Hello,
firstly, I have the document "OpenSG: Basic Concepts",
which is from 2002. Is there a newer version of that
paper and where can I find it?
Secondly, I saw that the features list at OpenSG.org
where it says "State Sorting: To efficiently use
graphics hardware, the OpenGL state has to be changed
as rarely as possible. Sorting the visible objects by
state is the main way to do that."
If I take a look at OSGRenderAction.cpp, I can't see
that. I understand that the following is going on:
RenderAction traverses the scenegraph to build its
drawtree. Functors and geometries are dropped in
according to the traversal order. If their material
already exists in a map, the new drawtreenode is
simply <u>appended</u> to the node list of the
material.
When the frame is rendered, State::changeFrom is used;
but the order in which the states come in still
depends on the order the drawtreenodes have been
appended in the drop* methods (and yes, the sort key,
which has to be explicitly set by the user).
In other words: I have two material instances A and B
which produce exactly the same state, but A is used in
a geometry somewhere where the traversal arrives
quickly and B somewhere where the traversal arrives at
the end. Additionally A was the first material ever
created, then a thousand others, then B, so they will
probably not lie beside each other in the material
map, which is apparently sorted by addresses. Then the
rendering of A objects happens a long time before that
of B objects, altough their states are exactly the
same.
Am I missing a point? Maybe I do not correctly
understand the wording of the feature phrase.
Björn
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