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1、第八章 碰撞檢測與運動模擬
基于Box2D的游戲?qū)嵗?
（一）基礎(chǔ)知識
物理模擬、精靈的繪制與移動、觸摸事件的應(yīng)用
（1） 繪制游戲界面
（2） 通過單點觸摸屏幕，球桿瞄準(zhǔn)目標(biāo)
（3） 設(shè)置能量條（觸屏檢測）
（4） 球桿擊球
（5） 碰撞檢測（物理模擬）
（二）游戲配置文件
游戲需要新建一個Config.h的頭文件，此文件用來定義游戲中需要的參數(shù)。
#include "cocos2d.h"
USING_NS_CC;
using namespace cocos2d;
#define PTM_RATIO 32 // 定義32像素代表1米
static c
2、onst int SLIDER_BG_TAG = 1000;
static const int SLIDER_TAG = 1001;
static const int DASH_LINE_TAG = 1002;
static const int MAIN_BILLIARDS_TAG = 1003;
static const int AIM_ICON_TAG = 1004;
static const int AIM_GAN_TAG = 1005;
static const int MAX_SPEED = 2600;
static const std::string ball
3、[5] = {
"Chapter07/Ball/3.png",
"Chapter07/Ball/4.png",
"Chapter07/Ball/5.png",
"Chapter07/Ball/6.png",
"Chapter07/Ball/10.png"
};
static const Vec2 ballPos[] = {
Vec2(300,500),
Vec2(500,300),
Vec2(100,600),
Vec2(600,100),
Vec2(800,500)
};
（三）物理場景的繪制
由PhysicsScene.h類實現(xiàn)
4、，這里具體給出其實現(xiàn)，定義均在實現(xiàn)文件中實現(xiàn)了。
PhysicsScene.cpp
#include "PhysicsScene.h"
PhysicsScene::PhysicsScene(){}
PhysicsScene::~PhysicsScene(){}
bool PhysicsScene::init()
{
if (!Layer::init())
{
return false;
}
// physics scene
Size visibleSize = Director::getInstance()->getVisibleSize();
5、
Vec2 origin = Director::getInstance()->getVisibleOrigin();
// 定義世界的邊界
auto body = PhysicsBody::createEdgeBox(visibleSize,
PHYSICSBODY_MATERIAL_DEFAULT,5.0f);
auto edgeNode = Node::create();
edgeNode->setPosition(Vec2(visib
6、leSize.width/2,visibleSize.height/2));
edgeNode->setPhysicsBody(body);
this->addChild(edgeNode);
// 屏幕觸摸
auto listener = EventListenerTouchOneByOne::create();
listener->onTouchBegan = CC_CALLBA
7、CK_2(PhysicsScene::onTouchBegan, this);
Director::getInstance()->getEventDispatcher()->addEventListenerWithSceneGraphPriority(listener, this);
return true;
}
Scene* PhysicsScene::createScene()
{
// 創(chuàng)建物理世界
auto scene = Scene::createWithPhysics();
// 繪制調(diào)試遮罩
// scene->getPhysicsWor
8、ld()->setDebugDrawMask(PhysicsWorld::DEBUGDRAW_ALL);
auto layer = PhysicsScene::create();
scene->addChild(layer);
return scene;
}
bool PhysicsScene::onTouchBegan(Touch *touch, Event *unused_event)
{
Vec2 location = touch->getLocation();
addNewSpriteAtPosition(location);
return fal
9、se;
}
void PhysicsScene::addNewSpriteAtPosition(Vec2 p)
{
int picpath = rand() % 11;
auto sp = Sprite::create(StringUtils::format("Chapter07/Ball/%d.png",picpath));
sp->setTag(1);
auto body = PhysicsBody::createCircle(sp->getContentSize().width / 2);
// auto body = PhysicsBody::cre
10、ateBox(sp->getContentSize());
sp->setPhysicsBody(body);
sp->setPosition(p);
this->addChild(sp);
}
（四）物理物體的封裝，桌球的實現(xiàn)
由BilliardSprite.h類實現(xiàn)，這里具體給出其實現(xiàn)，定義均在實現(xiàn)文件中實現(xiàn)了。
BilliardSprite.cpp
#include "BilliardSprite.h"
BilliardSprite::BilliardSprite(){}
void BilliardSpri
11、te::update(float t)
{
_sprite->setPosition(Vec2(
_body->GetPosition().x * PTM_RATIO,
_body->GetPosition().y * PTM_RATIO));
_sprite->setRotation(-1 * CC_RADIANS_TO_DEGREES(_body->GetAngle()));
}
BilliardSprite::~BilliardSprite()
{
if (_name != NULL)
{
_name = NULL;
}
}
Bi
12、lliardSprite* BilliardSprite::create(char* name, bool isStatic, bool isBullet,
b2World* world, std::string picPath, Vec2 position,
float density /*= 1.0*/,
float friction /*= 0.1*/,
float restitution /*= 0.78 */)
{
BilliardSprite *pRet = new(std::nothrow) B
13、illiardSprite();
if (pRet && pRet->init(name, isStatic, isBullet, world, picPath,
position, density, friction, restitution)) {
pRet->autorelease();
return pRet;
}
else {
delete pRet;
pRet = NULL;
return NULL;
}
}
bool BilliardSprite::init(char* name, bool isStatic,
14、 bool isBullet,
b2World* world, std::string picPath, Vec2 position,
float density /*= 1.0*/,
float friction /*= 0.1*/,
float restitution /*= 0.78*/)
{
if (!Sprite::init())
{
return false;
}
_name = name;
// 創(chuàng)建精靈
_sprite = Sprite::create(picPath);
th
15、is->addChild(_sprite);
// bodyDef
b2BodyDef bodyDef;
if (!isStatic)
{
bodyDef.type = b2_dynamicBody;
}
if (isBullet)
{
bodyDef.bullet = true;
}
bodyDef.position.Set(position.x / PTM_RATIO,position.y / PTM_RATIO);
// 創(chuàng)建body
_body = world->CreateBody(&bodyDef);
_bo
16、dy->SetUserData(this);
b2CircleShape circle;
circle.m_radius = (_sprite->getContentSize().width / 2 ) / PTM_RATIO;
if (isStatic)
{
// 靜態(tài)
_body->CreateFixture(&circle,0.0f);
} else
{
// 動態(tài)
b2FixtureDef fixtureDef;
fixtureDef.shape = &circle;
fixtureDef.density = densit
17、y;
fixtureDef.friction = friction;
fixtureDef.restitution = restitution;
_body->CreateFixture(&fixtureDef);
}
this->scheduleUpdate();
return true;
}
（五）碰撞監(jiān)聽
由GameContactListener.h類實現(xiàn)，這里具體給出其實現(xiàn)，定義均在實現(xiàn)文件中實現(xiàn)了。
GameContactListener.cpp
#include "GameContactListener.h"
#include "B
18、illiardSprite.h"
GameContactListener::GameContactListener(){}
GameContactListener::~GameContactListener(){}
void GameContactListener::BeginContact(b2Contact*contact)
{
CCLOG("%s",static_cast(contact->GetFixtureA()->GetBody()->GetUserData())->getName());
CCLOG("%s",stat
19、ic_cast(contact->GetFixtureB()->GetBody()->GetUserData())->getName());
}
void GameContactListener::EndContact(b2Contact* contact)
{
// handle end event
}
void GameContactListener::PreSolve(b2Contact* contact,const b2Manifold* oldManifold)
{
// handle pre-solve event
}
20、
void GameContactListener::PostSolve(b2Contact* contact,const b2ContactImpulse* impulse)
{
// handle post-solve event
}
void GameContactListener::deleteBody(){}
（六）初始化物理世界
PhysicsBox2dScene.cpp文件中
void PhysicsBox2dScene::initPhysics()
{
Size s = Director::getInstance()->getVisibleS
21、ize();
_ContactListener = new GameContactListener();
// gravity
b2Vec2 gravity;
gravity.Set(0.0f, 0.0f);
// create world
_world = new b2World(gravity);
_world->SetContactListener(_ContactListener); // 碰撞
// allow sleep
_world->SetAllowSleeping(true);
// physics test 避
22、免碰撞檢測不連續(xù)產(chǎn)生碰撞穿透
_world->SetContinuousPhysics(true);
// ground
b2BodyDef groundBodyDef;
// left down
groundBodyDef.position.Set(0, 0);
// create ground
b2Body* groundBody = _world->CreateBody(&groundBodyDef);
groundBody->SetUserData("boundary");
// shape
b2EdgeShape groundB
23、ox;
// down
groundBox.Set(b2Vec2(0,0),b2Vec2(s.width/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);
// up
groundBox.Set(b2Vec2(0,s.height/PTM_RATIO),
b2Vec2(s.width/PTM_RATIO,s.height/PTM_RATIO));
groundBody->CreateFixture(&groundBox,0);
// left
groundBox.Set(b2Vec2
24、(0,s.height/PTM_RATIO),b2Vec2(0,0));
groundBody->CreateFixture(&groundBox,0);
// right
groundBox.Set(b2Vec2((s.width - 60)/PTM_RATIO,s.height/PTM_RATIO),b2Vec2((s.width - 60)/PTM_RATIO,0));
groundBody->CreateFixture(&groundBox,0);
}
（七）初始化場景
初始化：
PhysicsBox2dScene::PhysicsBox2dScene(
25、)
{
_world = NULL;
_aim = false;
_angle = 0.0f;
_curPower = 0.0f;
_powerEnd = false;
_sliderSpeed = 0.0f;
_aimPos = Vec2(-1,-1);
_canAim = true;
}
在PhysicsBox2dScene.cpp文件中init函數(shù)中初始化場景：
1、繪制能量條
// slider bg
auto slider_bg = Sprite::create("Chapter07/slider/bg-f.png");
sli
26、der_bg->setPosition(Vec2(visibleSize.width - 30, visibleSize.height/2));
this->addChild(slider_bg, 2, SLIDER_BG_TAG);
// init power slider rect
_powerRect = Rect(visibleSize.width - 58, 0,
58,visibleSize.height);
// slider
auto slider = Sprite::create("Chapter07/slider/fg-f.png")
27、;
this->addChild(slider, 3, SLIDER_TAG);
slider->setVisible(false);
// slider left
auto slider_left = Sprite::create("Chapter07/slider/bg-left.png");
slider_left->setPosition(Vec2(visibleSize.width - 60, visibleSize.height/2));
this->addChild(slider_left, 2);
2、繪制非物理世界邊界
// slider
28、 left
auto slider_left = Sprite::create("Chapter07/slider/bg-left.png");
slider_left->setPosition(Vec2(visibleSize.width - 60, visibleSize.height/2));
this->addChild(slider_left, 2);
// boundary left
auto boundary_left = Sprite::create("Chapter07/slider/bg-left.png");
boundary_left->se
29、tPosition(Vec2(3, visibleSize.height/2));
this->addChild(boundary_left);
// boundary right
auto boundary_right = Sprite::create("Chapter07/slider/bg-left.png");
boundary_right->setPosition(Vec2(visibleSize.width - 2, visibleSize.height/2));
this->addChild(boundary_right, 2);
3、初始化瞄準(zhǔn)區(qū)域
30、（物理世界大?。?
// init aim rect
_aimRect = Rect(0, 0, visibleSize.width - 60, visibleSize.height);
4、初始化物理世界
// init physics world
this->initPhysics();
5、初始化桌球
// 白球
_mainBilliards = BilliardSprite::create("main", false, true, _world, "Chapter07/Ball/8.png", Vec2(200,visibleSize.height/2));
31、
this->addChild(_mainBilliards, 10, MAIN_BILLIARDS_TAG);
for (int i=0;i<5;i++)
{
auto ballSprite = BilliardSprite::create("ball",false, false, _world, ball[i], ballPos[i]);
this->addChild(ballSprite);
}
6、初始化添加瞄準(zhǔn)線、瞄準(zhǔn)圖片和球桿
// dash line
auto dashLine = Sprite::create("Chapter07/aim/do
32、t_line.png");
this->addChild(dashLine, 2, DASH_LINE_TAG);
dashLine->setAnchorPoint(Vec2(0.5, 0));
dashLine->setVisible(false);
// aim icon
auto aim_icon = Sprite::create("Chapter07/aim/aim.png");
this->addChild(aim_icon, 10, AIM_ICON_TAG);
aim_icon->setScale(0.4f);
aim_icon->setVis
33、ible(false);
// 球桿
auto aim_gan = Sprite::create("Chapter07/aim/gan-f.png");
this->addChild(aim_gan, 10, AIM_GAN_TAG);
aim_gan->setAnchorPoint(Vec2(0.5, 0));
aim_gan->setScale(0.6f);
aim_gan->setVisible(false);
（八）能量條的控制
1、能量條區(qū)域觸摸響應(yīng)事件的設(shè)置
設(shè)置觸摸開始時響應(yīng)的事件：
bool PhysicsBox2dScene::on
34、TouchBegan(Touch *touch, Event *unused_event)
{
if (_aimRect.containsPoint(touch->getLocation()) && _canAim)
{
_aim = true;
auto start_p = changePos(_mainBilliards->getPosition());
auto end_p = touch->getLocation();
updateLine(start_p, end_p);
}
_powerEnd = false;
r
35、eturn true;
}
設(shè)置觸摸移動時響應(yīng)的事件，分為兩種情況，一種是當(dāng)觸摸移動的區(qū)域的是非物理世界時，改變的是能量條的狀態(tài)；另一種情況是當(dāng)觸摸移動的區(qū)域的是物理世界區(qū)域時，改變的是球桿瞄準(zhǔn)的方向：
void PhysicsBox2dScene::onTouchMoved(Touch *touch, Event *unused_event)
{
auto slider_bg = (Sprite*)getChildByTag(SLIDER_BG_TAG);
if (_powerRect.containsPoint(touch->getStartLocation()) &&
36、 _aim)
{
_curPower = touch->getStartLocation().y - touch->getLocation().y;
if (_curPower<0) {
_curPower = 0;
}
else if( _curPower > slider_bg->getContentSize().height )
{
_curPower = slider_bg->getContentSize().height;
}
updatePowerSlider(_curPower);
}
else if (_
37、aimRect.containsPoint(touch->getStartLocation()) && _canAim)
{
if (_aimRect.containsPoint(touch->getLocation()))
{
auto start_p = changePos(_mainBilliards->getPosition());
auto end_p = touch->getLocation();
updateLine(start_p, end_p);
}
}
}
設(shè)置觸摸結(jié)束時響應(yīng)的事件：
void PhysicsBox
38、2dScene::onTouchEnded(Touch *touch, Event *unused_event)
{
if (_powerRect.containsPoint(touch->getLocation()) && _aim)
{
auto slider_bg = (Sprite*)getChildByTag(SLIDER_BG_TAG);
_sliderSpeed = _curPower / slider_bg->getContentSize().height * 50.0f;
// 擊球
auto start_p = changePos(_m
39、ainBilliards->getPosition());
auto end_p = _aimPos;
auto v = changePos((end_p - start_p).getNormalized());
float q = _curPower / slider_bg->getContentSize().height;
// 設(shè)置白球速度
_mainBilliards->SetLinearVelocity(b2Vec2(v.x * q * MAX_SPEED, v.y * q * MAX_SPEED));
auto dash_line = (
40、Sprite*)getChildByTag(DASH_LINE_TAG);
dash_line->setVisible(false);
auto aim_icon = (Sprite*)getChildByTag(AIM_ICON_TAG);
aim_icon->setVisible(false);
auto aim_gan = (Sprite*)getChildByTag(AIM_GAN_TAG);
aim_gan->setVisible(false);
// 擊球運動后,在所有物體都靜止之前無法再進(jìn)行瞄準(zhǔn)和擊球
_canAim = false;
41、
_aim = false;
_powerEnd = true; // 進(jìn)度條可以消除
}
}
2、為控制條添加監(jiān)聽
在PhysicsBox2dScene.cpp文件中init函數(shù)中
// add touch listener
auto listener = EventListenerTouchOneByOne::create();
listener->onTouchBegan = CC_CALLBACK_2(PhysicsBox2dScene::onTouchBegan, this);
listener->onTouchMoved = CC_CA
42、LLBACK_2(PhysicsBox2dScene::onTouchMoved, this);
listener->onTouchEnded = CC_CALLBACK_2(PhysicsBox2dScene::onTouchEnded, this);
Director::getInstance()->getEventDispatcher()->addEventListenerWithSceneGraphPriority(listener,this);
（九）改變球桿方向
b2Vec2 PhysicsBox2dScene::changePos(Vec2 pos)
{
r
43、eturn b2Vec2(pos.x/PTM_RATIO, pos.y/PTM_RATIO);
}
cocos2d::Vec2 PhysicsBox2dScene::changePos(b2Vec2 pos)
{
return Vec2(pos.x*PTM_RATIO, pos.y*PTM_RATIO);
}
（十）更新瞄準(zhǔn)線的位置和球桿位置
void PhysicsBox2dScene::updateLine(Vec2 start_p, Vec2 end_p)
{
_aimPos = end_p;
// update line
_angle = (_
44、aimPos - start_p).getNormalized().getAngle() ;
auto dashLine = (Sprite*)getChildByTag(DASH_LINE_TAG);
dashLine->setPosition(start_p);
dashLine->setTextureRect(Rect(0,0,2,abs((end_p - start_p).getLength())));
dashLine->setRotation(CC_RADIANS_TO_DEGREES(-_angle) + 90.0f);
dashLine->setVisibl
45、e(true);
// update aim icon
auto aim_icon = (Sprite*)getChildByTag(AIM_ICON_TAG);
aim_icon->setPosition(_aimPos);
aim_icon->setVisible(true);
// 計算球桿位置
auto aim_gan_pos = Vec2(
(((end_p - start_p).getLength() + 45) * start_p.x - 45 * end_p.x) / (end_p - start_p).getLength(),
((
46、(end_p - start_p).getLength() + 45) * start_p.y - 45 * end_p.y) / (end_p - start_p).getLength());
auto aim_gan = (Sprite*)getChildByTag(AIM_GAN_TAG);
aim_gan->setPosition(aim_gan_pos);
aim_gan->setRotation(CC_RADIANS_TO_DEGREES(-_angle) - 90.0f);
aim_gan->setVisible(true);
}
（十一）實現(xiàn)碰撞檢測
47、（物理模擬）
1、碰撞檢測（物理模擬）的實現(xiàn)函數(shù)
void PhysicsBox2dScene::update(float delta)
{
float timeStep = 1.0f / 60.0f; // 時間同步
int32 velocityIterations = 8; // 速度迭代次數(shù)
int32 positionIterations = 1; // 位置迭代次數(shù)
_world->Step(timeStep,velocityIterations,positionIterations);
_ContactListener->deleteBo
48、dy(); // 循環(huán)判定游戲輸贏
for (b2Body* Cur = _world->GetBodyList(); Cur; Cur = Cur->GetNext() )
{
if ( Cur->GetType() == b2_dynamicBody && Cur->IsAwake() == true )
{
// 模擬阻力
Cur->SetLinearVelocity(b2Vec2(Cur->GetLinearVelocity().x * 0.989, Cur->GetLinearVelocity().y * 0.989));
if( ab
49、s(Cur->GetLinearVelocity().x) < 0.5f && abs(Cur->GetLinearVelocity().y) < 0.5f )
{
Cur->SetAwake(false);
}
}
}
if (_powerEnd)
{
// 滑塊消失
if (_curPower !=0)
{
_curPower -= _sliderSpeed;
} else if (_curPower <= 0)
{
_curPower = 0.0f;
}
updatePowerSli
50、der(_curPower);
}
// 所有球靜止才可以進(jìn)行瞄準(zhǔn)
int awak = 0;
for (b2Body* Cur = _world->GetBodyList(); Cur; Cur = Cur->GetNext() )
{
if ( Cur->GetType() == b2_dynamicBody && Cur->IsAwake() == true )
{
awak ++;
}
}
if (awak == 0)
{
_canAim = true;
}
}
2、在PhysicsBox2dScene.cpp文件中init函數(shù)中添加定時刷新函數(shù)，實現(xiàn)物理模擬，碰撞檢測
// main loop
this->scheduleUpdate();
（十二）游戲運行效果如圖。
chapter8 實驗手冊
