Hi Jannik, On 17 August 2016 at 14:52, Jannik Heller <[email protected]> wrote: > I have tested out the VAO branch on my Nvidia graphics card. As you said, > VAO+VBO is slightly faster than VBO but not as fast as display lists. Would > be curious on the performance results with AMD cards. > > Unfortunately, I am unable to use VAO for animated meshes because you've > introduced a new meaning of the dataVariance flag. > https://github.com/openscenegraph/OpenSceneGraph/blob/vertex_array_object/include/osg/Drawable#L523
I haven't introduced a new meaning to DataVariance, all I have done it utilize it for knowing whether the VAO needs updating or not. I have done this to avoid the extra checks required against the individual arrays to see if they are dirty or not - I have done it for performance reasons as I want to keep the CPU overhead for draw dispatch as low as possible. > I do *not* set the dataVariance to DYNAMIC for all my animated meshes because > the performance overhead of DYNAMIC is not acceptable for me. If Drawables > are set to DYNAMIC, OSG would not break frame until all the draws are > submitted. I manage the updates using a double buffering scheme that prevents > the buffer from being modified while the draw thread is using it. So > essentially I don't need the DYNAMIC flag, but now I'm forced to use it (and > incur the performance overhead associated with it) because OSG won't update > the arrays if I don't. :( Previously it was sufficient to dirty() the vertex > arrays to get OSG to update things. Hopefully that can be fixed. This is a sticky one. Your mesh *is* dynamic, the correct way to label the geometry is DYNAMIC. In your usage case you are taking advantage of the fact that in certain circumstances you ignore the threading issues associated with dynamically updating whilst it's being dispatched by the drawing thread, however, this is a dangerous game to play that you have to be really careful to do without introducing a race condition. Whether you are just getting lucky in your code or it's genuinely safe I can't say as I don't have the code. In your case you are wanting a DataVariance of DYNAMIC_BUT_DRAW_TRAVERSAL_PLEASE_DONT_TREAT_ME_AS_SUCH. I guess the special case where modifying the data is safe would be STATIC_ALLOCATION_DYNAMIC_UPDATE or something along those line. Perhaps STREAM might be terminology that might fit this. However, even with the STREAM case if you are updating in the update or cull traversal while the draw thread is reading that same data you could get corrupted data sent to OpenGL driver, here you really should be double buffering. I'll ponder on this issue, but for now strictly speaking the VAO implementation is perfectly correct, requiring that the DataVariance be DYNAMIC is a correct interpretation of what the DataVariance is. Robert. _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
