When writing the Quick Start Guide, I opted to err on the side of conservatism. So, if you only modify STATIC scene graph nodes during update(), you can be assured that is a safe operation, and will almost certainly be a safe operation in future OSG releases. In the current incarnation of OSG, however, it's safe to modify STATIC nodes anytime you're not inside cull/draw. Furthermore, you can even modify nodes that are DYNAMIC while you're in the draw() traversal. This is a) more advanced stuff, and b) possibly subject to change in future OSG releases. -Paul
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Himar Carmona Sent: Tuesday, July 03, 2007 6:37 PM To: osg users Subject: [osg-users] Rendering threads and scene graph updates. Hi, i'm working with OSG on Windows. I'm designing a Geo viewer that use OSG internally for rendering purposes, and i have some questions about how the modification of the scene graph must be done to be safe with the cull and draw traversals. After reading the Quick Start Guide and the DatabasePager code and looking at the osg mail archive, what i've found so far is that it is possible to modify the scene graph inside an update callback and that it is the recommended approach (viewer seems to treat databasePager as a special case and don't use update callback). I'm right with that or have i misunderstood something? Until now i have been working with a render thread that i start after the window is created. But after reading a comment in the checkevents method of GraphicsWindowWin32 that says it must be called from the main thread and knowing that Win32 don't like much that different threads access the message loop (as checkevents does), i'm thinking about the possibilty of doing the render from the main thread ( e.g. using WM_TIMER and calling viewer::frame() , i don't have access to the app message loop). Is this possible? The examples i have seen so far use either a render thread (osgviewerMFC) or a custom message loop (osgViewerGLUT). I'm seeking for the possibility of avoiding to implement a custom Update Callback for doing the updates of the scenegraph, and make the changes directly to the scenegraph. It will free me for implementing the changes queues in the update callback (a solution mentioned in a two years old osg mail message) and will simplify my design greatly. The Quick Start Guide mentioned that this is possible, but also mentioned that this requires modifications to the main rendering loop. What else have to be keep in mind? Thanks in advance, Himar.
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