[osg-users] OpenSceneGraph/osgEarth vs VulkanSceneGraph/vsgpagedlod

[Robert Osfield]

Hi Jason,

On Wed, 24 Mar 2021 at 15:22, Jason Beverage <jasonbeverage at gmail.com>
wrote:

> Very impressive Robert!  As you said, comparing osgEarth to your example
> isn't exactly apples to apples since the implementation under the hood is
> quite different but this is still great.
>

Thanks.  Indeed it's apples to oranges comparison so we shouldn't draw too
many conclusions.  I guess I could rewrite the vsgpagedlod example into an
OSG equivalent so all the settings are the same.  I'd actually be quite a
nice OSG examp[le.  My priority for the OSG is support so I'll have to
leave this to others.


> From what I've seen from your performance reporting, vsg is significantly
> faster than osg in most of your tests.  Do you have a feel for how much of
> that is just Vulkan being faster than OpenGL vs some of the other
> improvements you've made in design decisions of VSG vs OSG?  Are there any
> opportunities for porting some of the structures or concepts from VSG back
> to OSG to get some of the performance benefits you've seen in VSG in OSG?
>

The CPU overhead is much lower in the VSG than the OSG due to architecture
changes in the core Object/Node structure to reduce memory
footprint/bandwidth load and to avoid conditionals, These could be ported
into an OSG lite, but it'd break compatibility with a great many
applications - no BoundingSphere on all nodes, no NodeMask, no Callbacks,
no ancillary data stored in Object/Node.  It would break so many
applications and even the OSG itself it wouldn't be a small task to update
everything.

The differences are fundamental to the VSG delivering on the performance
capability that Vulkan provides, without it you'd only see a small %
improvement here or there if porting the OSG from OpenGL to Vulkan.  I've a
few applications and libraries that cite modest improvements when porting
to Vulkan, and don't recall any that claim 3 x to 10+ x faster than I'm
seeing on OSG vs VSG.  I think this either means the OSG is more of CPU hog
that we've long assumed or the VSG does a better job of not holding Vulkan
back by designing everything from the ground up to not get in the way as
much as possible.  I suspect it's a bit of both.

 Cheers,
Robert.

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