As a result of the GLES specifications being vague about best practice for how buffers should be used dynamically, different GPUs / platforms appear to have different preferences.
Mac in particular seems to have a number of problems in this area, and none of the rendering team uses Macs. So far we have relied on guesswork to choose the best usage, but in an attempt to pin this down, this PR begins to introduce manual selection of options for users to test their configurations.
Due to my less than eagle-like view over these functions I had assumed they were passing in a single buffer input for the changes to make buffer uploading more efficient. They aren't, which is less than ideal.
So these particular changes should be reverted. When I have some more time I'll see whether the API for these calls can be changed, because as is the multiple glSubBufferData calls could be causing stalls on some hardware.
This is part of effort to make more efficient use of the API for devices with poor drivers. This eliminates multiple calls to glBufferSubData per update.
Batching is mostly separated into a common template which can be used with multiple backends (GLES2 and GLES3 here). Only necessary specifics are in the backend files.
Batching is extended to cover more primitives.
