[osg-users] PagedLOD glitches

[Andreas Ekstrand]

Hi Robert,

The glitches are purely visual. I have no overlapping ranges, my problem 
is the opposite - when I'm moving towards a level and the range 
switches, it takes a while to load the high level and the low level is 
switched off. While loading, there is just empty space for a while until 
the high level has been loaded and is visualized.

Attached is an attempt to illustrate the problem. When moving from 
position 1 to 2, the middle level is switched out and although the high 
level is within its range it takes a while to load it, so there is a 
hole until it's finally been loaded in 3. Note that I don't have to move 
the viewer between 2 and 3, just wait for the loading. I would want the 
middle level to be visible until the high level is actually loaded.

Maybe I'm misunderstanding something about PagedLOD, the database pager, 
or how to create quad-tree scene graphs for it to work properly? I have 
only developed these things myself before in other projects, and 
actually not used PagedLOD until now.

Regards,
Andreas


On 2016-08-26 15:58, Robert Osfield wrote:
> Hi Andreas,
>
> On 26 August 2016 at 12:09, Andreas Ekstrand
> <andreas.ekstrand at remograph.com> wrote:
>> Is there any way to avoid glitches in the PagedLOD during loading of the
>> higher level after the lower level has switched out?
> Are we talking just a visual glitch or a frame rate drop, or both?
>
>> When flying over my
>> quad-tree terrain the tiles are flickering and the background color is
>> visible a short while before the higher level has been loaded.
>>
>> One can of course override and implement logic that waits to switch the
>> lower level of until the higher has been loaded, but maybe I have missed
>> some existing setting?
> The logic in PageLOD::traverse() that decides between which LOD's to
> display depends entirely on the LOD ranges used for each child, if the
> ranges are distinct then no two children of a single PageLOD will be
> displayed at the same time.
>
> If you built the database such that the PageLOD's overlap a bit then
> you have a case where both a lower level of detail and higher level of
> detail could be visible at once.  Given your description this sounds
> like it may be possibility.  I wouldn't recommend building PageLOD
> databases with overlapping LOD range though - they can abut but
> shouldn't overlap.
>
> The other possibility might be display latency, or if you have some
> kinds of higher level effect for visually blending between LOD levels.
>
> Robert.
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>

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