Complete box2d implementation, all collisions handled with box2d

Shield re-implemented as an entity with a box2d body
Multiball powerup now spawns balls at paddle instead of from block location

build.gradle

@@ -46,6 +46,7 @@ project(":desktop") {
         compile project(":core")
         compile "com.badlogicgames.gdx:gdx-backend-lwjgl:$gdxVersion"
         compile "com.badlogicgames.gdx:gdx-platform:$gdxVersion:natives-desktop"
+        compile "com.badlogicgames.gdx:gdx-box2d-platform:$gdxVersion:natives-desktop"
         
     }
 }
@@ -56,7 +57,9 @@ project(":core") {
 
     dependencies {
         compile "com.badlogicgames.gdx:gdx:$gdxVersion"
+        compile "com.badlogicgames.gdx:gdx-box2d:$gdxVersion"
         compile "net.dermetfan.libgdx-utils:libgdx-utils:0.13.4"
+        compile "net.dermetfan.libgdx-utils:libgdx-utils-box2d:0.13.4"
         
     }
 }

core/src/com/me/brickbuster/entity/Ball.java

@@ -6,102 +6,108 @@ import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.MathUtils;
 import com.badlogic.gdx.math.Vector2;
-import com.me.brickbuster.BrickBuster;
+import com.badlogic.gdx.physics.box2d.Body;
-import com.me.brickbuster.Utils;
+import com.badlogic.gdx.physics.box2d.BodyDef;
+import com.badlogic.gdx.physics.box2d.CircleShape;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
+import com.me.brickbuster.physics.CollisionListener;
+import com.me.brickbuster.physics.PhysicsBody;
 import com.me.brickbuster.state.PlayState;
-import net.dermetfan.utils.Pair;
 
-import java.util.Iterator;
+public class Ball extends Entity implements PhysicsBody, CollisionListener {
 
-public class Ball extends Entity {
+	public static final float RADIUS = 1.2f;
-
-	public static final int RADIUS = 45;
 	public static final Color BALL_COLOR = Color.CHARTREUSE;
-	public static final float DEFAULT_SPEED = 1800;
+	public static final float DEFAULT_SPEED = 45;
-	public static final float BOOST_SPEED = 2200;
+	public static final float BOOST_SPEED = 55;
 	public static final int BLOCKS_FOR_BOOST = 39;
 
-	public Vector2 direction;
 	private float speed;
 	private boolean isStuck = true;
-	private boolean isDead = false;
+	private boolean touchedPaddle = false;
+
+	private Body body;
 
 	public Ball(PlayState state) {
-		super(state,BrickBuster.BOARD_WIDTH /2, state.paddle.getY() + Paddle.PADDLE_HEIGHT + RADIUS);
+		super(state, state.paddle.getX(), state.paddle.getY() + Paddle.PADDLE_HEIGHT + RADIUS);
 		this.speed = state.bricks.size() > BLOCKS_FOR_BOOST? DEFAULT_SPEED : BOOST_SPEED;
+		createBody();
 	}
 
 	@Override
 	public void render(ShapeRenderer sr) {
 		sr.begin(ShapeType.Filled);
 		sr.setColor(BALL_COLOR);
-		sr.circle(pos.x, pos.y, RADIUS);
+		sr.circle(pos.x * PlayState.PIXEL_PER_METER,
+				pos.y * PlayState.PIXEL_PER_METER,
+				RADIUS * PlayState.PIXEL_PER_METER);
 		sr.end();
 	}
 
 	@Override
 	public void update(float dt) {
-		if (isStuck || isDead) {
+		if (isStuck || deleted) {
-			if (!isDead && Gdx.input.justTouched()) {
+			if (!deleted && Gdx.input.justTouched()) {
 				launch();
 			} else {
 				return;
 			}
 		}
-
+		if (touchedPaddle) {
-		Vector2 new_pos = pos.cpy().add(direction.cpy().scl(speed * dt));
-
-		boolean brickCollision = false;
-		Iterator<Brick> brickIterator = state.bricks.iterator();
-		while (!brickCollision && brickIterator.hasNext()) {
-			Brick brick = brickIterator.next();
-			Vector2[] vertices = brick.getVertices();
-			for(int i = 0; i < vertices.length; i++) {
-				Vector2 v1 = vertices[i];
-				Vector2 v2 = vertices[i+1 < vertices.length? i+1 : 0];
-				Vector2 segment = v2.cpy().sub(v1);
-				Vector2 nearest = Utils.nearestPoint(v1.cpy(), segment, new_pos.cpy());
-
-				if (nearest.dst(new_pos.x, new_pos.y) <= RADIUS) {
-					if (brick.hit()) {
-						brickIterator.remove();
-					}
-					Utils.reflect(direction, segment.nor());
-					brickCollision = true;
-					break;
-				}
-			}
-		}
-
-		if (new_pos.x + RADIUS > BrickBuster.BOARD_WIDTH || new_pos.x - RADIUS < 0) {
-			Utils.reflect(direction, Utils.VERTICAL_EDGE);
-		} else if (new_pos.y + RADIUS > BrickBuster.BOARD_HEIGHT) {
-			Utils.reflect(direction, Utils.HORIZONTAL_EDGE);
-		} else if (state.getShieldCount() > 0
-					&& new_pos.y - RADIUS < PlayState.SHIELD_HEIGHT * state.getShieldCount()) {
-			Utils.reflect(direction, Utils.HORIZONTAL_EDGE);
-			state.removeShield();
-		} else if (new_pos.y + RADIUS < 0) {
-			isDead = true;
-			return;
-		} else if (direction.y < 0 && new_pos.y <= state.paddle.getY() + Paddle.PADDLE_HEIGHT + RADIUS) {
-			Pair<Vector2, Vector2> paddle = state.paddle.getTopEdge();
-			Vector2 lineDir = paddle.getValue().sub(paddle.getKey());
-			Vector2 nearest = Utils.nearestPoint(paddle.getKey().cpy(), lineDir, new_pos.cpy());
-
-			if (nearest.dst(new_pos.x, new_pos.y) <= RADIUS) {
 			paddleCollision();
-				if (state.paddle.isSticky()) {
+			touchedPaddle = false;
-					return;
 		}
+
+		if (getY() + RADIUS < 0) {
+			deleted = true;
+		}
+
+		body.setLinearVelocity(body.getLinearVelocity().nor().scl(speed));
+	}
+
+	@Override
+	public Body getBody() {
+		return body;
+	}
+
+	@Override
+	public void createBody() {
+		BodyDef ballBody = new BodyDef();
+		ballBody.type = BodyDef.BodyType.DynamicBody;
+		ballBody.position.set(pos);
+
+		CircleShape ballShape = new CircleShape();
+		ballShape.setRadius(RADIUS);
+
+		FixtureDef ballFixture = new FixtureDef();
+		ballFixture.shape = ballShape;
+		ballFixture.restitution = 1f;
+		ballFixture.friction = 0f;
+
+		body = state.world.createBody(ballBody);
+		body.createFixture(ballFixture);
+		body.setUserData(this);
+
+		ballShape.dispose();
+	}
+
+	@Override
+	public void beginContact(Entity contacted) {
+		if (contacted instanceof Shield) {
+			contacted.delete();
+		}
+
+		if (contacted instanceof Paddle && !isStuck) {
+			touchedPaddle = true;
 		}
 	}
 
-		pos.add(direction.cpy().scl(speed * dt));
+	@Override
+	public void endContact(Entity contacted) {
 	}
 
 	public Vector2 paddleReflectAngle() {
-		int trim = (int) (state.paddle.getWidth() * 0.10);
+		float trim = state.paddle.getWidth() * 0.10f;
 		float rel = MathUtils.clamp((pos.x - state.paddle.getX()) + (state.paddle.getWidth()/2),
 				trim, state.paddle.getWidth()-trim);
 		float newAngle = MathUtils.PI - (MathUtils.PI * (rel / state.paddle.getWidth()));
@@ -109,23 +115,43 @@ public class Ball extends Entity {
 	}
 
 	public void launch() {
+		Vector2 direction;
 		if (state.paddle.isSticky()) {
 			direction = paddleReflectAngle();
 		} else {
 			// launch at random angle between 135 and 45 degrees
 			float angle = MathUtils.random(MathUtils.PI/2) + MathUtils.PI/4;
 			direction = new Vector2(MathUtils.cos(angle), MathUtils.sin(angle));
+
 		}
+		body.setLinearVelocity(direction.scl(speed));
 		isStuck = false;
 	}
 
 	public void paddleCollision() {
 		if (state.paddle.isSticky()) {
 			isStuck = true;
-			pos.y = state.paddle.getY() + Paddle.PADDLE_HEIGHT + RADIUS;
+			body.setLinearVelocity(new Vector2());
+			setY(state.paddle.getY() + Paddle.PADDLE_HEIGHT + RADIUS);
 			return;
 		}
-		direction = paddleReflectAngle();
+		body.setLinearVelocity(paddleReflectAngle().scl(speed));
+	}
+
+	@Override
+	public void setX(float x) {
+		super.setX(x);
+		Vector2 bodyPos = body.getPosition();
+		bodyPos.x = x;
+		body.setTransform(bodyPos, 0);
+	}
+
+	@Override
+	public void setY(float y) {
+		super.setY(y);
+		Vector2 bodyPos = body.getPosition();
+		bodyPos.y = y;
+		body.setTransform(bodyPos, 0);
 	}
 
 	public void setSpeed(float speed) {
@@ -136,15 +162,4 @@ public class Ball extends Entity {
 		return isStuck;
 	}
 
-	public boolean isDead() {
-		return isDead;
-	}
-
-	public void setDirection(Vector2 direction) {
-		this.direction = direction;
-	}
-
-	public void setStuck(boolean stuck) {
-		isStuck = stuck;
-	}
 }

core/src/com/me/brickbuster/entity/Brick.java

@@ -4,50 +4,96 @@ import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.Vector2;
+import com.badlogic.gdx.physics.box2d.Body;
+import com.badlogic.gdx.physics.box2d.BodyDef;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
+import com.badlogic.gdx.physics.box2d.PolygonShape;
 import com.me.brickbuster.entity.powerup.PowerUpType;
+import com.me.brickbuster.physics.CollisionListener;
+import com.me.brickbuster.physics.PhysicsBody;
 import com.me.brickbuster.state.PlayState;
 
-public class Brick extends Entity {
+public class Brick extends Entity implements PhysicsBody, CollisionListener {
 
 	public static final Color DEFAULT_COLOR = Color.FOREST;
-	public static final int BRICK_WIDTH = 200;
+	public static final float BRICK_WIDTH = 5f;
-	public static final int BRICK_HEIGHT = 100;
+	public static final float BRICK_HEIGHT = 2.5f;
 
 	private PowerUpType powerUpType;
 	private Color color;
 
-	private Vector2[] vertices;
+	private Body body;
+	private boolean hitByBall = false;
 
-	public Brick(PlayState state, PowerUpType powerUpType, int x, int y) {
+	public Brick(PlayState state, PowerUpType powerUpType, float x, float y) {
 		this(state, powerUpType, true, x, y);
 	}
 
-	public Brick(PlayState state, PowerUpType powerUpType, boolean hidePowerup, int x, int y) {
+	public Brick(PlayState state, PowerUpType powerUpType, boolean hidePowerup, float x, float y) {
 		this(state, powerUpType, DEFAULT_COLOR, hidePowerup, x, y);
 	}
 
-	public Brick(PlayState state, PowerUpType powerUpType, Color color, boolean hidePowerUp, int x, int y) {
+	public Brick(PlayState state, PowerUpType powerUpType, Color color, boolean hidePowerUp, float x, float y) {
 		super(state, x, y);
 		this.powerUpType = powerUpType;
 		this.color = powerUpType != null && !hidePowerUp? powerUpType.getColor() : color;
-		this.vertices = new Vector2[] {
+		createBody();
-			new Vector2(x, y),
-			new Vector2(x + BRICK_WIDTH, y),
-			new Vector2(x + BRICK_WIDTH, y + BRICK_HEIGHT),
-			new Vector2(x, y + BRICK_HEIGHT)
-		};
 	}
 
 	@Override
 	public void render(ShapeRenderer sr) {
 		sr.begin(ShapeType.Filled);
 		sr.setColor(color);
-		sr.rect(getX(), getY(), BRICK_WIDTH, BRICK_HEIGHT);
+		sr.rect(getX() * PlayState.PIXEL_PER_METER,
+				getY() * PlayState.PIXEL_PER_METER,
+				BRICK_WIDTH * PlayState.PIXEL_PER_METER,
+				BRICK_HEIGHT * PlayState.PIXEL_PER_METER);
 		sr.end();
 	}
 
 	@Override
 	public void update(float dt) {
+		if (hitByBall) {
+			hit();
+			hitByBall = false;
+		}
+	}
+
+	@Override
+	public Body getBody() {
+		return body;
+	}
+
+	@Override
+	public void createBody() {
+		BodyDef brickBody = new BodyDef();
+		brickBody.type = BodyDef.BodyType.StaticBody;
+		brickBody.position.set(pos.cpy());
+
+		PolygonShape brickShape = new PolygonShape();
+		brickShape.setAsBox(BRICK_WIDTH/2, BRICK_HEIGHT/2,
+				new Vector2(BRICK_WIDTH/2,BRICK_HEIGHT/2), 0);
+
+		FixtureDef brickFixture = new FixtureDef();
+		brickFixture.shape = brickShape;
+		brickFixture.friction = 0f;
+
+		body = state.world.createBody(brickBody);
+		body.createFixture(brickFixture);
+		body.setUserData(this);
+
+		brickShape.dispose();
+	}
+
+	@Override
+	public void beginContact(Entity contacted) {
+		if (contacted instanceof Ball) {
+			hitByBall = true;
+		}
+	}
+
+	@Override
+	public void endContact(Entity contacted) {
 	}
 
 	public boolean hit() {
@@ -60,11 +106,9 @@ public class Brick extends Entity {
 		if (powerUpType != null) {
 			state.powerUps.add(powerUpType.createInstance(state, this));
 		}
+
+		deleted = true;
 		return true;
 	}
 
-	public Vector2[] getVertices() {
-		return vertices;
-	}
-
 }

core/src/com/me/brickbuster/entity/Entity.java

@@ -8,6 +8,7 @@ public abstract class Entity {
 
 	protected PlayState state;
 	protected Vector2 pos;
+	protected boolean deleted = false;
 
 	public Entity(PlayState state, Vector2 pos) {
 		this(state, pos.x, pos.y);
@@ -46,4 +47,12 @@ public abstract class Entity {
 		pos.y = y;
 	}
 
+	public void delete() {
+		this.deleted = true;
+	}
+
+	public boolean isDeleted() {
+		return deleted;
+	}
+
 }

core/src/com/me/brickbuster/entity/Paddle.java

@@ -6,31 +6,43 @@ import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.Vector2;
-import com.me.brickbuster.BrickBuster;
+import com.badlogic.gdx.physics.box2d.Body;
+import com.badlogic.gdx.physics.box2d.BodyDef;
+import com.badlogic.gdx.physics.box2d.EdgeShape;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
+import com.me.brickbuster.physics.CollisionListener;
+import com.me.brickbuster.physics.PhysicsBody;
 import com.me.brickbuster.state.PlayState;
 import net.dermetfan.utils.Pair;
 
-public class Paddle extends Entity {
+public class Paddle extends Entity implements PhysicsBody {
 
 	public static final Color STICKY_COLOR = Color.GRAY;
 	public static final Color PADDLE_COLOR = Color.BLACK;
-	public static final int DEFAULT_WIDTH = 300;
-	public static final int PADDLE_HEIGHT = 30;
-	public static final int PADDLE_Y = 50;
-	public static final int PADDLE_SPEED = 1500;
 
-	private int width = DEFAULT_WIDTH;
+	public static final float DEFAULT_WIDTH = 7.5f;
+	public static final float PADDLE_HEIGHT = 0.75f;
+	public static final float PADDLE_Y = 1.25f;
+	public static final float PADDLE_SPEED = 40f;
+
+	private float width = DEFAULT_WIDTH;
 	private boolean sticky = false;
 
+	private Body body;
+
 	public Paddle(PlayState brickBuster) {
-		super(brickBuster, BrickBuster.BOARD_WIDTH / 2, PADDLE_Y);
+		super(brickBuster, PlayState.BOARD_WIDTH/2, PADDLE_Y);
+		createBody();
 	}
 
 	@Override
 	public void render(ShapeRenderer sr) {
 		sr.begin(ShapeType.Filled);
 		sr.setColor(sticky? STICKY_COLOR : PADDLE_COLOR);
-		sr.rect(getX() - width/2, getY(), width, PADDLE_HEIGHT);
+		sr.rect((getX() - width/2) * PlayState.PIXEL_PER_METER,
+				getY() * PlayState.PIXEL_PER_METER,
+				width * PlayState.PIXEL_PER_METER,
+				PADDLE_HEIGHT * PlayState.PIXEL_PER_METER);
 		sr.end();
 	}
 
@@ -41,7 +53,7 @@ public class Paddle extends Entity {
 				setX(width/2);
 				return;
 			}
-			pos.x = pos.x - PADDLE_SPEED * dt;
+			setX(pos.x - PADDLE_SPEED * dt);
 
 			for (Ball ball : state.balls) {
 				if (ball.isStuck()) {
@@ -50,11 +62,11 @@ public class Paddle extends Entity {
 			}
 		}
 		if (Gdx.input.isKeyPressed(Input.Keys.RIGHT)) {
-			if (pos.x + width/2 + PADDLE_SPEED * dt > BrickBuster.BOARD_WIDTH) {
+			if (pos.x + width/2 + PADDLE_SPEED * dt > PlayState.BOARD_WIDTH) {
-				setX(BrickBuster.BOARD_WIDTH - width/2);
+				setX(PlayState.BOARD_WIDTH - width/2);
 				return;
 			}
-			pos.x = pos.x + PADDLE_SPEED * dt;
+			setX(pos.x + PADDLE_SPEED * dt);
 
 			for (Ball ball : state.balls) {
 				if (ball.isStuck()) {
@@ -64,19 +76,59 @@ public class Paddle extends Entity {
 		}
 	}
 
-	public Pair<Vector2, Vector2> getTopEdge() {
+	@Override
-		return new Pair<Vector2, Vector2>(
+	public void createBody() {
-				new Vector2(pos.x - width/2, pos.y + PADDLE_HEIGHT),
+		BodyDef paddleBody = new BodyDef();
-				new Vector2(pos.x + width/2, pos.y + PADDLE_HEIGHT)
+		paddleBody.type = BodyDef.BodyType.KinematicBody;
-		);
+		paddleBody.position.set(pos);
+
+		EdgeShape paddleShape = new EdgeShape();
+		paddleShape.set(new Vector2(-width/2, PADDLE_HEIGHT),
+				new Vector2(width/2, PADDLE_HEIGHT));
+
+		FixtureDef paddleFixture = new FixtureDef();
+		paddleFixture.shape = paddleShape;
+		//paddleFixture.isSensor = true;
+
+		body = state.world.createBody(paddleBody);
+		body.createFixture(paddleFixture);
+		body.setUserData(this);
+
+		paddleShape.dispose();
 	}
 
-	public int getWidth() {
+	@Override
+	public Body getBody() {
+		return body;
+	}
+
+	@Override
+	public void setX(float x) {
+		super.setX(x);
+		Vector2 bodyPos = body.getPosition();
+		bodyPos.x = x;
+		body.setTransform(bodyPos, 0);
+	}
+
+	@Override
+	public void setY(float y) {
+		super.setY(y);
+		Vector2 bodyPos = body.getPosition();
+		bodyPos.y = y;
+		body.setTransform(bodyPos, 0);
+	}
+
+	public float getWidth() {
 		return width;
 	}
 
-	public void setWidth(int width) {
+	public void setWidth(float width) {
+		if (this.width == width) {
+			return;
+		}
+		state.world.destroyBody(body);
 		this.width = width;
+		createBody();
 	}
 
 	public boolean isSticky() {

core/src/com/me/brickbuster/entity/Shield.java

@@ -0,0 +1,67 @@
+package com.me.brickbuster.entity;
+
+import com.badlogic.gdx.graphics.Color;
+import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
+import com.badlogic.gdx.math.Vector2;
+import com.badlogic.gdx.physics.box2d.Body;
+import com.badlogic.gdx.physics.box2d.BodyDef;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
+import com.badlogic.gdx.physics.box2d.PolygonShape;
+import com.me.brickbuster.entity.powerup.PowerUpType;
+import com.me.brickbuster.physics.PhysicsBody;
+import com.me.brickbuster.state.PlayState;
+
+public class Shield extends Entity implements PhysicsBody {
+
+	public static final float SHIELD_HEIGHT = 0.75f;
+
+	private Body body;
+
+	public Shield(PlayState state) {
+		super(state, 0, state.getShieldCount() * SHIELD_HEIGHT);
+		createBody();
+	}
+
+	@Override
+	public void render(ShapeRenderer sr) {
+		sr.begin(ShapeRenderer.ShapeType.Filled);
+		sr.setColor(PowerUpType.SHIELD.getColor());
+		sr.rect(0, pos.y * PlayState.PIXEL_PER_METER,
+				PlayState.BOARD_WIDTH * PlayState.PIXEL_PER_METER,
+				SHIELD_HEIGHT * PlayState.PIXEL_PER_METER);
+		sr.end();
+	}
+
+	@Override
+	public void update(float dt) {
+		if (deleted) {
+			state.removeShield(this);
+		}
+	}
+
+	@Override
+	public void createBody() {
+		BodyDef brickBody = new BodyDef();
+		brickBody.type = BodyDef.BodyType.StaticBody;
+		brickBody.position.set(pos.cpy());
+
+		PolygonShape brickShape = new PolygonShape();
+		brickShape.setAsBox(PlayState.BOARD_WIDTH/2, SHIELD_HEIGHT/2,
+				new Vector2(PlayState.BOARD_WIDTH/2,SHIELD_HEIGHT/2), 0);
+
+		FixtureDef brickFixture = new FixtureDef();
+		brickFixture.shape = brickShape;
+		brickFixture.friction = 0f;
+
+		body = state.world.createBody(brickBody);
+		body.createFixture(brickFixture);
+		body.setUserData(this);
+
+		brickShape.dispose();
+	}
+
+	@Override
+	public Body getBody() {
+		return body;
+	}
+}

core/src/com/me/brickbuster/entity/powerup/MultiBallPowerUp.java

@@ -4,6 +4,7 @@ import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.math.MathUtils;
 import com.badlogic.gdx.math.Vector2;
 import com.me.brickbuster.entity.Ball;
+import com.me.brickbuster.entity.Paddle;
 import com.me.brickbuster.state.PlayState;
 
 public class MultiBallPowerUp extends PowerUp {
@@ -19,10 +20,7 @@ public class MultiBallPowerUp extends PowerUp {
 	public void activate() {
 		for (int x = 0; x < 2; x++) {
 			Ball ball = new Ball(state);
-			ball.setPos(pos.cpy());
+			ball.launch();
-			float angle = MathUtils.random(MathUtils.PI*2);
-			ball.setDirection(new Vector2(MathUtils.cos(angle), MathUtils.sin(angle)));
-			ball.setStuck(false);
 			state.balls.add(ball);
 		}
 	}

core/src/com/me/brickbuster/entity/powerup/PowerUp.java

@@ -4,53 +4,93 @@ import com.badlogic.gdx.graphics.Color;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
 import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.Vector2;
+import com.badlogic.gdx.physics.box2d.Body;
+import com.badlogic.gdx.physics.box2d.BodyDef;
+import com.badlogic.gdx.physics.box2d.CircleShape;
+import com.badlogic.gdx.physics.box2d.FixtureDef;
 import com.me.brickbuster.Utils;
 import com.me.brickbuster.entity.Entity;
+import com.me.brickbuster.entity.Paddle;
+import com.me.brickbuster.physics.CollisionListener;
+import com.me.brickbuster.physics.PhysicsBody;
 import com.me.brickbuster.state.PlayState;
 import net.dermetfan.utils.Pair;
 
-public abstract class PowerUp extends Entity {
+public abstract class PowerUp extends Entity implements PhysicsBody, CollisionListener {
 
-	public static final int RADIUS = 45;
+	public static final float RADIUS = 1.2f;
-	public static final int FALL_SPEED = 600;
+	public static final float FALL_SPEED = 15f;
 
 	private Color color;
 	private boolean isCaught;
 
+	private Body body;
+
 	public PowerUp(PlayState state, Vector2 pos, Color color) {
 		super(state, pos);
 		this.color = color;
+		createBody();
 	}
 
 	@Override
 	public void render(ShapeRenderer sr) {
 		sr.begin(ShapeType.Filled);
 		sr.setColor(color);
-		sr.circle(getX(), getY(), RADIUS);
+		sr.circle(getX() * PlayState.PIXEL_PER_METER,
+				getY() * PlayState.PIXEL_PER_METER,
+				RADIUS * PlayState.PIXEL_PER_METER);
 		sr.end();
 	}
 
 	@Override
 	public void update(float dt) {
-		setY(getY() - FALL_SPEED * dt);
+		if (isCaught) {
-
-		Pair<Vector2, Vector2> paddle = state.paddle.getTopEdge();
-		Vector2 lineDir = paddle.getValue().sub(paddle.getKey());
-		Vector2 nearest = Utils.nearestPoint(paddle.getKey().cpy(), lineDir, getPos().cpy());
-
-		if (nearest.dst(getX(), getY()) <= RADIUS) {
 			activate();
-			isCaught = true;
+			delete();
 		}
 
 		if (getY() + RADIUS < 0) {
+			delete();
+		}
+	}
+
+	@Override
+	public Body getBody() {
+		return body;
+	}
+
+	@Override
+	public void createBody() {
+		BodyDef ballBody = new BodyDef();
+		ballBody.type = BodyDef.BodyType.DynamicBody;
+		ballBody.position.set(pos);
+
+		CircleShape ballShape = new CircleShape();
+		ballShape.setRadius(RADIUS);
+
+		FixtureDef ballFixture = new FixtureDef();
+		ballFixture.shape = ballShape;
+		ballFixture.isSensor = true;
+
+		body = state.world.createBody(ballBody);
+		body.createFixture(ballFixture);
+		body.setUserData(this);
+
+		body.setLinearVelocity(0f, -FALL_SPEED);
+
+		ballShape.dispose();
+	}
+
+	@Override
+	public void beginContact(Entity contacted) {
+		if (contacted instanceof Paddle) {
 			isCaught = true;
 		}
 	}
 
+	@Override
+	public void endContact(Entity contacted) {}
+
 	public abstract void activate();
 
-	public boolean isCaught() {
-		return isCaught;
-	}
 }

core/src/com/me/brickbuster/physics/Box2dContactListener.java

@@ -0,0 +1,53 @@
+package com.me.brickbuster.physics;
+
+import com.badlogic.gdx.physics.box2d.Contact;
+import com.badlogic.gdx.physics.box2d.ContactImpulse;
+import com.badlogic.gdx.physics.box2d.ContactListener;
+import com.badlogic.gdx.physics.box2d.Manifold;
+import com.me.brickbuster.entity.Entity;
+
+public class Box2dContactListener implements ContactListener {
+
+	@Override
+	public void beginContact(Contact contact) {
+		Object userDataA = contact.getFixtureA().getBody().getUserData();
+		Object userDataB = contact.getFixtureB().getBody().getUserData();
+
+		if (userDataA == null || userDataB == null ||
+				!(userDataA instanceof Entity) || !(userDataB instanceof Entity)) {
+			return;
+		}
+
+		if (userDataA instanceof CollisionListener) {
+			((CollisionListener) userDataA).beginContact((Entity) userDataB);
+		}
+		if (userDataB instanceof CollisionListener) {
+			((CollisionListener) userDataB).beginContact((Entity) userDataA);
+		}
+	}
+
+	@Override
+	public void endContact(Contact contact) {
+		Object userDataA = contact.getFixtureA().getBody().getUserData();
+		Object userDataB = contact.getFixtureB().getBody().getUserData();
+
+		if (userDataA == null || userDataB == null ||
+				!(userDataA instanceof Entity) || !(userDataB instanceof Entity)) {
+			return;
+		}
+
+		if (userDataA instanceof CollisionListener) {
+			((CollisionListener) userDataA).endContact((Entity) userDataB);
+		}
+		if (userDataB instanceof CollisionListener) {
+			((CollisionListener) userDataB).endContact((Entity) userDataA);
+		}
+	}
+
+	@Override
+	public void preSolve(Contact contact, Manifold oldManifold) {}
+
+	@Override
+	public void postSolve(Contact contact, ContactImpulse impulse) {}
+
+}

core/src/com/me/brickbuster/physics/CollisionListener.java

@@ -0,0 +1,11 @@
+package com.me.brickbuster.physics;
+
+import com.me.brickbuster.entity.Entity;
+
+public interface CollisionListener {
+
+	void beginContact(Entity contacted);
+
+	void endContact(Entity contacted);
+
+}

core/src/com/me/brickbuster/physics/PhysicsBody.java

@@ -0,0 +1,11 @@
+package com.me.brickbuster.physics;
+
+import com.badlogic.gdx.physics.box2d.Body;
+
+public interface PhysicsBody {
+
+	void createBody();
+
+	Body getBody();
+
+}

core/src/com/me/brickbuster/state/PlayState.java

@@ -2,63 +2,125 @@ package com.me.brickbuster.state;
 
 import com.badlogic.gdx.Gdx;
 import com.badlogic.gdx.graphics.Color;
-import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
 import com.badlogic.gdx.math.MathUtils;
+import com.badlogic.gdx.math.Vector2;
+import com.badlogic.gdx.physics.box2d.*;
+import com.badlogic.gdx.utils.Array;
 import com.me.brickbuster.BrickBuster;
-import com.me.brickbuster.entity.Ball;
+import com.me.brickbuster.entity.*;
-import com.me.brickbuster.entity.Brick;
+import com.me.brickbuster.entity.powerup.PowerUp;
-import com.me.brickbuster.entity.Paddle;
+import com.me.brickbuster.entity.powerup.PowerUpType;
-import com.me.brickbuster.entity.powerup.*;
+import com.me.brickbuster.physics.Box2dContactListener;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
 
 public class PlayState extends State {
 
-	public static final int SHIELD_HEIGHT = 30;
+	public static final float PIXEL_PER_METER = 40f;    // Board dimension: 54x96 meters
+	public static final float BOARD_WIDTH = 54f;
+	public static final float BOARD_HEIGHT = 96f;
+	public static final float EDGE_PADDING = .125f;
+
 	public static final float POWERUP_CHANCE = 0.15f;
 
 	public static final int COLUMNS = 9;
 	public static final int ROWS = 8;
 
+	public static final Vector2 lowerLeftCorner =
+			new Vector2(EDGE_PADDING,EDGE_PADDING);
+	public static final Vector2 lowerRightCorner =
+			new Vector2(BrickBuster.BOARD_WIDTH/PIXEL_PER_METER-EDGE_PADDING,EDGE_PADDING);
+	public static final Vector2 upperRightCorner =
+			new Vector2(BrickBuster.BOARD_WIDTH/PIXEL_PER_METER-EDGE_PADDING, BrickBuster.BOARD_HEIGHT/PIXEL_PER_METER-EDGE_PADDING);
+	public static final Vector2 upperLeftCorner =
+			new Vector2(EDGE_PADDING, BrickBuster.BOARD_HEIGHT/PIXEL_PER_METER-EDGE_PADDING);
+
+	public World world;
+
+	public Body playArea;
+	public Array<Body> bodies;
+
 	public List<PowerUp> powerUps;
 	public Paddle paddle;
 	public List<Ball> balls;
 	public List<Brick> bricks;
+	public List<Shield> shields;
 
-	private int shieldCount = 0;
 	private float updateTime = 0f;
 
+	private final Box2DDebugRenderer debugRenderer;
+
 	public PlayState(BrickBuster game) {
 		super(game);
+		debugRenderer = new Box2DDebugRenderer();
 	}
 
 	@Override
 	public void setup() {
+		// Initialize a world with no gravity
+		world = new World(new Vector2(), false);
+		world.setContactListener(new Box2dContactListener());
+
+		// define a playArea body with position set to 0
+		BodyDef playAreaDef = new BodyDef();
+		playAreaDef.type = BodyDef.BodyType.StaticBody;
+		playAreaDef.position.set(new Vector2());
+
+		EdgeShape screenEdge = new EdgeShape();
+
+		playArea = world.createBody(playAreaDef);
+		// Right edge
+		screenEdge.set(lowerRightCorner, upperRightCorner);
+		playArea.createFixture(screenEdge, 0f);
+		// Top edge
+		screenEdge.set(upperRightCorner, upperLeftCorner);
+		playArea.createFixture(screenEdge, 0f);
+		// Left edge
+		screenEdge.set(upperLeftCorner, lowerLeftCorner);
+		playArea.createFixture(screenEdge, 0f);
+		// Bottom edge
+		//screenEdge.set(lowerLeftCorner, lowerRightCorner);
+		//playArea.createFixture(screenEdge, 0f);
+		screenEdge.dispose();
+
 		powerUps = new ArrayList<PowerUp>();
 		paddle = new Paddle(this);
 
-		int brick_padding = (BrickBuster.BOARD_WIDTH - COLUMNS * Brick.BRICK_WIDTH) / (COLUMNS + 1);
+		float brick_padding = ((BrickBuster.BOARD_WIDTH/PIXEL_PER_METER) - COLUMNS * Brick.BRICK_WIDTH) / (COLUMNS + 1);
 		bricks = new ArrayList<Brick>();
 		for (int col = 0; col < COLUMNS; col++) {
 			for (int row = 0; row < ROWS; row++) {
-				int x = brick_padding + (col * (Brick.BRICK_WIDTH + brick_padding));
+				float x = brick_padding + (col * (Brick.BRICK_WIDTH + brick_padding));
-				int y = brick_padding + Brick.BRICK_HEIGHT + (row * (Brick.BRICK_HEIGHT + brick_padding));
+				float y = brick_padding + Brick.BRICK_HEIGHT + (row * (Brick.BRICK_HEIGHT + brick_padding));
 
 				PowerUpType powerUpType = null;
 				if (MathUtils.randomBoolean(POWERUP_CHANCE)) {
 					powerUpType = PowerUpType.getWeightedRandom();
 				}
 
-				bricks.add(new Brick(this, powerUpType, x, BrickBuster.BOARD_HEIGHT - y));
+				bricks.add(new Brick(this, powerUpType, x, BrickBuster.BOARD_HEIGHT/PIXEL_PER_METER - y));
 			}
 		}
 
 		balls = new ArrayList<Ball>();
 		balls.add(new Ball(this));
+
+		shields = new ArrayList<Shield>();
 	}
 
 	@Override
 	public void render() {
+		Array<Body> bodies = new Array<Body>();
+		world.getBodies(bodies);
+		for (Body b : bodies) {
+			Entity e = (Entity) b.getUserData();
+			if (e instanceof Ball || e instanceof PowerUp) {
+				e.setPos(b.getPosition());
+			}
+		}
+
 		long start = System.nanoTime();
 		for (Brick block : bricks) {
 			block.render(game.sr);
@@ -69,14 +131,12 @@ public class PlayState extends State {
 		for (Ball ball : balls) {
 			ball.render(game.sr);
 		}
+		for (Shield shield : shields) {
+			shield.render(game.sr);
+		}
 		paddle.render(game.sr);
 
-		if (getShieldCount() > 0) {
+		//debugRenderer.render(world, game.cam.combined.cpy().scl(PIXEL_PER_METER));
-			game.sr.begin(ShapeType.Filled);
-			game.sr.setColor(Color.SALMON);
-			game.sr.rect(0, 0, BrickBuster.BOARD_WIDTH, getShieldCount() * SHIELD_HEIGHT);
-			game.sr.end();
-		}
 		long renderTime = System.nanoTime() - start;
 
 		game.sb.begin();
@@ -94,8 +154,9 @@ public class PlayState extends State {
 		for (Iterator<Ball> it = balls.iterator(); it.hasNext();) {
 			Ball ball = it.next();
 			ball.update(dt);
-			if (ball.isDead()) {
+			if (ball.isDeleted()) {
 				it.remove();
+				world.destroyBody(ball.getBody());
 			}
 		}
 		if (balls.isEmpty()) {
@@ -105,15 +166,36 @@ public class PlayState extends State {
 		for (Iterator<PowerUp> it = powerUps.iterator(); it.hasNext();) {
 			PowerUp powerUp = it.next();
 			powerUp.update(dt);
-			if(powerUp.isCaught()) {
+			if(powerUp.isDeleted()) {
 				it.remove();
+				world.destroyBody(powerUp.getBody());
 			}
 		}
 
+		for (Iterator<Shield> it = shields.iterator(); it.hasNext();) {
+			Shield shield = it.next();
+			shield.update(dt);
+			if(shield.isDeleted()) {
+				it.remove();
+				world.destroyBody(shield.getBody());
+			}
+		}
+
+		for (Iterator<Brick> it = bricks.iterator(); it.hasNext();) {
+			Brick brick = it.next();
+			brick.update(dt);
+			if (brick.isDeleted()) {
+				it.remove();
+				world.destroyBody(brick.getBody());
+			}
+		}
 		if (bricks.isEmpty()) {
 			game.setScreen(new MenuState(game));
 			dispose();
+			return;
 		}
+
+		world.step(dt, 6, 2);
 		updateTime = System.nanoTime() - start;
 	}
 
@@ -121,6 +203,8 @@ public class PlayState extends State {
 	public void dispose() {
 		super.dispose();
 
+		world.dispose();
+
 		powerUps.clear();
 		powerUps = null;
 		balls.clear();
@@ -131,25 +215,25 @@ public class PlayState extends State {
 	}
 
 	public int getShieldCount() {
-		return shieldCount;
+		return shields.size();
 	}
 
 	public void addShield() {
-		shieldCount++;
+		Shield shield = new Shield(this);
-		paddle.setY(paddle.getY() + SHIELD_HEIGHT);
+		shields.add(shield);
+		paddle.setY(paddle.getY() + Shield.SHIELD_HEIGHT);
 		for (Ball ball : balls) {
 			if (ball.isStuck()) {
-				ball.setY(ball.getY() + SHIELD_HEIGHT);
+				ball.setY(ball.getY() + Shield.SHIELD_HEIGHT);
 			}
 		}
 	}
 
-	public void removeShield() {
+	public void removeShield(Shield shield) {
-		shieldCount--;
+		paddle.setY(paddle.getY() - Shield.SHIELD_HEIGHT);
-		paddle.setY(paddle.getY() - SHIELD_HEIGHT);
 		for (Ball ball : balls) {
 			if (ball.isStuck()) {
-				ball.setY(ball.getY() - SHIELD_HEIGHT);
+				ball.setY(ball.getY() - Shield.SHIELD_HEIGHT);
 			}
 		}
 	}