OpenGL Tessellation回调未执行

Question

我使用这里的示例将我的曲面细分回调移动到另一个类.

代码编译,但回调代码永远不会执行.

回调类:

template <class Class, typename ReturnType, typename Parameter>
class SingularCallBack
{
public:

    typedef ReturnType (Class::*Method)(Parameter);

    SingularCallBack(Class* class_instance, Method method)
        : class_instance_(class_instance),
        method_(method)
    {}

    ReturnType operator()(Parameter parameter)
    {
        return (class_instance_->*method_)(parameter);
    }

    ReturnType execute(Parameter parameter)
    {
        return operator()(parameter);
    }

private:

    Class* class_instance_;
    Method method_;
};

回调:

void MyClass::tessBegin(GLenum which)
{
    glBegin(which);
    cout << "BEGIN CALLBACK IS WORKING";
}

void MyClass::tessVertex(const GLvoid *data)
{
    // cast back to double type
    const GLdouble *ptr = (const GLdouble*)data;

    glVertex3dv(ptr);
    cout << "VERTEX CALLBACK IS WORKING";
}

我正在注册的曲面细分功能:

int MyClass::TessellatePolys()
{
    GLUtesselator *tess = gluNewTess(); // create a tessellator
    if(!tess) return 0;  // failed to create tessellation object, return 0

    // register callback functions
    SingularCallBack<GLOrtho, void, GLenum>*BeginCallback;
    BeginCallback = new SingularCallBack<GLOrtho, void, GLenum>(this,&GLOrtho::tessBegin);
    gluTessCallback(tess, GLU_TESS_BEGIN, (void (CALLBACK *)())BeginCallback);

    SingularCallBack<GLOrtho, void, const GLvoid*>*VertexCallback;
    VertexCallback = new SingularCallBack<GLOrtho, void, const GLvoid*>(this,&GLOrtho::tessVertex);
    gluTessCallback(tess, GLU_TESS_VERTEX, (void (CALLBACK *)())VertexCallback);

    ... (do tessellation) ...

    return id;
}

回调的注册方式有什么问题？

Answer 1

您正在将指向对象类型的指针转​​换为指向函数类型的指针（例如，将“BeginCallback”转换为“void (CALLBACK *)()”）。这些类型是不兼容且不相关的。该代码按照 C 风格的强制转换进行编译，无需任何类型检查。更重要的是，从 C++ 编译器的角度来看，BeginCallback 和 VertexCallback 是不同且不兼容的类型，并且函数 gluTessCallback 无法调用它们的重载运算符（） - 这些是不同的成员函数。