[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 <osg at simperative.com> wrote:

>
> try this...
>
> osg::Polytope GetViewPolytope(
>     const osg::Matrix &p,
>     const osg::Matrix &v,
>     const osg::Matrix &m)
> {
>     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
>> <trajce.nikolov.nick at gmail.com> 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 at lists.openscenegraph.org
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>
>>
>>
>
> --
> Jeff Biggs
>
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>
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