最近几天,我都在学习如何在Cocos2d-x3.2中使用OpenGL来实现对图形的渲染。在网上也看到了很多好的文章,我在它们的基础上做了这次的我个人认为比较完整的总结。当你了解了Cocos2d-x3.2中对图形渲染的流程,你就会觉得要学会写自己的shader才是最重要的。
第一,渲染流程从2.x到3.x的变化。
在2.x中,渲染过程是通过递归渲染树(Rendering tree)这种图关系来渲染关系图。递归调用visit()函数,并且在visit()函数中调用该节点的draw函数渲染各个节点,此时draw函数的作用是直接调用OpenGL代码进行图形的渲染。由于visit()和draw函数都是虚函数,所以要注意执行时的多态。那么我们来看看2.x版本中CCSprite的draw函数,如代码1。
代码1:
//这是cocos2d-2.0-x-2.0.4版本的CCSprite的draw函数
void CCSprite::draw(void)
{
CC_PROFILER_START_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");
CCAssert(!m_pobBatchNode, "If CCSprite is being rendered by CCSpriteBatchNode, CCSprite#draw SHOULD NOT be called");
CC_NODE_DRAW_SETUP();
ccGLBlendFunc( m_sBlendFunc.src, m_sBlendFunc.dst );
if (m_pobTexture != NULL)
{
ccGLBindTexture2D( m_pobTexture->getName() );
}
else
{
ccGLBindTexture2D(0);
}
//
// Attributes
//
ccGLEnableVertexAttribs( kCCVertexAttribFlag_PosColorTex );
#define kQuadSize sizeof(m_sQuad.bl)
long offset = (long)&m_sQuad;
// vertex
int diff = offsetof( ccV3F_C4B_T2F, vertices);
glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, kQuadSize, (void*) (offset + diff));
// texCoods
diff = offsetof( ccV3F_C4B_T2F, texCoords);
glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));
// color
diff = offsetof( ccV3F_C4B_T2F, colors);
glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
CHECK_GL_ERROR_DEBUG();
#if CC_SPRITE_DEBUG_DRAW == 1
// draw bounding box
CCPoint vertices[4]={
ccp(m_sQuad.tl.vertices.x,m_sQuad.tl.vertices.y),
ccp(m_sQuad.bl.vertices.x,m_sQuad.bl.vertices.y),
ccp(m_sQuad.br.vertices.x,m_sQuad.br.vertices.y),
ccp(m_sQuad.tr.vertices.x,m_sQuad.tr.vertices.y),
};
ccDrawPoly(vertices, 4, true);
#elif CC_SPRITE_DEBUG_DRAW == 2
// draw texture box
CCSize s = this->getTextureRect().size;
CCPoint offsetPix = this->getOffsetPosition();
CCPoint vertices[4] = {
ccp(offsetPix.x,offsetPix.y), ccp(offsetPix.x+s.width,offsetPix.y),
ccp(offsetPix.x+s.width,offsetPix.y+s.height), ccp(offsetPix.x,offsetPix.y+s.height)
};
ccDrawPoly(vertices, 4, true);
#endif // CC_SPRITE_DEBUG_DRAW
CC_INCREMENT_GL_DRAWS(1);
CC_PROFILER_STOP_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");
}那么我们也看看3.x中Sprite的draw函数,如代码2。
代码2:
void Sprite::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
// Don't do calculate the culling if the transform was not updated
_insideBounds = (flags & FLAGS_TRANSFORM_DIRTY) ? renderer->checkVisibility(transform, _contentSize) : _insideBounds;
if(_insideBounds)
{
_quadCommand.init(_globalZOrder, _texture->getName(), getGLProgramState(), _blendFunc, &_quad, 1, transform);
renderer->addCommand(&_quadCommand);
#if CC_SPRITE_DEBUG_DRAW
_customDebugDrawCommand.init(_globalZOrder);
_customDebugDrawCommand.func = CC_CALLBACK_0(Sprite::drawDebugData, this);
renderer->addCommand(&_customDebugDrawCommand);
#endif //CC_SPRITE_DEBUG_DRAW
}
}
从代码1和代码2的对比中,我们很容易就发现2.x版本中的draw函数直接调用OpengGL代码进行图形渲染,而3.x版本中draw的作用是把RenderCommand添加到CommandQueue中,至于这样做的好处是,实际的渲染API进入其中一个与显卡直接交流的有独立线程的RenderQueue。
从Cocos2d-x3.0开始,Cocos2d-x引入了新的渲染流程,它不像2.x版本直接在每一个node中的draw函数中直接调用OpenGL代码进行图形渲染,而是通过各种RenderCommand封装起来,然后添加到一个CommandQueue队列里面去,而现在draw函数的作用就是在此函数中设置好相对应的RenderCommand参数,然后把此RenderCommand添加到CommandQueue中。最后在每一帧结束时调用renderer函数进行渲染,在renderer函数中会根据ID对RenderCommand进行排序,然后才进行渲染。
下面我们来看看图1、图2,这两个图形象地表现了Cocos2d-x3.x下RenderCommand的封装与传递与及RenderCommand的排序。
图1:
图2:
上面所说的各个方面都有点零碎,下面就对渲染的整个流程来一个从头到尾的梳理吧。下面是针对3.2版本的,对于2.x版本的梳理不做梳理,因为我用的是3.2版本。
首先,我们Cocos2d-x的执行是通过Application::run()来开始的,如代码3,此代码目录中在xx\cocos2d\cocos\platform\对应平台的目录下,这是与多平台实现有关的类,关于如何实现多平台的编译,你可以参考《cocos2d-x3.2源码分析(一)类FileUtils--实现把资源放在Resources文件目录下达到多平台的引用
》中我对平台编译的分析。以防篇幅过长,只截取了重要部分,如需详解,可以直接查看源码。
代码3:
int Application::run()
{
...
director->mainLoop();
...
}从代码3中,它明显的启发着我们要继续追寻Director::mainLoop()函数。在Director中mainLoop()为纯函数,此子类DisplayLinkDirector才有其实现,如代码4。
代码4:
void DisplayLinkDirector::mainLoop()
{
//只有一种情况会调用到这里来,就是导演类调用end函数
if (_purgeDirectorInNextLoop)
{
_purgeDirectorInNextLoop = false;
//清除导演类
purgeDirector();
}
else if (! _invalid)
{//绘制
drawScene();
//清除当前内存池中对象,即池中每一个对象--_referenceCount
PoolManager::getInstance()->getCurrentPool()->clear();
}
}mainLoop是主线程调用的循环,其中drawScene()是绘制函数,接着我们继续追寻它的代码,如代码5。
代码5:
void Director::drawScene()
{
//计算间隔时间
calculateDeltaTime();
//忽略该帧如果时间间隔接近0
if(_deltaTime 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();
}
}从代码5中,我们看见visit()和render()函数的调用。其中visit()函数会调用draw()函数来向RenderQueue中添加RenderCommand,那么就继续追寻visit()的代码,如代码6。
代码6:
void Node::visit(Renderer* renderer, const Mat4 &parentTransform, uint32_t parentFlags)
{
// quick return if not visible. children won't be drawn.
if (!_visible)
{
return;
}
uint32_t flags = processParentFlags(parentTransform, parentFlags);
// IMPORTANT:
// To ease the migration to v3.0, we still support the Mat4 stack,
// but it is deprecated and your code should not rely on it
Director* director = Director::getInstance();
director->pushMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
director->loadMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW, _modelViewTransform);
int i = 0;
if(!_children.empty())
{
sortAllChildren();
// draw children zOrder _localZOrder visit(renderer, _modelViewTransform, flags);
else
break;
}
// self draw
this->draw(renderer, _modelViewTransform, flags);
for(auto it=_children.cbegin()+i; it != _children.cend(); ++it)
(*it)->visit(renderer, _modelViewTransform, flags);
}
else
{
this->draw(renderer, _modelViewTransform, flags);
}
director->popMatrix(MATRIX_STACK_TYPE::MATRIX_STACK_MODELVIEW);
// FIX ME: Why need to set _orderOfArrival to 0??
// Please refer to https://github.com/cocos2d/cocos2d-x/pull/6920
// reset for next frame
// _orderOfArrival = 0;
}从代码6中,我们可以看到“ auto node = _children.at(i);和node->visit(renderer, _modelViewTransform, flags);”,这段代码的意思是先获取子节点,然后递归调用节点的visit()函数,到了没有子节点的节点,开始调用draw()函数。那么我们看看draw()函数代码,如代码7。
代码7:
void Node::draw(Renderer* renderer, const Mat4 &transform, uint32_t flags)
{
}好吧,从代码7中,我们看到Node的draw什么都没有做,是我们找错地方?原来draw()是虚函数,所以它执行时执行的是该字节类的draw()函数。确实是我们找错地方了。那么我们分别看DrawNode::draw()、Sprite::draw()。
代码8:
void DrawNode::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
_customCommand.init(_globalZOrder);
_customCommand.func = CC_CALLBACK_0(DrawNode::onDraw, this, transform, flags);
renderer->addCommand(&_customCommand);
}
void Sprite::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
// Don't do calculate the culling if the transform was not updated
_insideBounds = (flags & FLAGS_TRANSFORM_DIRTY) ? renderer->checkVisibility(transform, _contentSize) : _insideBounds;
if(_insideBounds)
{
_quadCommand.init(_globalZOrder, _texture->getName(), getGLProgramState(), _blendFunc, &_quad, 1, transform);
renderer->addCommand(&_quadCommand);
#if CC_SPRITE_DEBUG_DRAW
_customDebugDrawCommand.init(_globalZOrder);
_customDebugDrawCommand.func = CC_CALLBACK_0(Sprite::drawDebugData, this);
renderer->addCommand(&_customDebugDrawCommand);
#endif //CC_SPRITE_DEBUG_DRAW
}
}
从代码8中,我们可以看到在draw()函数向RenderQueue中添加RenderCommand,当然有的类的draw()不是向RenderQueue中添加RenderCommand,而是直接使用OpenGL的API直接进行渲染,或者做一些其他的事情。
那么当draw()都递归调用完了,我们来看看最后进行渲染的Renderer::render() 函数,如代码9。
代码9:
void Renderer::render()
{
//Uncomment this once everything is rendered by new renderer
//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//TODO setup camera or MVP
_isRendering = true;
if (_glViewAssigned)
{
// cleanup
_drawnBatches = _drawnVertices = 0;
//Process render commands
//1. Sort render commands based on ID
for (auto &renderqueue : _renderGroups)
{
renderqueue.sort();
}
visitRenderQueue(_renderGroups[0]);
flush();
}
clean();
_isRendering = false;
}从代码9中,我们看到“renderqueue.sort()",这是之前所说的对命令先排序,然后才进行渲染,“visitRenderQueue( _renderGroups[0])”就是来进行渲染的。那么我们接着看看void Renderer::visitRenderQueue(const RenderQueue& queue)的代码,如代码10。
代码10:
void Renderer::visitRenderQueue(const RenderQueue& queue)
{
ssize_t size = queue.size();
for (ssize_t index = 0; index getType();
if(RenderCommand::Type::QUAD_COMMAND == commandType)
{
flush3D();
auto cmd = static_cast(command);
//Batch quads
if(_numQuads + cmd->getQuadCount() > VBO_SIZE)
{
CCASSERT(cmd->getQuadCount()>= 0 && cmd->getQuadCount() getQuads(), sizeof(V3F_C4B_T2F_Quad) * cmd->getQuadCount());
convertToWorldCoordinates(_quads + _numQuads, cmd->getQuadCount(), cmd->getModelView());
_numQuads += cmd->getQuadCount();
}
else if(RenderCommand::Type::GROUP_COMMAND == commandType)
{
flush();
int renderQueueID = ((GroupCommand*) command)->getRenderQueueID();
visitRenderQueue(_renderGroups[renderQueueID]);
}
else if(RenderCommand::Type::CUSTOM_COMMAND == commandType)
{
flush();
auto cmd = static_cast(command);
cmd->execute();
}
else if(RenderCommand::Type::BATCH_COMMAND == commandType)
{
flush();
auto cmd = static_cast(command);
cmd->execute();
}
else if (RenderCommand::Type::MESH_COMMAND == commandType)
{
flush2D();
auto cmd = static_cast(command);
if (_lastBatchedMeshCommand == nullptr || _lastBatchedMeshCommand->getMaterialID() != cmd->getMaterialID())
{
flush3D();
cmd->preBatchDraw();
cmd->batchDraw();
_lastBatchedMeshCommand = cmd;
}
else
{
cmd->batchDraw();
}
}
else
{
CCLOGERROR("Unknown commands in renderQueue");
}
}
}从代码10中,我们看到RenderCommand类型有QUAD_COMMAND,CUSTOM_COMMAND,BATCH_COMMAND,
GROUP_COMMAND,MESH_COMMAND五种,这些类型的讲解在下一节。
从代码10中,好像没有与OpenGL相关的代码,有点