During the rendering process, two threads are used.One of them is responsible for generating multi-resolution terrain mesh by using quad-tree, flag matrix, and view frustum.

• 该阶段使用两个线程，其中绘制线程主要借助四叉树结构，标识矩阵，裁减视景体来实现四块子地形的多分辨率网格生成；