Hi Jimmy,
Regarding of having a flat scene graph. Does it matter if the whole scene will
always be seen? Would it still improve the performance if I balance the scene
graph more?
In the case where the whole scene will always be seen (think about it
carefully, though, because I think these cases should be rare in
practice) then balancing the graph will not help, but removing groups
and transforms will. That is to say, if all your objects will always be
visible, then in order to reduce the cull time you need to reduce the
number of objects to traverse to get to the geometry. To reduce the draw
time, you need to group geometry so that data is uploaded to the card in
good-sized chunks.
So for example, if two objects will always be in the same position
relative to one another, place both in the same osg::Geometry,
transforming the vertices of the second one to be where the transform
would have placed it relative to the first.
Say object 0 has vertex array V0 and object 1 has vertex array V1, and
suppose that object 0 is at world position T0 and object 1 is at
position T1, then you can build a vertex array V2 containing the
vertices of both objects like this:
V2 = (V0, V1 + (T1 - T0))
(suppose the addition above will apply the same translation to all
vertices in V1) and then position the composite object at position T0.
You can extend this if you have groups of many objects that will always
be in the same relative position from each other, of course. For example
if a city has buildings and all the buildings are static in world space,
then place them all in the world coordinate frame with no transforms or
groups. They can still be in different geometry objects if they have a
sufficient number of vertices (thousands). If not, then group several of
them in the same geometry object and use a texture atlas to texture them
all with the same texture file.
Similar scene graph optimization tips have been discussed in the past on
the list. The archives should contain even more tips. I don't know if
there is a wiki page on openscenegraph.org that collects such tips, but
if there isn't we should create one...
Hope this helps,
J-S
--
______________________________________________________
Jean-Sebastien Guay [email protected]
http://www.cm-labs.com/
http://whitestar02.webhop.org/
_______________________________________________
osg-users mailing list
[email protected]
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
