Documented all functions, adding use case and side effects.
Also replace the use of shortened argument name by more meaningful ones.
Renamed `GPU_batch_instbuf_add_ex` and `GPU_batch_vertbuf_add_ex` to remove
the `ex` suffix as they are the main version used (removed the few usage
of the other version).
Renamed `GPU_batch_draw_instanced` to `GPU_batch_draw_instance_range` and
make it consistent with `GPU_batch_draw_range`.
The goal is to improve clarity and readability, without
introducing big design changes.
Follows the recent obmat to object_to_world refactor: the
similar naming is used, and it is a run-time only rename,
meaning, there is no affect on .blend files.
This patch does not touch the redundant inversions. Those
can be removed in almost (if not all) cases, but it would
be the best to do it as a separate change.
Differential Revision: https://developer.blender.org/D16367
This was because `stroke_id` was not using `vertex_start`.
But since `vertex_start` is not 1 based like it used to be, we need to add
1 to it to avoid a fragment depth of `0.0` which would be equal to the
background and not render.
