where is the code of Highlighting of tracks on mouse dragging

I want to use audacity code in my Project
So I want to know the location of the code of HIGHLIGHTING OF THE TRACK when user select the region on mouse drag. Where is the drawing taking place that HIGHLIGHT the selected region.

It’s mostly in TrackArtist.cpp, but the code is very specific to Audacity so I don’t expect it will be much help for other applications, other than perhaps providing some ideas.

I want to have multiple selection and the selection rectangle should have dotted boundaries and each rectangle must be of different colors.