osg学习（五十一）Warning: detected OpenGL error ‘invalid operation‘ at after RenderBin::draw(..)

原因是什么？

这个错误只出现一次，并且是在第一帧时出现。

Warning: detected OpenGL error 'invalid operation' after applying attribute Viewport 04292398

应该是执行报错

osg/Viewport.cpp
void Viewport::apply(State&) const
{
    glViewport( static_cast<GLint>(_x),static_cast<GLint>(_y),
                static_cast<GLsizei>(_width),static_cast<GLsizei>(_height) );
}

https://osg-users.openscenegraph.narkive.com/WV8ZHDLd/debugging-warning-detected-opengl-error-invalid-value-after-renderbin-draw

pState->setCheckForGLErrors(osg::State::CheckForGLErrors::ONCE_PER_ATTRIBUTE)

osg/State 
       enum CheckForGLErrors
        {
            /** NEVER_CHECK_GL_ERRORS hints that OpenGL need not be checked for, this
                is the fastest option since checking for errors does incur a small overhead.*/
            NEVER_CHECK_GL_ERRORS,
            /** ONCE_PER_FRAME means that OpenGL errors will be checked for once per
                frame, the overhead is still small, but at least OpenGL errors that are occurring
                will be caught, the reporting isn't fine grained enough for debugging purposes.*/
            ONCE_PER_FRAME,
            /** ONCE_PER_ATTRIBUTE means that OpenGL errors will be checked for after
                every attribute is applied, allow errors to be directly associated with
                particular operations which makes debugging much easier.*/
            ONCE_PER_ATTRIBUTE
        };

默认为：ONCE_PER_FRAME