[osg-users] ImageStream and texture updates synch
Hi, From what I understand, an ImageStream indicates that the image as been changed by calling the dirty() method. From there, a texture will update its content with the new image when the scenegraph is traversed. The problem is that I've not found any way to synchronize the point where the ImageStream updates its current image and where a texture update its content with the current image, which leads to visual tearing (very similar to vsync off) if the ImageStream and the texture update their content at the same time. This is quite visible on some videos when using the FFmpeg plugin. Any ideas? Cheers, Tanguy ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] ImageStream and texture updates synch
HI Tanguy, You don't want a synchronization point in the image stream as it'd cause the rendering thread to stall waiting for the movie reading thread. Rather than add such a sync operation, it's best to double buffer the image data and then just do a pointer swap on the image to tell it which buffer is current, this is what I implemented in the xine-lib plugin. Something else I have been wondering about is the possibility of having two ImageStream that are managed so that they are one frame apart, then in the graphics thread you'd have a geometry with two textures applied, and a mixing of the two textures based on the time for the rendering frame vs the time of each of the texture. This way one might be able to provide a smoother video experience. I must admit, I don't know how effective this would be on movies, but it might be an interesting thing to try out further down the line. Robert. On Mon, Mar 2, 2009 at 4:44 PM, Tanguy Fautre tang...@aristechnologies.com wrote: Hi, From what I understand, an ImageStream indicates that the image as been changed by calling the dirty() method. From there, a texture will update its content with the new image when the scenegraph is traversed. The problem is that I’ve not found any way to synchronize the point where the ImageStream updates its current image and where a texture update its content with the current image, which leads to visual tearing (very similar to vsync off) if the ImageStream and the texture update their content at the same time. This is quite visible on some videos when using the FFmpeg plugin. Any ideas? Cheers, Tanguy ___ 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] ImageStream and texture updates synch
Hi Robert, It's then probably a good idea to update the ffmpeg plugin to also use a pointer swap. The current implementation of the ffmpeg plugin is not optimal. Internally there are already two buffers (a private and a public one), because of the colour conversion routines, synch issues, and also because of the vertical orientation (see void FFmpegDecoderVideo::swapBuffers()). FFmpegDecoderVideo::publishFrame() and FFmpegDecoderVideo::swapBuffers() could be improved to feature a real double buffering (and remove the then-useless copy) so that FFmpegImageStream could implement a pointer swap. I think I could tackle this and submit the modifications during this week. Tanguy -Original Message- From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Robert Osfield Sent: Monday 02 March 2009 17:07 To: OpenSceneGraph Users Subject: Spam: Re: [osg-users] ImageStream and texture updates synch HI Tanguy, You don't want a synchronization point in the image stream as it'd cause the rendering thread to stall waiting for the movie reading thread. Rather than add such a sync operation, it's best to double buffer the image data and then just do a pointer swap on the image to tell it which buffer is current, this is what I implemented in the xine-lib plugin. Something else I have been wondering about is the possibility of having two ImageStream that are managed so that they are one frame apart, then in the graphics thread you'd have a geometry with two textures applied, and a mixing of the two textures based on the time for the rendering frame vs the time of each of the texture. This way one might be able to provide a smoother video experience. I must admit, I don't know how effective this would be on movies, but it might be an interesting thing to try out further down the line. Robert. ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
