Re: [osg-users] Frame syncing over multiple contexts
Hi John, On 19 January 2012 20:58, John Kelso ke...@nist.gov wrote: OK then! This is getting good! I tried setting setEndBarrierPosition(BeforeSwapBuffers), setting setThreadingModel(CullDrawThreadPerContext), and running with four windows, each with a single camera, on a desktop system with a single graphics card, and the problem didn't go away. But should the problem go away in this environment? Without swap ready and gen lock you can't perfectly sync the displays. swap ready is a signal that all the rendering on a graphics card has completed and is ready to swap. gen lock is a hardware sync of the refresh itself that ensures that the scan for each display occurs at the same time. You can approximate a swap ready by doing a glFlush() or glFinish() prior to the swap barrier. The osg::BarrierOperation (implemented in include/osg/GraphicsThread) has support for doing either of glFlush or glFinish() prior to joining the barrier, but... currently osgViewer defaults to setting up the BarrierOperation with both of these off, just checking the source I see there isn't a access method for getting the end barrier. You could add this (subclassing from osgViewer::Viewer would give you a way of adding this), once you have the end barrier you'll be able to set the BarrierOperation::_preBlockOp. osgViewer::ViewerBase really should have this built in though so please feel free to add and submit it. Adding a glFlush() prior to the barrier will just make sure all the OpenGL fifo is dispatched to the graphics card, so isn't not everything will have completed on the graphics card before it returns. glFinish() prior to the barrier will make sure that the all the OpenGL fifo is dispatched and the graphics cards has completed all operations before it returns so you can be sure that things are properly ready to swap. There is one gotcha with all these though - waiting for the OpenGL pipeline to be flushed and completed down on the graphics card adds a delay on the CPU that breaks the parallelism between the CPU and GPU so performance can be lower. Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
On 01/20/2012 04:32 AM, Robert Osfield wrote: Hi John, On 19 January 2012 20:58, John Kelsoke...@nist.gov wrote: OK then! This is getting good! I tried setting setEndBarrierPosition(BeforeSwapBuffers), setting setThreadingModel(CullDrawThreadPerContext), and running with four windows, each with a single camera, on a desktop system with a single graphics card, and the problem didn't go away. But should the problem go away in this environment? Without swap ready and gen lock you can't perfectly sync the displays. swap ready is a signal that all the rendering on a graphics card has completed and is ready to swap. gen lock is a hardware sync of the refresh itself that ensures that the scan for each display occurs at the same time. This is four contexts on just one GPU and display, though. I don't think genlock/swap ready would come into play here. (glFlush/glFinish might, though) On a related note, does anyone know if the NV_swap_group extension mentioned earlier would work in the case of multiple contexts on one GPU/display, or does it only support synchronizing swap between GPUs/displays? --J ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
Hi all, We have seen the same behavior as Anna in our immersive system. It has four screens; each screen has a single graphics context and either one or two cameras (depends on if running in mono or stereo). The system is driven by an Nvidia quadroplex containing four FX5800 cards, one card per screen. We're running CentOS Linux. As a test I tried a configuration with one graphics context containing four cameras with non-overlapping viewports and in this case the graphics in all of the viewports appear to be updating at the same time. As a second test I tried a configuration with four graphics contexts on the same card, with each graphics context having a single camera. In this case I could see each window getting updated at a different time. I also tried setting the traits-swapGroupEnabled value to true but nothing changed. So as far as I can tell we are syncing swaps within a graphics context, but not between graphic contexts. At least that's how I interpret what I'm seeing. This may or may not be relevant, but we use one osgViewer::Viewer object and all of the cameras we use are slave cameras of the master camera in the viewer. Our graphics loop just calls osgViewer::Viewer::frame(). I see some methods in the osgViewer::ViewerBase class that might be relevant to the problem, but I'm unclear about which ones to set to what value. Any suggestions? Many thanks, John Hi Anna, Robbert, I think the bufferswaps on window are by default not synchronized, a call to wglJoinSwapGroupNV(HDC hdc, GLuint group) is needed to make different windows synchronize. the osg lib has the code to make the call, just set traits-swapGroupEnabled = true; before createGraphicsContext(traits); Output should look like: (set OSG_NOTIFY_LEVEL=INFO) GraphicsCostEstimator::calibrate(..) GraphicsWindowWin32::setSyncToVBlank on GraphicsWindowWin32::wglJoinSwapGroupNV (0) returned 1 GraphicsWindowWin32::wglBindSwapBarrierNV (0, 0) returned 0 the wglBindSwapBarrierNV fails if you don't have a gsync card (hardware connection card for multiple graphics cards) Still, as Robbert says, a single graphics window is likely to perform better, and is of course automatically in sync. But I suppose you don't want fullscreen with stereo mode VERTICAL_SPLIT. Laurens. On 1/16/2012 10:17 AM, Robert Osfield wrote: Hi Anna, This should work out of the box - the two windows should be rendering and synchronised. How are you setting up your viewer and graphics contexts? A a general note, if you are using a single graphics card for best performance one usually tries to use a single graphics window and have two cameras or more share this context. Is there a reason why you need two separate windows rather than a single window with two views? Robert. On 14 January 2012 21:21, Anna Sokolannaso...@gmail.com wrote: Hi, I am trying to figure out how to keep multiple graphics contexts in frame sync. My operating system is Windows XP SP3. My graphics is NVidia Quadro NVS 290 with the latest driver 276.42. I'm using OpenSceneGraph 3.0.1 compiled with Visual C++ 2005 for win32. I have vsync on in the driver and in Traits, also I am using a CullDrawThreadPerContext as the threading model. I have 2 graphics windows with separate contexts showing the same scene with a left and right view on one display. I have the scene moving across both windows so that I can see if its properly syncing. It sometimes visibly looks to be a number of frames out of sync (i.e. one of the rendered context is dragging behind). What could be causing this? In the threads? Or down in the graphics card? Is there any specific settings I should set to make the rendered contexts stay in frame sync? Regards, Anna Sokol ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
Hi John, On 19 January 2012 16:32, John Kelso ke...@nist.gov wrote: I also tried setting the traits-swapGroupEnabled value to true but nothing changed. swapGroupEnabled is only currently used under GraphicsWindowWin32 so won't effect linux systems in any way. So as far as I can tell we are syncing swaps within a graphics context, but not between graphic contexts. At least that's how I interpret what I'm seeing. This may or may not be relevant, but we use one osgViewer::Viewer object and all of the cameras we use are slave cameras of the master camera in the viewer. Our graphics loop just calls osgViewer::Viewer::frame(). As long as your run the viewer multithreaded the OSG will use a barrier so that each graphics thread waits at the end of draw dispatch, then once all the threads join this barrier then all move on together and then call swap buffers. This is done to try and achieve synchronized swapping, however, it's not a full proof scheme as it doesn't use any low level driver and hardware synchronization. Extensions to some OpenGL drivers exist to enable the low level synchronisation, such as swap groups, swap ready and gen lock. GraphicsWindowX11 doesn't have support for these extension. One could potentially add this into an existing application via a custom osg::Camera::FinalDrawCallback. It would be nice to have support for these extensions in the core though so feel free to pitch in ;-) Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
On 1/19/2012 9:57 AM, Robert Osfield wrote: As long as your run the viewer multithreaded the OSG will use a barrier so that each graphics thread waits at the end of draw dispatch, then once all the threads join this barrier then all move on together and then call swap buffers. Hi Robert -- The default value for ViewerBase::_endBarrierPosition appears to be AfterSwapBuffers. Does John need to change this to BeforeSwapBuffers in order to get the behavior you describe above? Thanks, -Paul ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
Hi Paul, On 19 January 2012 18:48, Paul Martz pma...@skew-matrix.com wrote: Hi Robert -- The default value for ViewerBase::_endBarrierPosition appears to be AfterSwapBuffers. Does John need to change this to BeforeSwapBuffers in order to get the behavior you describe above? Man I'm impressed, I'd forgotten implementing the EndBarrierPosition and the default. I presume I set the default to AfterSwapBuffers to avoid the possible performance drop in waiting for syncing the swap buffers dispatch. John should indeed change EndBarrierPosition to BeforeSwapBuffers using: viewer.setEndBarrierPosition(osgViewer::Viewer::BeforeSwapBuffers); ;-) Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
OK then! This is getting good! I tried setting setEndBarrierPosition(BeforeSwapBuffers), setting setThreadingModel(CullDrawThreadPerContext), and running with four windows, each with a single camera, on a desktop system with a single graphics card, and the problem didn't go away. But should the problem go away in this environment? We'll get a chance to test the same fix in our immersive environemnt soon and I'll report back. Many thanks, John On Thu, 19 Jan 2012, Robert Osfield wrote: Hi Paul, On 19 January 2012 18:48, Paul Martz pma...@skew-matrix.com wrote: Hi Robert -- The default value for ViewerBase::_endBarrierPosition appears to be AfterSwapBuffers. Does John need to change this to BeforeSwapBuffers in order to get the behavior you describe above? Man I'm impressed, I'd forgotten implementing the EndBarrierPosition and the default. I presume I set the default to AfterSwapBuffers to avoid the possible performance drop in waiting for syncing the swap buffers dispatch. John should indeed change EndBarrierPosition to BeforeSwapBuffers using: viewer.setEndBarrierPosition(osgViewer::Viewer::BeforeSwapBuffers); ;-) Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
Hi Anna, This should work out of the box - the two windows should be rendering and synchronised. How are you setting up your viewer and graphics contexts? A a general note, if you are using a single graphics card for best performance one usually tries to use a single graphics window and have two cameras or more share this context. Is there a reason why you need two separate windows rather than a single window with two views? Robert. On 14 January 2012 21:21, Anna Sokol annaso...@gmail.com wrote: Hi, I am trying to figure out how to keep multiple graphics contexts in frame sync. My operating system is Windows XP SP3. My graphics is NVidia Quadro NVS 290 with the latest driver 276.42. I'm using OpenSceneGraph 3.0.1 compiled with Visual C++ 2005 for win32. I have vsync on in the driver and in Traits, also I am using a CullDrawThreadPerContext as the threading model. I have 2 graphics windows with separate contexts showing the same scene with a left and right view on one display. I have the scene moving across both windows so that I can see if its properly syncing. It sometimes visibly looks to be a number of frames out of sync (i.e. one of the rendered context is dragging behind). What could be causing this? In the threads? Or down in the graphics card? Is there any specific settings I should set to make the rendered contexts stay in frame sync? Regards, Anna Sokol _ Once we accept our limits, we go beyond them. -- Albert Einstein ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Frame syncing over multiple contexts
Hi Anna, Robbert, I think the bufferswaps on window are by default not synchronized, a call to wglJoinSwapGroupNV(HDC hdc, GLuint group) is needed to make different windows synchronize. the osg lib has the code to make the call, just set traits-swapGroupEnabled = true; before createGraphicsContext(traits); Output should look like: (set OSG_NOTIFY_LEVEL=INFO) GraphicsCostEstimator::calibrate(..) GraphicsWindowWin32::setSyncToVBlank on GraphicsWindowWin32::wglJoinSwapGroupNV (0) returned 1 GraphicsWindowWin32::wglBindSwapBarrierNV (0, 0) returned 0 the wglBindSwapBarrierNV fails if you don't have a gsync card (hardware connection card for multiple graphics cards) Still, as Robbert says, a single graphics window is likely to perform better, and is of course automatically in sync. But I suppose you don't want fullscreen with stereo mode VERTICAL_SPLIT. Laurens. On 1/16/2012 10:17 AM, Robert Osfield wrote: Hi Anna, This should work out of the box - the two windows should be rendering and synchronised. How are you setting up your viewer and graphics contexts? A a general note, if you are using a single graphics card for best performance one usually tries to use a single graphics window and have two cameras or more share this context. Is there a reason why you need two separate windows rather than a single window with two views? Robert. On 14 January 2012 21:21, Anna Sokolannaso...@gmail.com wrote: Hi, I am trying to figure out how to keep multiple graphics contexts in frame sync. My operating system is Windows XP SP3. My graphics is NVidia Quadro NVS 290 with the latest driver 276.42. I'm using OpenSceneGraph 3.0.1 compiled with Visual C++ 2005 for win32. I have vsync on in the driver and in Traits, also I am using a CullDrawThreadPerContext as the threading model. I have 2 graphics windows with separate contexts showing the same scene with a left and right view on one display. I have the scene moving across both windows so that I can see if its properly syncing. It sometimes visibly looks to be a number of frames out of sync (i.e. one of the rendered context is dragging behind). What could be causing this? In the threads? Or down in the graphics card? Is there any specific settings I should set to make the rendered contexts stay in frame sync? Regards, Anna Sokol _ Once we accept our limits, we go beyond them. -- Albert Einstein ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
