Hi Wojtek, Mixing cull and traversals isn't something I would encourage, it breaks the clean separation of the two operations in a way that limits the types of threading models you can use. Also if the algorithm requires sorting of bins then this can only be done once the whole subgraph has been traversed and all the bins are present.
There are ways and means of mixing things up but it does get really complicated and the solution is likely to be less flexible and less encapsulated - i.e. you'll end with a solution, but not one that can be reused readily. Robert. On Jan 26, 2008 11:06 PM, Wojciech Lewandowski <[EMAIL PROTECTED]> wrote: > > Hi Robert, > > Well maybe I wrote too lengthy explanation for what I am after. I guess it > was bit confusing. > Maybe question should be: is this possible to nest both CULL/DRAW stages for > some prerender camera into my Shadow Map CULL method ? Thats basically what > I would like to do. I know I can insert some aditional CULL traversal of > some subgraph. The question is if I can also DRAW it ? I just want to > prerender a scene to a depth texture/image and analyze it before further > culling (and rendering) the rest of the shadow casting scene ? I am afraid > that OSG does not allow to perform draw stages untill all cameras cull > stages complete. Or does it ? > > Cheers, > Wojtek > > PS: I learned some tricks looking at OverlayNode and even use your > CustomPolytope. But I did not notice nested DRAW stage there. I think I did > good job on computing minimal bounds based on scene traversal and visible > drawable bounding boxes. I am actually scanning render bins after cull > traversal and build bounds around generated render leaves. Then I find > intersection with camera frustum and light frustum. CustomPolytope is good > for that. This method produces small shadow scene bounds when render leaves > (drawables) are much smaller than frustum volume. Unfortuantely my drawables > are quite huge, although also quite sparse. I could try to split them into > smaller chunks, but I don't expect I would be able to "shatter" every > database I get. So I am looking for some worakround for the worst case. > Prerendering and analyzing scene depths is such workaround. I am also trying > to do this because many Shadow Maping papers suggest such aproach for > minimal shadow bounds computation. So out of curiostiy I just want to do > this to get some comparison with scene traversal methods. > > > -----Original Message----- > From: Robert Osfield [mailto:[EMAIL PROTECTED] > Sent: Saturday, January 26, 2008 9:06 PM > To: [EMAIL PROTECTED]; OpenSceneGraph Users > Subject: Re: [osg-users] Scene prerender for selecting parameters needed for > cull and final screen render > > > Hi Wojciech, > > I understand where you are coming from, unfortunately its a pretty > complex topic and one that really needs you to submerge yourself in it > to be able to really understand the issues - it really isn't a topic > that you can dip you toe in and out of. Right now I have another > large task that it is pretty well consuming almost all my time and > intellectual capacity, I'm afraid there is little left for diving into > other meaty topics. > > The best I can do is point you in the direction of work I've done in > the past that comes closest to view dependant render texture work - > and that's in the form of the OverlayNode's > VIEW_DEPENDENT_PERSPECTIVE_OVERLAY. The code in > src/osgSim/OverlayNode.cpp does do some scene traversal to compute a > right bound between the view frustum and the scene. The code isn't > yet producing great results all the time though so it looks like their > or corner cases I haven't accounted for yet, or just some bugs lurking > that I have found. > > As I'm so short on time I can't really dive any deeper than this, good luck, > > Robert. > > On Jan 26, 2008 12:37 PM, Wojciech Lewandowski <[EMAIL PROTECTED]> > wrote: > > Hi Robert, > > > > I am struggling with building decent ShadowMapping approach for flight sim > > application. Due to performance requirements I am hesistant to use > multipass > > PSSM and I am trying to implement (one extra pass only) some kind of > > perspective shadow mapping derived algorithm. I went through Trapezoidal, > > Smallest Bounds, LisPSM. Effective computation of minimal shadow scene > > bounds + LisPSM gave me fairly good results. But this apprach fails when > I > > have badly conditioned database. Few huge drawables that are spread over > > whole terrain kill effectivness of minimal bounds computation. They have > > such big bounds that minimal bound computaion simply does not help at all, > > and I end up using camera frustum as shadow bounds. > > > > So now I am contemplating addition of one prerender pass (ie second extra > > pass ;-( ). This pass would be used for computation of minimal bounds of > > visible scene portion based on an depths rendered to texture. Problem is I > > would like to make this depth analysis pass before actual ShadowMap, Scene > > camera and TexGen setups are done during cull phase. In other words I > would > > like to have the chance to do scene prerender culling and rendering before > > final scene culling and rendering. Is this possible ? Any suggestion for > OSG > > examples to browse ? > > > > Currently my ShadowMap algorithm looks like this (its exactly the same > > control flow as in osgShadow::ShadowMap) > > > > My Shadow Map technique Cull > > Cull Scene Receiving Shadows for final Screen output > render stage > > Find Light source casting shadows > > Compute Bounds of Scene Receiving Shadow visible portion > > Setup Shadow Map camera View and Perspective matrices > > ( based on Scene Bounds and Light source ) > > > > Cull Scene Casting Shadows for Shadow Map prerender stage > > Add shadow coordinates TexGen to final Screen output > render stage > > End My Shadow Map technique Cull > > > > Rendering of RenderStages is executed in following order > > Shadow Map prerender stage > > Final Screen render stage > > > > > > What I would like to achieve looks like this > > > > My next Shadow Map technique Cull > > Cull Scene Receiving Shadows for final Screen output > > Find Light source casting shadows > > > > Depth Analysis prerender pass > > Cull & Render scene producing Depth texture > > ( view and projection are the same as in Scene > Receiving Shadow pass, > > target texture resolution 8x-4x smaller than screen) > > > > Compute Bounds of Scene Receiving Shadows based on image > produced in Depth > > Analysis pass > > Setup Shadow Map camera View and Perspective matrices > > Cull Scene Casting Shadows for Shadow Map prerender > > Setup shadow coordinates TexGen for final Screen output > > End My next Shadow Map technique Cull > > > > Rendering of RenderStages is executed in following order > > Shadow Map prerender stage > > Final Screen render stage > > > > > > Cheers, > > Wojtek > > > > P.S. When I sort all the issues I could contribute some of this work > > (Minimal Bounds Shadow map, LisPSM) to osgShadow portfolio if you are > > interested. > > > > > > > > > > _______________________________________________ > > osg-users mailing list > > osg-users@lists.openscenegraph.org > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
