Please note that I am not very familiar with the Opengl library ...

What is the 2.1 equivalent of "glDrawElementsInstanced" ?

This recently popped up on a test as being incompatible with 2.x graphics cards.

        for (int i = 0; i < primcount ; i++) {
            instanceID = i;//pass to shader somehow
            glDrawElements(mode, count, type, indices);
        }

There isn't, but it's probably worth checking for the extension even in a 2.x context:

https://www.opengl.org/registry/specs/ARB/draw_instanced.txt

Please note that I am not very familiar with the Opengl library ...

What is the 2.1 equivalent of "glDrawElementsInstanced" ?

This recently popped up on a test as being incompatible with 2.x graphics cards.

https://www.opengl.org/registry/specs/ARB/draw_instanced.txt

Edit. Bah beaten, some older drivers will have it as an EXT extension rather than ARB as well.

Thank you very much for the info.