[Solved] Why is there the need for the index argument in glEnableVertexAttribArray? [duplicate]

Question

Because it’s possible to set a vertex attribute to a value that’s constant for all elements using glVertexAttrib. Yes, you could to that to the same effect with a uniform as well, but this kind of per-attribute selection of where a value comes from (sourced from array, or set constant) has been around for ages (ever since OpenGL-1.1, although back then it was not generic attributes, but specific ones, i.e. position, color, normal and so on) and this legacy rubbed of onto generic vertex attributes.

Accepted Answer

Because it’s possible to set a vertex attribute to a value that’s constant for all elements using glVertexAttrib. Yes, you could to that to the same effect with a uniform as well, but this kind of per-attribute selection of where a value comes from (sourced from array, or set constant) has been around for ages (ever since OpenGL-1.1, although back then it was not generic attributes, but specific ones, i.e. position, color, normal and so on) and this legacy rubbed of onto generic vertex attributes.