Re: [Flightgear-devel] Memory issues

[Tim M. <tim...@gm...>]

On Mon, Aug 13, 2012 at 7:40 PM, James Turner <zak...@ma...> wrote:
>
> On 11 Aug 2012, at 18:21, Tim Moore wrote:
>
>> This is what osg::PagedLOD does, though we often forget that the
>> paging of the higher LODs is triggered in the cull phase.
>>> I can't recall what scene modifications are / are not permitted inside a cull-callbacl, however.
>> You would want to let the OSG loader mechanism and the database pager
>> do their thing. Geometry doesn't have to be loaded from files...
>
> Could you outline the pieces of machinery needed for this to work? Given that we already create LOD nodes, I assume it's switching those to be PagedLOD, and setting the filename / extension / reader-writerOptions to some magic, and creating a loader which matches that, which creates the buildings geometry.
That is how PagedLODs work, without too much magic. Some data will
need to be passed to the loader. A low-tech way to do that is to
encode parameters in the "file name" passed to the loader, but in this
case you will probably need access to the scenery to place buildings.
You can subclass the DatabaseOptions object stored in the PagedLOD to
store whatever you need.

You would choose a file extension that doesn't correspond to a real
file type, and then register a loader with that extension.
>
> If you could point to an example of such a loader, I'm pretty sure Stuart or I could adapt his code.
>
> James

We register loading callbacks using both osgDB mechanisms and some
SimGear goo to control optimizations, construction bvh trees, etc.
grep for ModelRegistryCallbackProxy. For the body of the loader, there
is nothing special; just don't  read any files.

Tim
>
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