osg渲染属性和opengl的接口分析
inline void State::applyModeList(ModeMap& modeMap,const StateSet::ModeList& modeList)//对每一个渲染叶都调用一次
{
StateSet::ModeList::const_iterator ds_mitr = modeList.begin();
ModeMap::iterator this_mitr=modeMap.begin();
while (this_mitr!=modeMap.end() && ds_mitr!=modeList.end()) //modeList第二个变量是0,或者1,表示stateset::ON或者stateset::Off
{//从_modelList第一位遍历，分大于，等于，小于,由于firt是已经经过排序,所以可以分位三种情况考虑
if (this_mitr->first<ds_mitr->first) 因为this_mitr->first已经经过排序,this_mitr->first(最小的)小于ds_mitr->first,但ds_mitr->first可能与其它的
//this_mitr->first相等，所以ds_mitr->first可能在ModeList，也可能不在modelList
{
// note GLMode = this_mitr->first
ModeStack& ms = this_mitr->second;//modeMap。已经保存的确modeList第一个分量已经排过序
if (ms.changed)//处理的是this_mitr->first,属于_modeMap并传递给OpenGL, 只要改变的时候才能传递,change表示是否需要传递给openGL
{
ms.changed = false;//ms.changed是真的，说明已经处理过
if (!ms.valueVec.empty())//ms.valueVec是非空的
{
bool new_value = ms.valueVec.back() & StateAttribute::ON;
applyMode(this_mitr->first,new_value,ms);
}
else//ms.valueVect是空的说明是在本函数中插入的
{
// assume default of disabled.
applyMode(this_mitr->first,ms.global_default_value,ms);
}
}
++this_mitr;//增加this_mitr,重新遍历
}
else if (ds_mitr->first<this_mitr->first)//由于this_mitr->first是最小的，所以ds_mitr->first肯定小于所有的确modMap,所以一定是一个新的mode
{
// ds_mitr->first is a new mode, therefore
// need to insert a new mode entry for ds_mistr->first.
ModeStack& ms = modeMap[ds_mitr->first];//插入到this_mitr->first前
bool new_value = ds_mitr->second & StateAttribute::ON;//求与操作，是on或者off
applyMode(ds_mitr->first,new_value,ms);
// will need to disable this mode on next apply so set it to changed.
ms.changed = true;
++ds_mitr;
}
else//如果相等，则mode是相同的,检查override性
{
// this_mitr & ds_mitr refer to the same mode, check the override
// if any otherwise just apply the incoming mode.
ModeStack& ms = this_mitr->second;
//当前modmap是OVERRIDE,而当前modeList是PROJECTED,属于父节点，并且在收集状态的阶段已经push_back到valueVec里面，并且ds_mitr没有
保护
if (!ms.valueVec.empty() && (ms.valueVec.back() & StateAttribute::OVERRIDE) && !(ds_mitr->second & StateAttribute::PROTECTED))
{
// override is on, just treat as a normal apply on modes.
if (ms.changed)//上一次已经插入新的，并改变了
{
ms.changed = false;
bool new_value = ms.valueVec.back() & StateAttribute::ON;
applyMode(this_mitr->first,new_value,ms);
}
}
else
{
// no override on or no previous entry, therefore consider incoming mode.由于valueVec.empty() 是个空的，说明不是在pushState()里面用插入的
bool new_value = ds_mitr->second & StateAttribute::ON;//如果是protected类型，则直接使用当前的类型即可，父节点的被重复
if (applyMode(ds_mitr->first,new_value,ms))//如果返回false则传递给opengl,否则不传递给opengl,因为上次已经传递过了
{返回真说明已经glEnable或者glDisable.
ms.changed = true;
}
}
++this_mitr;
++ds_mitr;
}
}
经过以上遍历，modeMap或者modelList已经遍历完
// iterator over the remaining state modes to apply any previous changes.//遍历完毕后应用剩余的osg属性
for(;
this_mitr!=modeMap.end();
++this_mitr)
{
// note GLMode = this_mitr->first
ModeStack& ms = this_mitr->second;
if (ms.changed)
{
ms.changed = false;
if (!ms.valueVec.empty())
{
bool new_value = ms.valueVec.back() & StateAttribute::ON;
applyMode(this_mitr->first,new_value,ms);
}
else
{
// assume default of disabled.
applyMode(this_mitr->first,ms.global_default_value,ms);
}
}
}
// iterator over the remaining incoming modes to apply any new mode.
for(;
ds_mitr!=modeList.end();
++ds_mitr)
{
ModeStack& ms = modeMap[ds_mitr->first];//global_default_value ...opengl默认打开或者关闭的值
bool new_value = ds_mitr->second & StateAttribute::ON;
applyMode(ds_mitr->first,new_value,ms);
// will need to disable this mode on next apply so set it to changed.
ms.changed = true;
}
}