPosition());	if (bob.getState().equals(State.JUMPING)) {	bob.setState(State.IDLE);	}	}	if (bob.getPosition().x < 0) {	bob.getPosition().x = 0;	bob.setPosition(bob.getPosition());	if (!bob.getState().equals(State.JUMPING)) {	bob.setState(State.IDLE);	}	}	if (bob.getPosition().x > WIDTH - bob.getBounds().width ) {	bob.getPosition().x = WIDTH - bob.getBounds().width;	bob.setPosition(bob.getPosition());	if (!bob.getState().equals(State.JUMPING)) {	bob.setState(State.IDLE);	}	}	}	private boolean processInput(){	if (keys.get(Keys.JUMP)) {	if (!bob.getState().equals(State.JUMPING)) {	jumpingPressed = true;	jumpPressedTime = System.currentTimeMillis();	bob.setState(State.JUMPING);	bob.getVelocity().y = MAX_JUMP_SPEED;	} else {	if (jumpingPressed && ((System.currentTimeMillis() - jumpPressedTime) >= LONG_JUMP_PRESS)) {	jumpingPressed = false;	} else {	if (jumpingPressed) {	bob.getVelocity().y = MAX_JUMP_SPEED;	}	}	}	}	if(keys.get(Keys.LEFT)){	bob.setFacingLeft(true);	if(!bob.getState().equals(State.JUMPING)){	bob.setState(State.WALKING);	}	bob.getVelocity().x=-ACCELERATION;	}else if (keys.get(Keys.RIGHT)) {	// left is pressed	bob.setFacingLeft(false);	if(!bob.getState().equals(State.JUMPING)){	bob.setState(State.WALKING);	}	bob.getVelocity().x=ACCELERATION;	}else {	if(!bob.getState().equals(State.JUMPING)){	bob.setState(State.IDLE);	}	;	// acceleration is 0 on the x	bob.getAcceleration().x = 0;	}	return false;	} } 

在WorldRender中还需要添加与跳跃对应的纹理还有修改drawBob函数。

加载纹理：

private void loadTextures() {	TextureAtlas atlas = new TextureAtlas(Gdx.files.internal("images/textures/textures.pack"));	bobJumpLeft = atlas.findRegion("bob-up");	bobJumpRight = new TextureRegion(bobJumpLeft);	bobJumpRight.flip(true, false);	bobFallLeft=atlas.findRegion("bob-down");	bobFallRight = new TextureRegion(bobFallLeft);	bobFallRight.flip(true, false);	bobIdleLeft = atlas.findRegion("bob-01");	bobIdleRight = new TextureRegion(bobIdleLeft);	bobIdleRight.flip(true, false);	blockTexture = atlas.findRegion("block");	TextureRegion[] walkLeftFrames = new TextureRegion[5];	for (int i = 0; i < 5; i++) {	walkLeftFrames[i] = atlas.findRegion("bob-0" + (i + 2));	}	walkLeftAnimation = new Animation(RUNNING_FRAME_DURATION, walkLeftFrames);	TextureRegion[] walkRightFrames = new TextureRegion[5];	for (int i = 0; i < 5; i++) {	walkRightFrames[i] = new TextureRegion(walkLeftFrames[i]);	walkRightFrames[i].flip(true, false);	}	walkRightAnimation = new Animation(RUNNING_FRAME_DURATION, walkRightFrames);	}

drawBob函数

private void drawBob(){	Bob bob = world.getBob(); bobFrame = bob.isFacingLeft() ? bobIdleLeft : bobIdleRight; if(bob.getState().equals(State.WALKING)) {	bobFrame = bob.isFacingLeft() ? walkLeftAnimation.getKeyFrame(bob.getStateTime(), true) : walkRightAnimation.getKeyFrame(bob.getStateTime(), true);	} else if (bob.getState().equals(State.JUMPING)) {	if (bob.getVelocity().y > 0) {	bobFrame = bob.isFacingLeft() ? bobJumpLeft : bobJumpRight;	} else {	bobFrame = bob.isFacingLeft() ? bobFallLeft : bobFallRight;	}	}	spriteBatch.draw(bobFrame, bob.getPosition().x * ppuX, bob.getPosition().y * ppuY, Bob.SIZE * ppuX, Bob.SIZE * ppuY);	}

运行一下：

现在的demo是可以穿墙的-_-!,这里的碰撞检测指的是Bob与Blocks之间的碰撞，当Bob撞墙的时候，Bob需要停止前进跳跃或是落下。

最简单的方法就是每update一次就检测Bob与每一个Block是否相撞，当然效率会非常低。

仔细来分析一下：每次与Bob可能发生碰撞的Block只有Bob身边的8块砖，那么在每次Update的时候与检测是否与身边的砖块相碰就可以了。

还可以再简单么？

看下面的图片。

假设Bob正在向右行走，那么在可能与Bob产生碰撞的Block中，只有下面的那个。所以，根据Bob当前的状态进行碰撞检测可以高效地进行碰撞检测。

我们用一个二维数组来保存地形，用于碰撞检测。

首先我们创建一个level，就是关卡，用world来装载，而不是直接在world里面生成。

package com.me.testgdxgame.model; import com.badlogic.gdx.math.Vector2; public class Level {	private int width;	private int height;	private Block[][] blocks;	public int getWidth() {	return width;	}	public void setWidth(int width) {	this.width = width;	}	public int getHeight() {	return height;	}	public void setHeight(int height) {	this.height = height;	}	public Block[][] getBlocks() {	return blocks;	}	public void setBlocks(Block[][] blocks) {	this.blocks = blocks;	}	public Level() {	loadDemoLevel();	}	public Block get(int x, int y) {	return blocks[x][y];	}	private void loadDemoLevel() {	width = 10;	height = 7;	blocks = new Block[width][height];	for (int col = 0; col < width; col++) {	for (int row = 0; row < height; row++) {	blocks[col][row] = null;	}	}	for (int col = 0; col < 10; col++) {	blocks[col][0] = new Block(new Vector2(col, 0));	blocks[col][6] = new Block(new Vector2(col, 6));	if (col > 2) {	blocks[col][1] = new Block(new Vector2(col, 1));	}	}	blocks[9][2] = new Block(new Vector2(9, 2));	blocks[9][3] = new Block(new Vector2(9, 3));	blocks[9][4] = new Block(new Vector2(9, 4));	blocks[9][5] = new Block(new Vector2(9, 5));	blocks[6][3] = new Block(new Vector2(6, 3));	blocks[6][4] = new Block(new Vector2(6, 4));	blocks[6][5] = new Block(new Vector2(6, 5));	} } 

World类做对应的修改：

package com.me.testgdxgame.model; import java.util.ArrayList; import java.util.List; import com.badlogic.gdx.math.Rectangle; import com.badlogic.gdx.math.Vector2; import com.badlogic.gdx.utils.Array; public class World {	/** Our player controlled hero **/	Bob bob;	/** A world has a level through which Bob needs to go through **/	Level level;	/** The collision boxes **/	Array<Rectangle> collisionRects = new Array<Rectangle>();	// Getters -----------	public Array<Rectangle> getCollisionRects() {	return collisionRects;	}	public Bob getBob() {	return bob;	}	public Level getLevel() {	return level;	}	/** Return only the blocks that need to be drawn **/	public List<Block> getDrawableBlocks(int width, int height) {	int x = (int)bob.getPosition().x - width;	int y = (int)bob.getPosition().y - height;	if (x < 0) {	x = 0;	}	if (y < 0) {	y = 0;	}	int x2 = x + 2 * width;	int y2 = y + 2 * height;	if (x2 > level.getWidth()) {	x2 = level.getWidth() - 1;	}	if (y2 > level.getHeight()) {	y2 = level.getHeight() - 1;	}	List<Block> blocks = new ArrayList<Block>();	Block block;	for (int col = x; col <= x2; col++) {	for (int row = y; row <= y2; row++) {	block = level.getBlocks()[col][row];	if (block != null) {	blocks.add(block);	}	}	}	return blocks;	}	// --------------------	public World() {	createDemoWorld();	}	private void createDemoWorld() {	bob = new Bob(new Vector2(7, 2));	level = new Level();	} } 

然后在WorldController中添加一个checkCollisionWithBlocks函数，函数里面首先检测X方向是否有碰撞，再检测Y方向是否有碰撞。

在update函数中，每运行一次就进行一次检测。

完整的WorldController类如下：

package com.me.testgdxgame.controller; import java.util.HashMap; import java.util.Map; import com.badlogic.gdx.math.Rectangle; import com.badlogic.gdx.utils.Array; import com.badlogic.gdx.utils.Pool; import com.me.testgdxgame.model.Block; import com.me.testgdxgame.model.Bob; import com.me.testgdxgame.model.Bob.State; import com.me.testgdxgame.model.World; public class WorldController {	enum Keys {	LEFT, RIGHT, JUMP, FIRE	}	private static final long LONG_JUMP_PRESS	= 150l;	private static final float ACCELERATION	= 20f;	private static final float GRAVITY	= -20f;	private static final float MAX_JUMP_SPEED	= 7f;	private static final float DAMP	= 0.90f;	private static final float MAX_VEL	= 4f;	private World	world;	private Bob	bob;	private long	jumpPressedTime;	private boolean jumpingPressed;	private boolean grounded = false;	// This is the rectangle pool used in collision detection	// Good to avoid instantiation each frame	private Pool<Rectangle> rectPool = new Pool<Rectangle>() {	@Override	protected Rectangle newObject() {	return new Rectangle();	}	};	static Map<Keys, Boolean> keys = new HashMap<WorldController.Keys, Boolean>();	static {	keys.put(Keys.LEFT, false);	keys.put(Keys.RIGHT, false);	keys.put(Keys.JUMP, false);	keys.put(Keys.FIRE, false);	};	// Blocks that Bob can collide with any given frame	private Array<Block> collidable = new Array<Block>();	public WorldController(World world) {	this.world = world;	this.bob = world.getBob();	}	// ** Key presses and touches **************** //	public void leftPressed() {	keys.get(keys.put(Keys.LEFT, true));	}	public void rightPressed() {	keys.get(keys.put(Keys.RIGHT, true));	}	public void jumpPressed() {	keys.get(keys.put(Keys.JUMP, true));	}	public void firePressed() {	keys.get(keys.put(Keys.FIRE, false));	}	public void leftReleased() {	keys.get(keys.put(Keys.LEFT, false));	}	public void rightReleased() {	keys.get(keys.put(Keys.RIGHT, false));	}	public void jumpReleased() {	keys.get(keys.put(Keys.JUMP, false));	jumpingPressed = false;	}	public void fireReleased() {	keys.get(keys.put(Keys.FIRE, false));	}	/** The main update method **/	public void update(float delta) {	// Processing the input - setting the states of Bob	processInput();	// If Bob is grounded then reset the state to IDLE	if (grounded && bob.getState().equals(State.JUMPING)) {	bob.setState(State.IDLE);	}	// Setting initial vertical acceleration	bob.getAcceleration().y = GRAVITY;	// Convert acceleration to frame time	bob.getAcceleration().mul(delta);	// apply acceleration to change velocity	bob.getVelocity().add(bob.getAcceleration().x, bob.getAcceleration().y);	// checking collisions with the surrounding blocks depending on Bob's velocity	checkCollisionWithBlocks(delta);	// apply damping to halt Bob nicely	bob.getVelocity().x *= DAMP;	// ensure terminal velocity is not exceeded	if (bob.getVelocity().x > MAX_VEL) {	bob.getVelocity().x = MAX_VEL;	}	if (bob.getVelocity().x < -MAX_VEL) {	bob.getVelocity().x = -MAX_VEL;	}	// simply updates the state time	bob.update(delta);	}	/** Collision checking **/	private void checkCollisionWithBlocks(float delta) {	// scale velocity to frame units	bob.getVelocity().mul(delta);	// Obtain the rectangle from the pool instead of instantiating it	Rectangle bobRect = rectPool.obtain();	// set the rectangle to bob's bounding box	bobRect.set(bob.getBounds().x, bob.getBounds().y, bob.getBounds().width, bob.getBounds().height);	// we first check the movement on the horizontal X axis	int startX, endX;	int startY = (int) bob.getBounds().y;	int endY = (int) (bob.getBounds().y + bob.getBounds().height);	// if Bob is heading left then we check if he collides with the block on his left	// we check the block on his right otherwise	if (bob.getVelocity().x < 0) {	startX = endX = (int) Math.floor(bob.getBounds().x + bob.getVelocity().x);	} else {	startX = endX = (int) Math.floor(bob.getBounds().x + bob.getBounds().width + bob.getVelocity().x);	}	// get the block(s) bob can collide with	populateCollidableBlocks(startX, startY, endX, endY);	// simulate bob's movement on the X	bobRect.x += bob.getVelocity().x;	// clear collision boxes in world	world.getCollisionRects().clear();	// if bob collides, make his horizontal velocity 0	for (Block block : collidable) {	if (block == null) continue;	if (bobRect.overlaps(block.getBounds())) {	bob.getVelocity().x = 0;	world.getCollisionRects().add(block.getBounds());	break;	}	}	// reset the x position of the collision box	bobRect.x = bob.getPosition().x;	// the same thing but on the vertical Y axis	startX = (int) bob.getBounds().x;	endX = (int) (bob.getBounds().x + bob.getBounds().width);	if (bob.getVelocity().y < 0) {	startY = endY = (int) Math.floor(bob.getBounds().y + bob.getVelocity().y);	} else {	startY = endY = (int) Math.floor(bob.getBounds().y + bob.getBounds().height + bob.getVelocity().y);	}	populateCollidableBlocks(startX, startY, endX, endY);	bobRect.y += bob.getVelocity().y;	for (Block block : collidable) {	if (block == null) continue;	if (bobRect.overlaps(block.getBounds())) {	if (bob.getVelocity().y < 0) {	grounded = true;	}	bob.getVelocity().y = 0;	world.getCollisionRects().add(block.getBounds());	break;	}	}	// reset the collision box's position on Y	bobRect.y = bob.getPosition().y;	// update Bob's position	bob.getPosition().add(bob.getVelocity());	bob.getBounds().x = bob.getPosition().x;	bob.getBounds().y = bob.getPosition().y;	// un-scale velocity (not in frame time)	bob.getVelocity().mul(1 / delta);	}	/** populate the collidable array with the blocks found in the enclosing coordinates **/	private void populateCollidableBlocks(int startX, int startY, int endX, int endY) {	collidable.clear();	for (int x = startX; x <= endX; x++) {	for (int y = startY; y <= endY; y++) {	if (x >= 0 && x < world.getLevel().getWidth() && y >=0 && y < world.getLevel().getHeight()) {	collidable.add(world.getLevel().get(x, y));	}	}	}	}	/** Change Bob's state and parameters based on input controls **/	private boolean processInput() {	if (keys.get(Keys.JUMP)) {	if (!bob.getState().equals(State.JUMPING)) {	jumpingPressed = true;	jumpPressedTime = System.currentTimeMillis();	bob.setState(State.JUMPING);	bob.getVelocity().y = MAX_JUMP_SPEED;	grounded = false;	} else {	if (jumpingPressed && ((System.currentTimeMillis() - jumpPressedTime) >= LONG_JUMP_PRESS)) {	jumpingPressed = false;	} else {	if (jumpingPressed) {	bob.getVelocity().y = MAX_JUMP_SPEED;	}	}	}	}	if (keys.get(Keys.LEFT)) {	// left is pressed	bob.setFacingLeft(true);	if (!bob.getState().equals(State.JUMPING)) {	bob.setState(State.WALKING);	}	bob.getAcceleration().x = -ACCELERATION;	} else if (keys.get(Keys.RIGHT)) {	// left is pressed	bob.setFacingLeft(false);	if (!bob.getState().equals(State.JUMPING)) {	bob.setState(State.WALKING);	}	bob.getAcceleration().x = ACCELERATION;	} else {	if (!bob.getState().equals(State.JUMPING)) {	bob.setState(State.IDLE);	}	bob.getAcceleration().x = 0;	}	return false;	} } 

运行截图：

这篇blog的内容有点多，需要多花时间去体会。

特别是碰撞检测，思路一定要缕清晰。

这个游戏也暂时告一段落了，主要原因是国外的那位大牛也没有更新此系列的文章了...

当然，游戏还在继续。

工程下载

参考：Getting Started in Android Game Development with libgdx-http://obviam.net/