Your main problem with this code is the way you're updating your VBO. Calling glBufferSubData in this manner is going to lead to pipeline stalls and flushes, and doing it potentially so many times per frame will make things worse. You need to implement proper buffer streaming to get this working well; have a read of this post for a description of the technique.

Sample code:GLuint bufferid;
int buffersize = 0x400000;
int bufferoffset = 0;

void StreamBuffer (void *data, int batchsize)
{
glBindBuffer (GL_ARRAY_BUFFER, bufferid);

if (bufferoffset + batchsize >= buffersize)
{
glBufferData (GL_ARRAY_BUFFER, buffersize, NULL, GL_STREAM_DRAW);
bufferoffset = 0;
}

GLbitfield access = (GL_MAP_WRITE_BIT | GL_MAP_UNSYNCHRONIZED_BIT | GL_MAP_INVALIDATE_RANGE_BIT);
void *mappeddata = glMapBufferRange (GL_ARRAY_BUFFER, bufferoffset, bufferoffset + batchsize, access);

if (mappeddata)
{
memcpy (mappeddata, data, batchsize);
glUnmapBuffer (GL_ARRAY_BUFFER);
glDrawArrays ( .... );
bufferoffset += batchsize;
}
}
Ideally you wouldn't memcpy here; you'd generate the batch data directly into the pointer returned from glMapBufferRange instead. That's not always possible though, and memcpy is fine for many (if not most) use cases - the key is in avoiding pipeline stalls and the CPU-side overhead from memcpy is going to be very low by comparison.

You've pretty much got it, yes. It's really just a simple circular buffer; there's no voodoo in it and the only tricky thing is knowing the correct GL calls to use.

You're going to have some added complexity if you're using separate VBOs for positions and texcoords - I'd recommend that you define a vertex struct containing both and interleave them using a single VBO; it'll perform better and make your code much simpler.

Yes, buffer orphaning is what happens in the first "if" check; there are also flags on glMapBufferRange that you can use to accomplish this, but I prefer to use glBufferData (... NULL, ...) - not for any technical reason, just so that I can more easily add a fallback to glBufferSubData if the MapBufferRange call fails (using the same offset and size params). I omitted that from the sample code I posted just for clarity.

Not sure what you mean by vertex arrays here. Old-style vertex arrays or newer VAOs? If the former, there's no need to do this kind of process - you're using memory owned and managed by your program (rather than by the GPU) so there's no resource contention to speak of, and you don't need anything special to handle it.

You're getting your offsets/etc wrong here - this in particular is not what you want:void* mappedData = glMapBufferRange(GL_ARRAY_BUFFER, m_BufferOffset, m_BufferOffset + currentBatch->spriteCount, access);

I should probably have stated explicitly that the sample code I gave above works in byte sizes, not numbers of vertexes or numbers of sprites, so as a result things need to be adjusted accordingly if you're going to use other units.

So, the second parameter to glMapBufferRange is an offset in bytes, so make it m_BufferOffset * sizeof (MLBatchItem::Vertex) * 4 instead. The third parameter is the size of the range to map (also in bytes), not the end offset of the full range, so it becomes currentBatch->spriteCount * sizeof (MLBatchItem::Vertex) * 4.

You should also make sure that your value of m_BufferSize is equal to (however many sprites fit in your buffer) * sizeof (MLBatchItem::Vertex) * 4; likewise memcpy needs a size in bytes, glDrawArrays takes a number of vertexes, not a number of sprites as it's third param, and your offset needs to be incremented by the number of vertexes, not the number of sprites. There may be a few other places I've missed.