[osg-users] How to reduce the cache size limit of OSG ?

[OpenSceneGraph Users]

Hi Robert,

Sorry for the late reply. The codes of CreateGeometryNode looks like this: 
osg::ref_ptr<osg::MatrixTransform> CreateGeometryNode() {
    std::vector<float> xyzs = RandomPoints(); ///< Create ramdon number of 
points 
    osg::Vec3Array vs = new osg::Vec3Array(xyzs.size()/3, (const osg::Vec3 
*)(xyzs.data()));
    osg::ref_ptr<osg::Geometry> geo = new osg::Geometry;
    geo->setVertexArray(vs.get());
    geo->setColorArray(osg::Vec3(0.5,0.5,0.5));
    geo->setColorBinding(osg::Geometry::BIND_OVERALL);
    geo->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::POINTS, 0, 
numpt));
    geo->getOrCreateStateSet()->setMode(GL_LIGHTING, 
osg::StateAttribute::OFF);
    geo->getOrCreateStateSet()->setAttribute(new osg::Point(size), 
osg::StateAttribute::ON);
    osg::ref_ptr<osg::MatrixTransform> mt = new osg::MatrixTransform;
    osg::ref_ptr<osg::Geode> geode = new osg::Geode;
    geode->addDrawable(geo.get());
    mt->addChild(geode);
    return mt; 
}

There's an old post from you which said that OSG will cache objects to 
improve performance, I wonder if this is the case and how I could change 
that behavior. 

Thanks! 

On Wednesday, May 27, 2020 at 2:37:27 AM UTC+8, Robert Osfield wrote:
>
> Hi Hui,
>
>
> On Tuesday, 26 May 2020 10:36:18 UTC+1, Hui Li wrote:
>>
>>
>> The codes looks like this: 
>> ```
>> root = GroupOfSwitch(); 
>> viewer->setSceneData(root);
>> while (!viewer->done()) {
>>     root->removeChild(0); // Remove the point cloud 
>>     pc = sensor.Capture();  // Get the point cloud
>>     geo = CreateGeometryNode(pc);
>>     root->addChild(geo); // Add the pointcloud 
>>     viewer->frame();
>> }
>>
>>
> In "principle" this shouldn't cause unbounded memory growth but as you 
> don't provide any details about the CreateGeometryNode() there is no way 
> for use know what is going on there.  It could be that your leak it right 
> there in that function call, or else where somewhere in your application.
>
> While I can't comment about the details of your implementation the 
> approach of removing, creating and adding new nodes and associated data 
> each frame is really, really inefficient.
>
> As much as possible you should try to reuse data.  For a point cloud 
> application where the data is dynamic I would personally allocate a fixed 
> number of Geometry nodes with fixed Vec3Array's within them and single 
> DrawArray primitive set.  I'd allocate the Vec3Array to it's full size 
> right up front and next change it's size.  The DrawArrays has a count value 
> that you can set to specify how many vertices in the array need to be 
> rendered and needn't be the whole length of the Vec3Aray.
>
> With really large datasets I would chunk the data so rather one big 
> osg::Geometry, I'd have say 10,000 vertices in each osg::Geometry.  I would 
> also use VertexBufferObjects and avoid using DisplayLists.
>
> Do this all correctly and you should get a good performance and no memory 
> growth.
>
> Robert.
>  
>

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