Books/treatises on musical composition in the Renaissance and 20th/21st century

Hi,

I'm preparing my Bachelor's thesis which I have decided is going to be an in-depth study and comparison of composition techniques in the Renaissance era and in modern times. While I consider myself to be fairly well versed in the literature and have a decent idea what the conclusion will be, I'm not yet fully qualified to conduct my own research through score study and would like to read as many books on the topic as possible. Can anybody recommend treatises written by theorists of the time or books written by experts on the subject for me to read?

I'm looking for books such as Messiaen's "Technique of My Musical Language", which take the technique of composition under a microscope. It's best if it's written by a real practitioner but I realize there are not many of these from Renaissance times and will gladly accept expert research.

Thanks in advance.

"A Geometry of Music: Harmony and Counterpoint in the Extended Practice period."

by Dimitri Tymoczko

Chapters on Renaissance music, Oxford University Press 2001