C++学习（三零七）AttributeDispatchers详解

Posted 2021-08-07 hankern

AttributeDispatchers称为属性调度器，用于将Geometry中的顶点属性（位置、颜色、法线等）派发到opengl中，用于几何图形的绘制。

AttributeDispatch属性调度类基类，又分为TemplateAttributeDispatch、TemplateTargetAttributeDispatch，由他们通过重载函数operator()执行具体的派发工作。

主要有如下几个类：

1、AttributeDispatch（属性调度）

osg/AttributeDispatchers
struct AttributeDispatch : public osg::Referenced
{
    virtual void assign(const GLvoid*) {}
    virtual void operator() (unsigned int) {};
};

2、TemplateAttributeDispatch

osg/AttributeDispatchers.cpp
template<typename T>
class TemplateAttributeDispatch : public AttributeDispatch
{}

3、TemplateTargetAttributeDispatch

osg/AttributeDispatchers.cpp
template<typename I, typename T>
class TemplateTargetAttributeDispatch : public AttributeDispatch
{
        typedef void (GL_APIENTRY * F) (I, const T*);
        virtual void operator () (unsigned int pos)
        {
            _functionPtr(_target, &(_array[pos * _stride]));
        }    
        F                       _functionPtr;
}

4、AttributeDispatchMap

osg/AttributeDispatchers.cpp
class AttributeDispatchMap
{}

2、AttributeDispatchers（属性调度器）

用于管理将各种属性数组（例如存储在 osg::Geometry 中）分派到 OpenGL 的助手类。

osg/AttributeDispatchers
/** Helper class for managing the dispatch to OpenGL of various attribute arrays such as stored in osg::Geometry.*/
class OSG_EXPORT AttributeDispatchers : public osg::Referenced
{}

生成

使用

在osg的状态机中定义了，AttributeDispatchers

osg/State
class OSG_EXPORT State : public Referenced
{
    /** Get the helper class for dispatching osg::Arrays as OpenGL attribute data.*/
    inline AttributeDispatchers& getAttributeDispatchers() { return _arrayDispatchers; }
    AttributeDispatchers            _arrayDispatchers;
}