terrain_vertex* vecs = (terrain_vertex*)render::map_VBO(m_vbuffer, 0, m_vb_size * sizeof(terrain_vertex), MAP_WRITE);
                //uv range in terrain
                vec2  uv_area = thiz_node.m_info.m_end - thiz_node.m_info.m_start;
                vec2  uv_step = uv_area / vec2(m_detail_vertexs);
                //mapping
                #pragma omp parallel for num_threads(4)
                for (int y = 0; y < m_detail_vertexs.y; ++y)
                for (int x = 0; x < m_detail_vertexs.x; ++x)
                {
                    //vertex id
                    int vid = y * m_detail_vertexs.x + x;
                    assert(vid < m_vb_size);
                    //current uv
                    vec2 uv_coord(thiz_node.m_info.m_start + uv_step * vec2(x,y));
                    //get height
                    float height = get_height(uv_coord.x, uv_coord.y);
                    //pos
                    vec3 pos
                    {
                          uv_coord.x - 0.5
                        , height
                        , uv_coord.y - 0.5
                    };
                    //add new vertex
                    vecs[vid] = terrain_vertex
                    (
                        pos,
                        vec3(0, 1, 0),
                        uv_coord
                    );
                }
                render::unmap_VBO(m_vbuffer);