Hi Robert,
My scene is already a quad tree. Anyway, most of the time,
all the objects are visible.
So the only thing I can do is duplicate the object instances,
flatten transform nodes and merge the resulting geometries.
The simulation use a huge paged terrain. I have two options:
- pre-process the dropped objects -> decrease paging performances
- defer the optimization in the terrain tile loading -> cost ?
Does the database paging has been optimized or modified when the
new threading model has been coded ?
Robert Osfield wrote:
Hi Lionel,
MatrixTransform are relatively expensive on cull and draw so best used
sparingly. The osgUtil::Optimizer has a FlattenStaticTransform to
help apply transforms down onto the geometry below them to avoid this
cost.
The other thing to do make sure you have a well balanced scene graph -
one that has a quad tree hierarchy of group nodes as this helps
accelerate the cull traversal, as flat scene graphs where one group
contains hundreds of children doesn't allow for high level view
frustum culling - the aim should always try to cull as high up in the
scene graph as possible.
The granularity of your scene graph is something else you can look at,
at scene graph that is too fine grained will be expensive on cull and
draw. Clumping local geometry together into a single osg::Geometry
can help tremendously. Using texture atlas' can help enable the
combining of separate geometries together. In SVN there is a new
texture atlas build which is part of the Optimizer.
Other trick you can deploy with the SVN version is to use the
osgViewer::Viewer's ability to thread cull and draw separately by
double buffering the rendering back end. Look for the discussion of
DrawThreadPerContext on osg-users over the last few months.
Robert.
On 4/3/07, Lionel Lagarde <[EMAIL PROTECTED]> wrote:
Hi,
While examining our simulation statistics, it appears that the main
bottleneck it the culling stage.
Our simulation data is composed of a terrain covered with objects
(houses,
individual trees, street lamp, ...).
There is a lot of dropped objects (25000 for 16x16 km).
Without these objects, the simulation runs at >300 fps. With the
objects,
the frame rate drop to <30 fps and the cull stage takes 50% of the
frame
rendering time.
My question is: is there a way to improve the culling performances ?
Every dropped object is made of a MatrixTransform and a ProxyNode
(resolved
at loading stage).
The osgforest example shows that the MatrixTransforms aren't good
for culling performances. Removes the transform nodes means to
duplicate the external references. We can do that for low poly
objects (like X trees) but not for all the objects.
Profiling the application shows that the culling stage performances
are bound to:
- the number of transform nodes (because the polytope is rebuilt for
each
node)
- the number of drawables
Is it possible to cache the render leaves of the drawables (some
kind of
cull
callback that attach the precomputed render leaf to the current
render bin)
?
Does someone has tried to do that ?
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