Custom Draw API is an extension of the AutoCAD ObjectARX (C++) API that allows us to customize the way AutoCAD Civil 3D renders objects. There is a sample application demonstrating this API which is part of the AutoCAD Civil 3D installation folder typically at <Civil 3D installation folder >\Sample\Civil 3D API\COM\VC++\CustomDraw\Lib\x64
In AutoCAD Civil 3D 2014 release, unfortunately the Custom Draw API lib file [ AeccCustomDraw.lib ] is missing. I am uploading this " AeccCustomDraw Lib" file here for those of you who want to use the same in Civil 3D 2014.