Some drivers (at least the Intel drivers on Windows) are slow at
incrementally updating a VBO with hundreds of calls to glBufferSubData
every frame. Performance is significantly better if you use
glBufferData(NULL) to tell it to discard all the previous contents, and
then re-upload all the data at once.
Update CVertexBuffer so that GL_DYNAMIC_DRAW/GL_STREAM_DRAW buffers are
handled with the new mechanism. This requires the caller to hold onto
the backing store so it can be re-uploaded when necessary, and needs a
bit more signalling to indicate exactly what needs uploading.
I see an improvement from roughly 60 to 75 fps on Intel HD Graphics
3000, Windows, 1024x768, Siwa Oasis.
This was SVN commit r16241.
Ykkrosh
0ef6c7555e