The variable T is often used in Templates.
By using templates one can create functions that work on different data types. For instance , a sum function that takes int, float, double, etc. The type (int, float, double) is represented by the variable T (type).
In the case of ofPolyline it might be to accept 2D points (glm::vec2) and 3D points (glm::vec3)?
The documentation you see online is in part automatically generated. The tool generating the docs is probably not smart enough atm to show us something more useful than “T”. But if I enter
and I hover the mouse over
getNormalAtIndexInterpolated the tooltip (in QtCreator) indicates that the return value is actually a glm::vec3