Hi Torben,
the framecylce consists of 4 parts:
Code:
advance();
eventTraversal();
updateTraversal();
drawTraversal();
What you called "drawTraversal" is actually called
renderingTraversals(), and consists of two phases: the cull phase, where
OSG traverses the scene gathering things it needs to draw into a render
graph, and the draw phase, where it dispatches the draw commands (OpenGL
calls) required to render what is in the render graph.
But you got the high-level idea.
My question:
- The camera manipulators handle(); function is called by the the
eventTraversal, right?
- is the manipulators handle() function called before or after the execution of
the callback function?
- I would like to use the callback to catch some external camera data, then
calculate the camera position/attitude immediately and send thsi resulting camera
modelview to other hosts to apply this camerasetting to their cameras. -> is
it possible only be the viewmatrix or do I have to transfer other data?
From your questions, I think one important fact is missing for you to
understand what's going on: the camera manipulator gets events during
the update traversal, but the view gets the view matrix from it during
the cull traversal.
Essentially, all the camera manipulator does during the event phase is
get events and figure out what it should do with them. The actual
calculation of the view matrix (which is what the camera needs to be
able to position itself in the world) is calculated in the cull
traversal, where the view will do:
if (cameraManipulator.valid())
{
osg::Matrix viewMatrix = cameraManipulator->getInverseMatrix();
camera->setViewMatrix(viewMatrix);
}
// Use the camera's view matrix as the start of the model view matrix.
osg::Matrix modelViewMatrix = camera->getViewMatrix();
// Start accumulating transforms down from the camera to form the
// model view matrix at each node.
// ...
(this is from memory, but you could place a breakpoint in
TrackballManipulator::getInverseMatrix() and go up in the stack trace
when your breakpoint is hit to see the whole code.
The point is, if you have a camera manipulator, it will overwrite
whatever you set as your camera's view matrix in a callback. If you want
to set the camera's view matrix yourself, just don't use a camera
manipulator. As you can see from the code I wrote from memory above, if
the view's cameraManipulator is NULL nothing will touch the values you
set in your camera's view matrix.
Just so you know, calling viewer.run() adds a camera manipulator
(TrackballManipulator) by default. If you do
while (!viewer.done)
viewer.frame();
instead, there won't be a camera manipulator added (you can add the one
you want, a custom one, or none at all).
I tried to get this information directly from the osg sources, but my knowledge
is currently insufficient to unterstand the code at this aspect.. (yes, I'm one
of these guys commenting code not to loose the overview, so I'm struggling at
pure code..)
The code is not the only tool you have to try and understand things...
As I said above, one good way is to set breakpoints and walk through the
code that way.
Hope this helps,
J-S
--
______________________________________________________
Jean-Sebastien Guay jean-sebastien.g...@cm-labs.com
http://www.cm-labs.com/
http://whitestar02.webhop.org/
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