Re: [Hgengine-devs] opengl profile

[Charles L. <ch...@cn...>]

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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