Musical form and orchestration are closely related dimensions of the musical discourse. Despite the proposition of several practical tools for assisted-orchestration in the past few years, scarcely any computational methods for analyzing the role of orchestration in shaping musical form and its perception have been put forward. As an answer to that, in this presentation, we discuss a couple of Open-Music functions we designed for estimating the textural complexity of a piece's successive formal segments and sections. The calculations behind the functions originate in an appropriation of the mathematical theory of integer partitions and Wallace Berry's ideas on musical texture. In the current stage, our estimation of textural complexity is carried out upon the composer's prescriptions found on the musical score. Nevertheless, the work we present here is part of an overall model that ultimately aims to analyze form and orchestration combining symbolical and signal data, that is, joining the musical score and its performance recordings.