关于cc.TiledLayer渲染问题请求解答

let vertices = {};
const rows = 10; // 地图总行数
const cols = 10; // 地图总列数
const maptw2 = 32; // tiled宽
let rightTop = {};
rightTop.row = -1;
rightTop.col = -1;
for(let row=0;row<rows;++row){
	for(let col=0;col<cols;++col){
		let cullingCol = rows + col - row - 1;
		let cullingRow = rows + cols - col - row - 2;
        let left = maptw2 * cullingCol;
		let rowData = vertices[cullingRow] = vertices[cullingRow] || {minCol:0, maxCol:0};
		let colData = rowData[cullingCol] = rowData[cullingCol] || {};
		// record each row range, it will faster when culling grid
		if (rowData.minCol > cullingCol) {
			rowData.minCol = cullingCol;
		}

		if (rowData.maxCol < cullingCol) {
			rowData.maxCol = cullingCol;
		}

		// record max rect, when viewPort is bigger than layer, can make it smaller
		if (rightTop.row < cullingRow) {
			rightTop.row = cullingRow;
		}

		if (rightTop.col < cullingCol) {
			rightTop.col = cullingCol;
		}
        colData.left = left;
		colData.col = col;
		colData.row = row;
	}
}

这段伪代码来自CCTiledLayer.js的_updateVertices方法
请求大佬解答vertices[row][col]获取的是什么值?为什么该值可以判断是否可以优先渲染userNode?

@jare @jjyinkailejj

主要是想解决tiledmap层级遮挡的问题
image