typedef void (* XPLMMapDrawingCallback_f)( XPLMMapLayerID inLayer, const float * inMapBoundsLeftTopRightBottom, float zoomRatio, float mapUnitsPerUserInterfaceUnit, XPLMMapStyle mapStyle, XPLMMapProjectionID projection, void * inRefcon);
This is the OpenGL map drawing callback for plugin-created map layers. You can perform arbitrary OpenGL drawing from this callback, with one exception: changes to the Z-buffer are not permitted, and will result in map drawing errors.
All drawing done from within this callback appears beneath all built-in X-Plane icons and labels, but above the built-in “fill” layers (layers providing major details, like terrain and water). Note, however, that the relative ordering between the drawing callbacks of different plugins is not guaranteed.