maptalks-gl-layers 有文档手册吗？我们现在有一个2D的底图， 还有一个3D的部分区域图Geo3DTilesLayer，这俩个要叠加，目前这俩会互相覆盖，二者只显示其一，有办法解决吗

[hellofancycn]

maptalks's version and what browser you use?

Issue description

Please provide a reproduction URL (on any jsfiddle like site)