Re: [Hgengine-devs] opengl profile

[Josh <axl...@gm...>]

Yes these improvements will only help with CPU bottlenecks.
But I think there are many things that can be done to make much smarter 
use of opengl.  I would much rather see a GPU bottleneck at this point.  
There are a lot of things that the CPU is not doing at this point 
(sound, physics, animations) which will be taking up time later.

Josh


Charles Lohr wrote:
> I've just examined some changes when it comes to putting the burden on
> the GPU and not.  Reducing the quantity of certain calls, like
> glLoadMatrix(...) did not seem to affect the performance at all when the
> GPU was under load, however had a significant improvement when I shifted
> the CPU back to being the bottleneck.
>
> 472 -> 472
> 772 -> 868
>
> In order to reduce the overhead, I made the system only load the matrix
> and update the shader if the specific node had children.  Otherwise, it
> just keeps going.
>
> This indicates to me that some (possibly many) of the OpenGL functions
> we thought may have had something to do with stealing cycles from the
> GPU, do not, that it is possible there may be another level of
> pipelining going on here that we don't understand.
>
> Additionally, I feel as though we shouldn't strive excessively hard to
> speed up the CPU if that's not the bottleneck, but the fact is, that in
> the end, we should strive to make it as fast as possible because there
> are always portions where it won't be the GPU that's bottlenecked, and
> will in fact be the GPU waiting on the CPU.  The two systems cannot be
> totally decoupled.  I feel we can learn a lot by examining the
> performance changes both under GPU bottleneck (Window at 640x480) and
> CPU bottleneck (Window at 50x50 or less).
>
> Sadly, I'm not sure how much we can push this, since we've seen examples
> where doing more work can result in a higher framerate.
>
> Charles
>
>
> Josh wrote:
>   
>> Attached is a count of opengl API calls for a scene where most things
>> are culled.
>> I will be figuring out how to make this more efficient.
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