[ARX程序]：polysamp程序中moveGripPointsAt()的疑惑？

heluyuan

D:\objectarx2002\samples\polysamp\poly.cpp中源码如下：

Acad::ErrorStatus
AsdkPoly::moveGripPointsAt(
    const AcDbIntArray& indices,
    const AcGeVector3d& offset)
{
    if (indices.length()== 0 || offset.isZeroLength())
        return Acad::eOk; //that's easy :-)

    if (mDragDataFlags & kCloneMeForDraggingCalled) {
        mDragDataFlags |= kUseDragCache;
        // we need to make sure that all the poly's drag data members
        // are in sync with the true data members
        //
        //mDragCenter = mCenter;
        //mDragStartPoint = mStartPoint;
    } else
        // Only if we're not dragging do we want to make an undo
        // recording and check if the object's open for write.
        //
        assertWriteEnabled();

    //if there more than one hot vertex or there's one and it is the center
    //then simply transform
    if (indices.length()>1 || indices[0] == mNumSides)
        return transformBy(AcGeMatrix3d::translation(offset));
        
    AcGeVector3d off(offset);
    //calculate the offset vector of the startpoint
        //from the offset vector on a vertex
    double rotateBy = 2.0 * 3.14159265358979323846 / mNumSides * indices[0];
    AcGePoint3d cent;
    getCenter(cent);
    off.transformBy(AcGeMatrix3d::rotation(-rotateBy,normal(),cent));
     acdbWcs2Ecs(asDblArray(off),asDblArray(off),asDblArray(normal()),Adesk::kTrue);
    if (mDragDataFlags & kUseDragCache){
        mDragCenter = mCenter;
        mDragPlaneNormal = mPlaneNormal;
        mDragStartPoint = mStartPoint + AcGeVector2d(off.x,off.y);
        mDragElevation = mElevation + off.z;
    }else{
        mStartPoint = mStartPoint + AcGeVector2d(off.x,off.y);
        mElevation = mElevation + off.z;
    }
    return Acad::eOk;
}


请问程序中后面的代码实现什么功能?
    double rotateBy = 2.0 * 3.14159265358979323846 / mNumSides * indices[0];
    AcGePoint3d cent;
    getCenter(cent);
    off.transformBy(AcGeMatrix3d::rotation(-rotateBy,normal(),cent));
     acdbWcs2Ecs(asDblArray(off),asDblArray(off),asDblArray(normal()),Adesk::kTrue);
    if (mDragDataFlags & kUseDragCache){
        mDragCenter = mCenter;
        mDragPlaneNormal = mPlaneNormal;
        mDragStartPoint = mStartPoint + AcGeVector2d(off.x,off.y);
        mDragElevation = mElevation + off.z;
    }else{
        mStartPoint = mStartPoint + AcGeVector2d(off.x,off.y);
        mElevation = mElevation + off.z;
    }
    return Acad::eOk;