Thanks Robert,
It works for me. I will do more testing later today. I will let you know if I
find some problem.
I have one bit nosy question though. It looks like Polytope::contains methods
always initialize _resultMask to parent clipping mask (_maskStack.back() ) and
then compute updated clipping result for child node/drawable. If its true, then
resultMask for a child is always smaller or equal to resultMask of parent. So
it looks like condition:
if ( frustum.getCurrentMask() && frustum.getResultMask() )
in CullVisitor.cpp updateCalculatedNearFar line 607 is bit redundant and
could be replaced with simpler check:
if ( frustum.getResultMask() )
Am I right ? I suppose that former construct was somehow caused by the bug we
just fixed.
Cheers,
Wojtek Lewandowski
----- Original Message -----
From: "Robert Osfield" <[email protected]>
To: "OpenSceneGraph Submissions" <[email protected]>
Sent: Thursday, May 07, 2009 8:34 PM
Subject: Re: [osg-submissions] Bug in near plane computations
Hi Wojtek,
I've done a bit of testing and review of the code and feel the most
apprioriate change of for setupMask to use push_back() rather than a
back() assignment. I've been testing various models and your one and
they all seem to hang together with this change.
Could you test svn/trunk and let me know how you get on.
Cheers,
Robert.
2009/5/6 Wojciech Lewandowski <[email protected]>:
> Hi Robert,
>
> We noticed an issue with COMPUTE_NEAR_FAR_USING_PRIMITIVES mode. I have
> prepared simplified .osg example scene which shows the problem. File could
> be tested with slightly modified osgviewer. Modification is required to turn
> on proper near/far mode. Adding following line does this:
>
> viewer
>
> .getCamera()->setComputeNearFarMode(
> osg::Camera::COMPUTE_NEAR_FAR_USING_PRIMITIVES );
> Once loaded into viewer simply move camera forward and you will notice
> that bottom triangle dissapear and notification message is printed in
> console. Message warns about negative near plane candiate which is rejected
> by CullVisitor. 4:3 frustum proportons are important here and its
> neccessary to run in one screen. If run on two screens (8:3) problem does
> not show.
>
> Example file contains two geodes, each with one drawable, stored in two
> branches with pair of Transforms as root and parent of first geode. One of
> these drawables is sphere and second is very sharp long triangle (selection
> of drawables is not really imporant) It turns out that when code fails, near
> plane is computed based on distance to far located sphere instead of much
> closer triangle.
>
> I investigated this case and noticed that problem is related to cliping
> plane mask stack management by CullVisitor frustum. It happens when
> osg::Polytope::_resultMask (mask which stores bits corresponding to clipping
> planes intersecting node/drawable) is not restored after traversal to first
> subbranch of scene tree. When cull traversing next subbranch, call to
> push clipping mask on the mask stack pushes empty mask and consecutive
> culling of drawable assumes that drawable entirely fits into viewing frustum
> which in turn causes above computation error and message warning.
>
> I am sending modified osg/Polytope include file. There are actually two
> places where I changed the code. I am leaving it to your judgment which one
> is better. It may be reasonable to appy them both if they don't break some
> other OSG code.
>
> Problem with selecting proper fix is that I am not sure where the source of
> the problem actually is. There seems to be design assumption that _maskStack
> cannot be empty as all osg::Polytope::contains() methods call
> _maskStack.back() without any checks. But usually when cull traversal starts
> it is initially empty. Code works (most of the time) beacause _maskStack is
> based on fast_back_stack template which always have _value field accesible
> using fast_back_stack::back() method. While it does not produce sig_fault,
> it can return random values when maskStack is not initialized.
> osg::Polytope::setupMask() method overcomes this problem by direct
> assignment of initial clipping mask to _maskStack.back(). But as the above
> example shows this _maskStack.back() will be lost when some action
> in CullVisitor changes _resultMask between pushCurrentMask/popCurrentMask
> combo calls.
>
> Cheers,
> Wojtek Lewandowski
>
> _______________________________________________
> osg-submissions mailing list
> [email protected]
> http://lists.openscenegraph.org/listinfo.cgi/osg-submissions-openscenegraph.org
>
>
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