osg求交，模型矩阵

Intersector* LineSegmentIntersector::clone(osgUtil::IntersectionVisitor& iv)
{
    if (_coordinateFrame==MODEL && iv.getModelMatrix()==0)
    {
        osg::ref_ptr<LineSegmentIntersector> lsi = new LineSegmentIntersector(_start, _end);
        lsi->_parent = this;
        return lsi.release();
    }

    // compute the matrix that takes this Intersector from its CoordinateFrame into the local MODEL coordinate frame
    // that geometry in the scene graph will always be in.//
    osg::Matrix matrix;
    switch (_coordinateFrame)
    {
        case(WINDOW):
            if (iv.getWindowMatrix()) matrix.preMult( *iv.getWindowMatrix() );
            if (iv.getProjectionMatrix()) matrix.preMult( *iv.getProjectionMatrix() );
            if (iv.getViewMatrix()) matrix.preMult( *iv.getViewMatrix() );
            if (iv.getModelMatrix()) matrix.preMult( *iv.getModelMatrix() );
            break;
        case(PROJECTION):
            if (iv.getProjectionMatrix()) matrix.preMult( *iv.getProjectionMatrix() );
            if (iv.getViewMatrix()) matrix.preMult( *iv.getViewMatrix() );
            if (iv.getModelMatrix()) matrix.preMult( *iv.getModelMatrix() );
            break;
        case(VIEW):
            if (iv.getViewMatrix()) matrix.preMult( *iv.getViewMatrix() );
            if (iv.getModelMatrix()) matrix.preMult( *iv.getModelMatrix() );
            break;
        case(MODEL):
            if (iv.getModelMatrix()) matrix = *iv.getModelMatrix();
            break;
    }

    osg::Matrix inverse;
    inverse.invert(matrix);

    osg::ref_ptr<LineSegmentIntersector> lsi = new LineSegmentIntersector(_start * inverse, _end * inverse);//把相交点转到模型矩阵

    //而模型本身不需要转换，其坐标就是在模型坐标系中的坐标,求得的交点也是在局部坐标系中的坐标
    lsi->_parent = this;
    return lsi.release();

  switch(mode)
        {
            case(GL_TRIANGLES):
            {
                const Vec3* vlast = &_vertexArrayPtr[first+count];                                   ///一个geometry下面挂几个drawable,每个drawable下有几个

                                                                                                                            //primitive，每一个primitive就在此循环一次求交
                for(const Vec3* vptr=&_vertexArrayPtr[first];vptr<vlast;vptr+=3)
                    this->operator()(*(vptr),*(vptr+1),*(vptr+2),_treatVertexDataAsTemporary);
                break;
            }
            case(GL_TRIANGLE_STRIP):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=2;i<count;++i,++vptr)
                {
                    if ((i%2)) this->operator()(*(vptr),*(vptr+2),*(vptr+1),_treatVertexDataAsTemporary);
                    else       this->operator()(*(vptr),*(vptr+1),*(vptr+2),_treatVertexDataAsTemporary);
                }
                break;
            }
            case(GL_QUADS):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=3;i<count;i+=4,vptr+=4)
                {
                    this->operator()(*(vptr),*(vptr+1),*(vptr+2),_treatVertexDataAsTemporary);
                    this->operator()(*(vptr),*(vptr+2),*(vptr+3),_treatVertexDataAsTemporary);
                }
                break;
            }
            case(GL_QUAD_STRIP):
            {
                const Vec3* vptr = &_vertexArrayPtr[first];
                for(GLsizei i=3;i<count;i+=2,vptr+=2)
                {
                    this->operator()(*(vptr),*(vptr+1),*(vptr+2),_treatVertexDataAsTemporary);
                    this->operator()(*(vptr+1),*(vptr+3),*(vptr+2),_treatVertexDataAsTemporary);
                }
                break;
            }
            case(GL_POLYGON): // treat polygons as GL_TRIANGLE_FAN
            case(GL_TRIANGLE_FAN):
            {
                const Vec3* vfirst = &_vertexArrayPtr[first];
                const Vec3* vptr = vfirst+1;
                for(GLsizei i=2;i<count;++i,++vptr)
                {
                    this->operator()(*(vfirst),*(vptr),*(vptr+1),_treatVertexDataAsTemporary);
                }
                break;
            }
            case(GL_POINTS):
            case(GL_LINES):
            case(GL_LINE_STRIP):
            case(GL_LINE_LOOP):
            default:
                // can't be converted into to triangles.
                break;
        }
    }
}