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

[Robert Osfield]

Hi All,

Over the past 2 1/2 years I've been mainly focused on VulkanSceneGraph 
project, this isn't yet at 1.0 but it's come along nicely.  This week I 
wrote an example that illustrates how to use vsg::PagedLOD and 
vsg::ReaderWriter to implement paged database that streams data from online 
tile serves such a OpenStreetMap and ReadyMap.  It's like a very simple and 
crude demo of osgEarth style paging.

To look at the visual differences and performance differences I've recorded 
a camera animation path in osgviewer then run this same path with the same 
OpenStreetMap databasee in osgviewer using osgEarth, and then with the same 
path but using the new vsgpagedlod example. 

    
https://github.com/vsg-dev/vsgExamples/tree/PagedLOD/examples/nodes/vsgpagedlod

I've upload the a video of running the two applications, first the OSG then 
VSG, to youtube:

    https://www.youtube.com/watch?v=nOQxr09ald4

The average fps for the 2 minutes camera animation path was 878fps for the 
OSG/osgEarth combo and 2698fps for VSG/vsgpagedlod, which is just under 3 
times faster for the Vulkan/VulkanSceneGraph.

As I explain in the video it's not an exact like for like comparison as 
osgEarth is doing blending between LODs, while the VSG/vsgpagedlod is 
selecting a higher level of detail for a given view.

The osgviewer was run with default DrawThreadPerContext threading, while 
vsgpagedlod viewer was running single threaded.  In both cases the 
osgDB::DatabasePager and equivalent vsg::DatabasePager are doing all the 
loading in a set of background threads.

The VSG supports running viewer multi-threaded but is unnecessary in this 
instance as the cull/draw traversal/dispatch are all happening less than 
half a millisecond :-)

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