Description

Download

• Browse the source code
• Download vtkOffScreen.tar.gz

Usage

• On SGI systems compile with -DUSE_PBUFFER in the CFLAGS variable in the makefile in order to enable hardware accelerated rendering. On all other architectures (including older pre-Impact SGIs) use -DUSE_PIXMAP to compile it for software rendering. You can edit the Makefile to do this. (there ain't much to it)
• The Makefile will build two example programs; vtkSphere_ex and glxpixmap_ex. vtkSphere_ex will simply draw a vtkSphere offscreen and write it into a PPM image file called "sphere.ppm". glxpixmap_ex is a super-simple example of how the pixmap stuff is implemented in the VTK version.
• In your program you must turn ImmediateModeRendering on. This means either using vtkMapper::GlobalImmediateModeRenderingOn() or for each vtkMapper use mapper->SetImmediateModeRenderingOn().
• DO NOT use a vtkRenderWindowInteractor with this unless you want to cause it to crash with extreme prejudice. Other than that, you can use it just like you would another vtkRenderWindow.
• DO NOT use SetFullScreen() mode with this since there is no screen to test against. The pixmap will not respond correctly to X11 queries that were intended for mapped windows.
• This has never been used in stereo mode.

Caveats

• The offscreen renderer cannot handle vtkTexture directly due to some hardcoding in vtkOpenGLRenderWindow. So you will need to use the vtkOpenGLOffscreenTexture classes ( which are now included with this distribution) which were supplied by Randy Heiland of NCSA.
• So far I have been able to test on RedHat Linux 6.2 with Mesa and on SGI IRIX 6.4/6.5 systems (Impact,Octane and Onyx IR). I know that others have tested on SGI O2 and Sun workstations. That isn't a whole lot of systems, so I'm interested in any feedback about what systems it works/doesn't work on. The example program glxpixmap_ex.cc can be used as a simplified testbed to debug problems that might arise. The code in this example is the template for the vtk offscreen window.
• Rendering using the USE_PIXMAP version is really slow. There is really no way around this since it has to do with the vendor implementation of OpenGL rather than the methodology used. I wish hardware accelerated offscreen rendering was more widely available as part of standard OpenGL implementations.
• The system has been modified so that multiple PBUFFERS can be used simultaneously. However, it does incurr a performance cost by forcing the contents of the buffer to be copied out after every frame so as to preserve its contents and yield the buffer to other users on a system. You can get faster performance by putting the system into "exclusive" mode though. To do this, remove the #define USE_CLOSEDISPLAY from the top of the vtkOpenGLRenderWindow.cxx code. This will not yield the framebuffer between rendered frames thereby creating faster renders, but at the cost of making the framebuffer owned exclusively by a single renderer (no other user on the entire system will be granted access to this pipe until the offscreen renderwindow is destroyed).