cocos2D-X源码分析之从cocos2D-X学习OpenGL----cocos2D-X渲染结构

void DisplayLinkDirector::mainLoop()
{

// 这个标志在调用end()方法会设置为true
if (_purgeDirectorInNextLoop)
{

<span style="font-family:Consolas, Courier New, Courier, mono, serif;"><span style="line-height: 18px;">//只有一种情况会调用到这里来，就是导演类调用end函数</span></span>
_purgeDirectorInNextLoop = false;
purgeDirector();
}

//<span style="font-family: Arial, Helvetica, sans-serif;">startAnimation 设置为false, </span><span style="font-family: Arial, Helvetica, sans-serif;">stopAnimation 设置为 true</span><span style="font-family: Arial, Helvetica, sans-serif;">
</span>    else if (! _invalid)
{
drawScene();

// release the objects
PoolManager::getInstance()->getCurrentPool()->clear();
}
}//

void DisplayLinkDirector::stopAnimation()
{
_invalid = true;
}

// should we implement 4 types of director ??
// I think DisplayLinkDirector is enough
// so we now only support DisplayLinkDirector
void DisplayLinkDirector::startAnimation()
{
if (gettimeofday(_lastUpdate, nullptr) != 0)
{
CCLOG("cocos2d: DisplayLinkDirector: Error on gettimeofday");
}

_invalid = false;

Application::getInstance()->setAnimationInterval(_animationInterval);

// fix issue #3509, skip one fps to avoid incorrect time calculation.
setNextDeltaTimeZero(true);
}

// Draw the Scene
void Director::drawScene()
{
// calculate "global" dt
calculateDeltaTime();

// skip one flame when _deltaTime equal to zero.
if(_deltaTime < FLT_EPSILON)
{
return;
}

if (_openGLView)
{
_openGLView->pollInputEvents();
}

//tick before glClear: issue #533
if (! _paused)
{
_scheduler->update(_deltaTime);
_eventDispatcher->dispatchEvent(_eventAfterUpdate);
}

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

/* to avoid flickr, nextScene MUST be here: after tick and before draw.
XXX: Which bug is this one. It seems that it can't be reproduced with v0.9 */
if (_nextScene)
{
setNextScene();
}

pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);

// draw the scene
if (_runningScene)
{
_runningScene->visit(_renderer, Mat4::IDENTITY, false);
_eventDispatcher->dispatchEvent(_eventAfterVisit);
}

// draw the notifications node
if (_notificationNode)
{
_notificationNode->visit(_renderer, Mat4::IDENTITY, false);
}

if (_displayStats)
{
showStats();
}

_renderer->render();
_eventDispatcher->dispatchEvent(_eventAfterDraw);

popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);

_totalFrames++;

// swap buffers
if (_openGLView)
{
_openGLView->swapBuffers();
}

if (_displayStats)
{
calculateMPF();
}
}

void Director::calculateDeltaTime()
{

//大概是表示时间struct
struct timeval now;

//使用C语言编写程序需要获得当前精确时间（1970年1月1日到现在的时间）

//<span style="font-family: Arial, Helvetica, sans-serif;">其参数</span><span style="font-family: Arial, Helvetica, sans-serif;">now</span><span style="font-family: Arial, Helvetica, sans-serif;">是保存获取时间结果的结构体，第二个参数用于保存时区结果：可以传null</span><span style="font-family: Arial, Helvetica, sans-serif;">
</span>    if (gettimeofday(&now, nullptr) != 0)
{
CCLOG("error in gettimeofday");

//记录 自mainloop上次tick过去了多少时间
_deltaTime = 0;
return;
}

// new delta time. Re-fixed issue #1277

//是否下一个增量时间(<span style="font-family: Arial, Helvetica, sans-serif;">_deltaTime</span><span style="font-family: Arial, Helvetica, sans-serif;">)将是零</span>
if (_nextDeltaTimeZero)
{
_deltaTime = 0;
_nextDeltaTimeZero = false;
}
else
{

//计算过去了的时间，后面的微秒 <span style="font-family: Arial, Helvetica, sans-serif;">/ 1000000.0f</span>
_deltaTime = (now.tv_sec - _lastUpdate->tv_sec) + (now.tv_usec - _lastUpdate->tv_usec) / 1000000.0f;
_deltaTime = MAX(0, _deltaTime);
}

#if COCOS2D_DEBUG
// If we are debugging our code, prevent big delta time
if (_deltaTime > 0.2f)
{
_deltaTime = 1 / 60.0f;
}
#endif
//最后一次更新的时间
*_lastUpdate = now;
}

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#include <sys/time.h>int gettimeofday(struct timeval*tv, struct timezone *tz);其参数tv是保存获取时间结果的结构体，参数tz用于保存时区结果：struct timezone{int tz_minuteswest;/*格林威治时间往西方的时差*/int tz_dsttime;/*DST 时间的修正方式*/}timezone 参数若不使用则传入NULL即可。而结构体timeval的定义为：struct timeval{long int tv_sec; // 秒数long int tv_usec; // 微秒数}它获得的时间精确到微秒（1e-6 s)量级。在一段代码前后分别使用gettimeofday可以计算代码执行时间：struct timeval tv_begin, tv_end;gettimeofday(&tv_begin, NULL);foo();gettimeofday(&tv_end, NULL);