typedef void (* XPLMMapIconDrawingCallback_f)(
                         XPLMMapLayerID       inLayer,    
                         const float *        inMapBoundsLeftTopRightBottom,    
                         float                zoomRatio,    
                         float                mapUnitsPerUserInterfaceUnit,    
                         XPLMMapStyle         mapStyle,    
                         XPLMMapProjectionID  projection,    
                         void *               inRefcon);    

This is the icon drawing callback that enables plugin-created map layers to draw icons using X-Plane’s built-in icon drawing functionality. You can request an arbitrary number of PNG icons to be drawn via XPLMDrawMapIconFromSheet() from within this callback, but you may not perform any OpenGL drawing here.

Icons enqueued by this function will appear above all OpenGL drawing (performed by your optional XPLMMapDrawingCallback_f), and above all built-in X-Plane map icons of the same layer type (“fill” or “markings,” as determined by the XPLMMapLayerType in your XPLMCreateMapLayer_t). Note, however, that the relative ordering between the drawing callbacks of different plugins is not guaranteed.