[osg-users] Qt + non-continuous draw + pagedLOD: Random loss of detail??

John Vidar Larring larring at weatherone.tv
Wed Jul 30 05:39:04 PDT 2008


Hi all,

Background:
-----------
In our application the user can set up scenes ( or sequences as we call 
them) for playback on a timeline (e.g. seq.1 - transition - seg.2 - 
transition ... seq.N). Some scenes are too complex to render real-time 
and are recorded to movies before playback. Hence, when scenes are 
edited by the user all scenes are redrawn as needed rather than 
continuously to avoid sluggish GUI response.

Problem:
--------
_Sometimes_ when the scene is redrawn in edit mode (i.e. redraw only if 
needed), the pagedLOD DB (osgTerrain) drops to the lowest detail level 
(Ref. osg_original.jpg and osg_problem.jpg). This behavior seems to 
appear at randomly. In playback mode (i.e. when frame rate is constant) 
the problem never occurs.

Reproduce / Code example:
----------
The problem has been reproduces in a small test program 
(osgtest_source_code.tgz) derived from the osgviewerQT example (since we 
are using Qt 4.x in our application). To reproduce: run the compiled 
application: 'osgtest -t <your osgTerrain db>' . To trigger refreshes, 
occlude parts of the window with another window. The problem typically 
reveals itself when at a redraw or when the window looses focus (be 
patient, since this happens randomly it may take some time before the 
problem occurs).

Since I'm still quite new to OSG, I'm not sure where to look for a 
solution. Hopefully someone will spot the obvious error in the sample 
code. Any advice is highly appreciated.

Versions:
---------
OSG svn rev 8700
Qt 4.2.3

Best regards,
John Larring

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