Hi guys,
thanks for all your answers. Unfortunately, I am leaving for a week
holidays in one hour.
Anyway, the problem is following:
- I am generating shadow volumes "on the fly" in cull visitor
- It works perfectly, except the cases when mirrors are used - let's
recall that mirror turns right-handed coordinate system to left-handed,
thus the programmer needs to change FrontFace setting to keep face
culling working properly.
- Ignoring FrontFace settings, I may construct anti-shadow volume that
produces wrong results when mixed with non-anti volumes, etc.
- Moreover, blending and alpha test settings should be detected and
semi-transparent object should not cast shadows. I can detect them
bellow in the scene graph during triangle collecting traversal, but what
about attributes above my shadow node? Ignoring them may result in wrong
results.
I guess, the best solution is to query "current traversal state" for
blending and front face settings. At least that is what I have done in
another scene graph library. Other option is to traverse scene graph up
from my shadowed node to see if there are any attributes important for
myself.
But if there is no nice solution, lets leave the problem. I just wanted
to create complete issue-free solution, as this solution may be
contributed back to OSG one day when stable enough.
John
Wojciech Lewandowski wrote:
Hi John,
If you need this to setup uniforms for shadow fragment shaders then
maybe standard GL gl_FrontFacing variable could do the trick ? Its
available at least in GLSL 1.50 and above. I have not checked when it
was introduced maybe its available in earlier GLSL profiles.
Wojtek
*From:* PCJohn <mailto:[email protected]>
*Sent:* Thursday, August 05, 2010 12:41 AM
*To:* OpenSceneGraph Users <mailto:[email protected]>
*Subject:* Re: [osg-users] threading and captureCurrentState
Yes. There is. Oh. I see. Sorry for confusion, you call it
attribute stack.... and that is a correct name for it.
Anyway, there is State::_attributeMap that is composed of
AttributeStack structs and they have a member attributeVec that
is serving as a stack of attributes. The top of the stack is
"current" attribute or the last pushed attribute. That is the one
I need to get. Until now, I see a threading issue like two
threads manipulating the "attribute stack".
I'll say it again: you can't access those attribute stacks from the
cull traversal. They don't contain anything sensible.
I that case a different question: How to get "current" osg::FrontFace
attribute? I mean the one that would be active for any drawable
traversed at the present moment during cull traversal that is just in
progress and I am handling it in my custom Shadow class that is
already working perfectly except some attribute values that user may
pass from the scene graph above and that need to be properly handled
to cast shadows correctly. The answer: "you do not need it" would be
wrong at the moment.
Thx,
John
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