Re: [osg-users] Polytope from view frustum

[Glenn Waldron]

Also check out osgShadow::ConvexPolyhedron if you want to extract the
corner verts or make geometry from it.



Glenn Waldron

On Wed, Nov 2, 2016 at 9:47 AM, Jeff Biggs  wrote:

>
> try this...
>
> osg::Polytope GetViewPolytope(
> const osg::Matrix ,
> const osg::Matrix ,
> const osg::Matrix )
> {
> osg::Polytope clipspace;
> clipspace.setToUnitFrustum(true, true);
>
> // composite matrix
> osg::Matrixd mvp = m * v * p;
>
> // transform from clip space to local coords
> osg::Polytope local;
> local.setAndTransformProvidingInverse(clipspace, mvp);
>
> return local;
> }
>
> // --- Sample use case ---
>
> osg::Camera *cam;
> osg::Matrixd entityBodyMatrix;
>
> osg::Polytope viewPolytope = GetViewPolytope(
> cam->getProjectionMatrix(), cam->getViewMatrix(), entityBodyMatrix);
>
> const osg::BoundingSphere boundSphere;
>
> if (viewPolytope.contains(boundSphere) {
> // sphere is inside of view
> }
>
> jeff
>
>
>
> On 11/2/16 3:43 AM, Robert Osfield wrote:
>
>> On 1 November 2016 at 21:45, Trajce Nikolov NICK
>>  wrote:
>>
>>> Hi Community,
>>>
>>> anyone knowing how to achieve this and with will to share?
>>>
>>> Thanks a bunch as always !!
>>>
>> Have a look at the API's...
>>
>> First one to look at is osg::Polytope, create one of these with a unit
>> frustum.  This will be in clip space.
>>
>> Next step transform this Polytope by the projection matrix using the
>> transformProvidingInverse() method (to transform a plane you multiple
>> it by the inverse of that matrix), so in our case the projection
>> matrix transform from eye space into clip space which is the inverse
>> of the transform we intend, but thanks to the way that planes are
>> transformed we can just use the projection matrix directly as long as
>> we use the transformProvidingInverse().  See the src/osg/CullStack.cpp
>> to see this in action.
>>
>> Then transform into object coordinates using the same method by
>> providing the view and model matrices.
>>
>> Robert.
>> ___
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>>
>>
>>
>
> --
> Jeff Biggs
>
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Re: [osg-users] Polytope from view frustum

[Jeff Biggs]

try this...

osg::Polytope GetViewPolytope(
const osg::Matrix ,
const osg::Matrix ,
const osg::Matrix )
{
osg::Polytope clipspace;
clipspace.setToUnitFrustum(true, true);

// composite matrix
osg::Matrixd mvp = m * v * p;

// transform from clip space to local coords
osg::Polytope local;
local.setAndTransformProvidingInverse(clipspace, mvp);

return local;
}

// --- Sample use case ---

osg::Camera *cam;
osg::Matrixd entityBodyMatrix;

osg::Polytope viewPolytope = GetViewPolytope(
cam->getProjectionMatrix(), cam->getViewMatrix(), entityBodyMatrix);

const osg::BoundingSphere boundSphere;

if (viewPolytope.contains(boundSphere) {
// sphere is inside of view
}

jeff



On 11/2/16 3:43 AM, Robert Osfield wrote:

On 1 November 2016 at 21:45, Trajce Nikolov NICK
 wrote:

Hi Community,

anyone knowing how to achieve this and with will to share?

Thanks a bunch as always !!

Have a look at the API's...

First one to look at is osg::Polytope, create one of these with a unit
frustum.  This will be in clip space.

Next step transform this Polytope by the projection matrix using the
transformProvidingInverse() method (to transform a plane you multiple
it by the inverse of that matrix), so in our case the projection
matrix transform from eye space into clip space which is the inverse
of the transform we intend, but thanks to the way that planes are
transformed we can just use the projection matrix directly as long as
we use the transformProvidingInverse().  See the src/osg/CullStack.cpp
to see this in action.

Then transform into object coordinates using the same method by
providing the view and model matrices.

Robert.
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Re: [osg-users] Polytope from view frustum

[Trajce Nikolov NICK]

Thanks Robert

On Wed, Nov 2, 2016 at 9:43 AM, Robert Osfield 
wrote:

> On 1 November 2016 at 21:45, Trajce Nikolov NICK
>  wrote:
> > Hi Community,
> >
> > anyone knowing how to achieve this and with will to share?
> >
> > Thanks a bunch as always !!
>
> Have a look at the API's...
>
> First one to look at is osg::Polytope, create one of these with a unit
> frustum.  This will be in clip space.
>
> Next step transform this Polytope by the projection matrix using the
> transformProvidingInverse() method (to transform a plane you multiple
> it by the inverse of that matrix), so in our case the projection
> matrix transform from eye space into clip space which is the inverse
> of the transform we intend, but thanks to the way that planes are
> transformed we can just use the projection matrix directly as long as
> we use the transformProvidingInverse().  See the src/osg/CullStack.cpp
> to see this in action.
>
> Then transform into object coordinates using the same method by
> providing the view and model matrices.
>
> Robert.
> ___
> osg-users mailing list
> osg-users@lists.openscenegraph.org
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>



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Re: [osg-users] Polytope from view frustum

[Robert Osfield]

On 1 November 2016 at 21:45, Trajce Nikolov NICK
 wrote:
> Hi Community,
>
> anyone knowing how to achieve this and with will to share?
>
> Thanks a bunch as always !!

Have a look at the API's...

First one to look at is osg::Polytope, create one of these with a unit
frustum.  This will be in clip space.

Next step transform this Polytope by the projection matrix using the
transformProvidingInverse() method (to transform a plane you multiple
it by the inverse of that matrix), so in our case the projection
matrix transform from eye space into clip space which is the inverse
of the transform we intend, but thanks to the way that planes are
transformed we can just use the projection matrix directly as long as
we use the transformProvidingInverse().  See the src/osg/CullStack.cpp
to see this in action.

Then transform into object coordinates using the same method by
providing the view and model matrices.

Robert.
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[osg-users] Polytope from view frustum

[Trajce Nikolov NICK]

Hi Community,

anyone knowing how to achieve this and with will to share?

Thanks a bunch as always !!

Cheers,
Nick

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Re: [osg-users] Polytope - Intersections sorted by distance of localIntersectionPoint and the reference plane

[Ron Mayer]

Hi again,

After thinking about it here is what I think the answer is.
Let's say our polytope intersects two circles (or rectangles) A and B, each at 
two points
A1, A2 and
B1, B2

The center point of A1 and A2 is computed, denote by centerA12
The center point of B1 and B2 is computed, denote by centerB12

Then the distance is measured from centerA12, and centerB12 to the reference 
plane. By default the reference plane is the last plane in teh polytope - 
meaning, if the polytope is made out of 5 half-planes, the last one is the 
default reference plane (the last one, as the last one in the data structure 
the half-planes are stored).

The polytope intersector then stores the nodes sorted by the distance as 
described above.

Still need to understand what happens if one of the circles is completely 
inside the polytope, what is the order of such an object in the sorting scheme. 

Also, another question I was asking myself, was about duplicate reporting.
Let's say I have a parent and a child node both at the same location.
When the polytope intersector intersects both, are they reported as 2 different 
intersections (each having their own path, which is the same except of one 
node)? (I would say yes)

Cheers,
Ron

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[osg-users] Polytope - Intersections sorted by distance of localIntersectionPoint and the reference plane

[Ron Mayer]

Hi,

I am trying to understand what are
(1) distance of the localIntersectionPoint, (2) the reference plane in a 
polytope intersector, and (3) last plane of the polytope, which are used to 
sort the intersections of a Polytope intersector.

I know that a volume is created with half-planes in a polygon shape for the 
intersection volume, then the scene nodes are tested to see if they are inside 
or intersect the polytope (or outside).
During this process, a list of intersections is created sorted by the distance 
of the localIntersectionPoint and the reference plane.
also
The default for the reference plane is the last plane of the polytope

Can someone give an explanation about these?  (or explain through an example 
of, let's say, 2 lines intersecting a polytope, how will they be sorted?)

Cheers,
Ron

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[osg-users] Polytope

[Peter Wraae Marino]

Hi,

I just started to use the polytope and polytopeintersect and have some  results 
I did not expect.

In the code there are 3 cases that creates an osg::Box which is the cube I want 
to intersect with the plane. The 3 cases have each a different solution, where 
I expect them all to have the same solution which is 4 intersections. There is 
a comment next to each osg::Box being created.. can someone explain to me why I 
don't get 4 intersections in all cases? the only difference in each case is 
that I create the box in a different location.

here is the code:


Code:

#include stdafx.h
#include osg/group
#include osg/geometry
#include osgViewer/Viewer
#include osg/Polytope
#include osg/ShapeDrawable
#include osgUtil/PolytopeIntersector
#include osg/shape
#include iostream

osg::Group* createScene()
{
osg::Group* root = new osg::Group;

// create group for objects we want to collide against
osg::Group* pGroup = new osg::Group;
root-addChild( pGroup );

osg::Geometry* pTest = osg::createTexturedQuadGeometry( 
osg::Vec3(-2.0f,-2.0f,0.0), 
osg::Vec3(4.0f,0.0f,0.0), 
osg::Vec3(0.0f,4.0f,0.0f) );
osg::Geode* pGeodeTest = new osg::Geode;
pGeodeTest-addDrawable( pTest );
pGroup-addChild( pGeodeTest );

// create a cube
osg::Geode* pGeode = new osg::Geode;

//osg::ShapeDrawable* pShape = new osg::ShapeDrawable( new 
osg::Box(osg::Vec3(0.0f,0.0f,0.0f),0.2f) );  // 4 intersections, but 2 of them 
in the same place (not expected)
//osg::ShapeDrawable* pShape = new osg::ShapeDrawable( new 
osg::Box(osg::Vec3(0.2f,0.0f,0.0f),0.2f) );  // only two intersections (not 
expected)
osg::ShapeDrawable* pShape = new osg::ShapeDrawable( new 
osg::Box(osg::Vec3(0.5f,0.0f,0.0f),0.2f) );  // 4 intersections (expected)

pShape-setColor( osg::Vec4( 0,1,0,1 ) );
pGeode-addDrawable( pShape );
root-addChild( pGeode );

osg::Polytope* p = new osg::Polytope;
p-setToBoundingBox( pGeode-getBoundingBox() );

osgUtil::PolytopeIntersector* intersector = new 
osgUtil::PolytopeIntersector( osgUtil::Intersector::MODEL, *p );
osgUtil::IntersectionVisitor* iv = new osgUtil::IntersectionVisitor;
iv-setIntersector( intersector );

pGroup-accept( *iv );

if ( iv-getIntersector()-containsIntersections() )
{
std::cout  COUNT:   
intersector-getIntersections().size()  std::endl;
std::cout  FIRST COUNT:   
intersector-getFirstIntersection().numIntersectionPoints  std::endl;

osgUtil::PolytopeIntersector::Intersection firstIntersection = 
intersector-getFirstIntersection();

for ( unsigned int i=0; 
ifirstIntersection.numIntersectionPoints; i++ )
{
osg::Vec3 pos = firstIntersection.intersectionPoints[i];

std::cout  POS   i  :   pos.x()  ,   
pos.y()  ,   pos.z()  std::endl;
std::cout  max dist   
firstIntersection.maxDistance  std::endl;
std::cout  distance   firstIntersection.distance 
 std::endl;

osg::Geode* pGeode = new osg::Geode;
osg::ShapeDrawable* pTestSphere = new 
osg::ShapeDrawable( new osg::Sphere(pos,0.02f) );
pTestSphere-setColor( osg::Vec4(1,0,0,1) );
pGeode-addDrawable( pTestSphere );
root-addChild( pGeode );
}
}

return root;
}

int _tmain(int argc, _TCHAR* argv[])
{
// construct the viewer
osg::ref_ptrosgViewer::Viewer rViewer = new osgViewer::Viewer;

rViewer-setUpViewInWindow( 32, 32, 800, 600 );

rViewer-setSceneData( createScene() );

return rViewer-run();
}






Thank you!

Cheers,
Peter

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[osg-users] Polytope intersector

[Tim Moore]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

 From: Paul Martz [EMAIL PROTECTED]
 Subject: Re: Mouse Picking (again...)
 Newsgroups: gmane.comp.graphics.openscenegraph.user
 Date: 2007-12-13 20:44:13 GMT (5 days, 19 hours and 28 minutes ago)
 
  Here I am, then, asking anyone that can answer me,
 why it didn't work even though I used a box rendered
 vertex by vertex?
 
 There is a known bug with the Polytope intersection class: at least one
 vertex must be in the polytope in order for it to return a hit. If you
 mouse-click in the middle of a quad and no vertices are within the Polytope,
 no pick is returned.
 
 You can test to see if this is the problem by clicking on a corner of your
 box. That should return a pick. (If it doesn't, then you have some other
 bug.)
Is still true? I notice recent work on the PolytopeIntersector, as well as code 
that
seems to specifically address the problem you mention. Note that I'm too lazy 
to check
myself :)

Tim
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