Hi Peter,
This is the problem I am trying to solve:
-------------------------------------------
Two partly transparent polygons intersect each other. Example: A tree created
from two quads. The tree has many pixels that is completely opaque, and many
pixels that is semi visible (transparent) and of course many invisible pixels.
If you render them without writing to the depth buffer:
- One will partly owerwrite the other.
If you render them with writing to the depth buffer:
- One will partly block the other.
Solution:
Render them twice.
First render without writing to the depth buffer.
Second render with writing to the depth buffer.
When you have multiple trees then trees that are close to each other will some
times overwrite or block each others, so I need to solve this too. It can be
solved by rendering all trees in one pass, then all trees again in a second
pass. Rendering each tree independently in two passes will only solve the
problem for that tree while it can still block or overwrite other trees. So I
must render all trees without writing to depth buffer and then all trees again
with writing to depth buffer.
This solution works greatly.
The following is a new problem occurring when I am trying to render parts of
the scene-grapth two times:
--------------------------------------------------------------------------------------------------------
I need to reduce the number of polygons I render twice.
So, all completely opaque polygons need to be rendered only once.
All transparent polygons must be rendered twice.
The node tree is quite complex. It contains many different nodes which are
turned on and off at runtime.
I need to detect who got transparent polygons. This problem is solved by a node
visitor that checks the node's stateset and sees if it contains the BLEND state
turned on.
I can also say that render bin 10 is the only bin that contain transparent
objects.
If I want to go for the group node solution then I need a group that point only
to transparent objects, and another group that point to the same objects. I
then need to render both in one go. Sounds doable, but would be quite messy
when you shall fo example add LOD nodes that contains both transparent and
opaque objects. I would need to split them apart runtime and actually rewrite
the whole tree. I do not think that is doable.
My solution was to mask the nodes so that I could use the cullMask on the
camera to decide wether I want to render opaque objects or transparent objects.
So I can have 3 cameras.
First one render opaque.
2nd renders transparent without depth write.
3rd renders transparent again with depth write.
The solution works like a dream this far.
So what is the real problem?
If someone add anything to the node tree, then I need to pre-process the nodes
and set nodeMasks on them.
I can as you suggest write an interface function that all of our code must use
to add nodes to the tree. It would work nicely.
Any future code will then be dependent on my library. Not a high price to pay.
Any future 3rd party products we use will also have to use my add function.
This may cost more. If the products create a sub-tree which it give back to me
then I can add it through the function. If the product later on through OSG
callbacks decide to add more nodes then I have a huge problem. They would not
use my function and would proably have 0xffffffff as node mask which means they
would be rendered one time per camera I use.
So... I am struggeling to avoid this function. If I can somehow know that
something is added to the tree, then I can simply re-format the tree. Any
future products will therefore work automatically and no human errors can break
the system.
Sorry for writing such a large mail, but its hard to explain with letters :-) I
hope it clearifies my problem.
Cheers,
Viggo
Date: Wed, 23 Jul 2008 15:10:45 +0200From: [EMAIL PROTECTED]: [EMAIL
PROTECTED]: Re: [osg-users] Is it possible to know when the node-graph is
'dirty'?
Hi Viggo,
This is only a suggestion (you may have other reasons). To avoid the human
error as you called it, meaning that if someone forgets to call the reformat
code...
then you should have a method that 3rd party code/humans must use when adding
to your scene, for example
void CMySceneManagerThingy::AddToScene( osg::Node* pNode )
{
// add to wherever you want the pNode to be added in the scene
<code here>
// reformat your scene as you want
<code here>
}on the other subject about rendering multitimes the same object.. you should
just create a new group and add your objects to that group
and the group to the scene (do this as many times as you want)..
don't know why you should be messing around with the renderbins? unless you are
trying somekind of render pass?
regards,
Peter
http://osghelp.com
On Wed, Jul 23, 2008 at 11:00 AM, Viggo Løvli <[EMAIL PROTECTED]> wrote:
Hi Peter, What you say is true in most cases. The 'simplest' way to do this
would be to tell my system that the node-tree need re-formatting each time we
call OSG to add children. That would require two calls each time, and also
requre humans to remember to implement both calls. This opens for human errors,
which at least I dont want (I am lazy).I want to make my module (the one that
need to format the node-masks) independent of the rest of the system, and to
ensure that the rest of the system will not need to know about my module.I also
want to be able to add 3rd party libraries to my application without re-writing
them to do special calls to my module when they add nodes to the tree. So, the
conclusion I have is that I need to automatically know when I need to format
the node-masks. The osg::Group has a callback function named
osg::Group::childInserted.I can make my root-node into a sub-class og
osg::Group where I implement the childInserted function. This way I will get a
callback each time someone add nodes to my root-node. If a module create it's
own osg::Group and add children to it dymically then I would not know anything
about that. I also saw Roberts reply and I agree that a dirty system on the
node-tree would be very expensive. I knew that my question was a longshot. I am
now thinking about other solutions to achieve my goal. The goal is to render
the world with 3 slave cameras. One shall render all render-bins up to bin 9.
One shall render bin 10. And the 3rd shall render bin 10 and up. So bin 10 is
rendered twice. This is to fix some glitches on transparent polygons that
intersect each other while needing to write to the depth-buffer. Ok, so another
solution would be to force a camera to only render a certain number of bins.I
have not seen any place in the code around camera or cull-settings that you can
specify a camera to stay within a limited range of render-bins, so I guess this
won't be as easy either? Do you have any suggestions on how to be able to
render one bin twice in the same frame. The first and second render of the bin
shall have a few render-states set differently. Regards,Viggo
Date: Wed, 23 Jul 2008 07:58:37 +0200From: [EMAIL PROTECTED]: [EMAIL
PROTECTED]: Re: [osg-users] Is it possible to know when the node-graph is
'dirty'?
Hi Viggo,
Don't know the details of your code, but if you are adding a sub-node then you
have code already that is called for adding the sub-node and
thereby you know when the scene-graph has been modified?
regards,
Peter
http://osghelp.com
On Wed, Jul 23, 2008 at 7:51 AM, Viggo Løvli <[EMAIL PROTECTED]> wrote:
Hi, My code is currently formatting the node-masks of the whole scene-graph
before we start rendering. The formatting code is only ran once.If a sub-node
is added to the node-tree afterwards then I want to run my formatting code
again. Is there any way to know whether or not the scene-graph has been
modified? Regards,Viggo
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Regards,Peter Wraae Marinowww.osghelp.com - OpenSceneGraph support site
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