[vtkusers] What Is Off-Screen ?

[Sylvain Jaume]

Hi Mark,

Read this thread from Francois Bertel to know if offscreen is supported 
by your card:
http://public.kitware.com/pipermail/vtkusers/2007-September/092480.html

Note that 'glxinfo' was missing in the message. The message must read:
"
To check the available extensions on your system:

* Under Linux, check the list of extensions with command line *glxinfo*
* Under MacOSX, with Xcode installed, Macintosh 
HD->Developer->Applications->Graphic Tools->OpenGL Driver 
Monitor.app->Monitors->Renderer Info-><name of the OpenGL 
driver>->OpenGL Extensions
* Under Windows, you can download and use GLview 
http://www.realtech-vr.com/glview
"

Offscreen rendering has nothing to do with any mapper. But internally, 
the volume mapper uses some intermediate framebuffer object.

About the volume mapper itself (from yesterday), the following 
extensions are required:

* OpenGL>=1.3 (for clamd_edge extension and multitexture)
* OpenGL>=2.0 or GL_ARB_draw_buffers
* extension GL_ARB_fragment_program
* extension GL_ARB_vertex_program
* extension GL_EXT_framebuffer_object
* extension GL_ATI_texture_float or GL_ARB_texture_float

Optional extension:
* OpenGL>=1.5 or GL_ARB_vertex_buffer_object

Sincerely,
Sylvain
PS: Please keep your messages on vtkusers mailing list.

JohnMark wrote:
> thank you for your help , Sylvain ,
>  
>     and I test the vtkOpenGLHAVSVolumeMapper just now , but there is a 
> error : Required OpenGL
> extensions not supported! what's more , the volume rendering is all 
> white and there is not any other
> color in it ,so I want to ask : if I want to use Off-Screen , my 
> computer should have to support the
> OpenGL extensions ? or I would get many errors and  get a 
> unicolor volume rendering ? and is the
> color couldn't be mapped by the Off-Screen ? or there is a loss in color 
> of the rendering ?
>  
>     these are my current doubt , and thank you for your articles , 
> I think I should read it right now !
>  
>
>     thank you with great regards again !
>    
>     Mark 
>      
>  
> ------------------------------------------------------------------------
> 
>  > Date: Mon, 17 Sep 2007 11:49:33 -0400
>  > From: sylvain.jaume at kitware.com
>  > To: zhaojunxp at hotmail.com
>  > CC: vtkusers at vtk.org
>  > Subject: Re: [vtkusers] What Is Off-Screen ?
>  >
>  > Mark,
>  >
>  > I'd like to add this:
>  >
>  > Currently you can do offscreen rendering on Linux with hardware
>  > acceleration but a window will pop up. To avoid this, you need to link
>  > VTK with Mesa *and* turn on the OSMESA option when configuring VTK with
>  > CMake.
>  >
>  > In the vtkOpenGLHAVSVolumeMapper, offscreen rendering means that the
>  > rendering happens in a framebuffer object smaller than or equal to the
>  > screen size. As a final step, the colorbuffer of this framebuffer object
>  > is mapped to the full size of the screen. This allows image-based
>  > level-of-detail to meet interactive rendering.
>  >
>  > For references about the HAVS algorithm and the level-of-detail
>  > algorithm, I'd point you to these papers:
>  >
>  > "Hardware-Assisted Visibility Sorting for Unstructured Volume Rendering"
>  > by S. P. Callahan, M. Ikits, J. L. D. Comba, and C. T. Silva, IEEE
>  > Transactions of Visualization and Computer Graphics; May/June 2005.
>  >
>  > "Interactive Rendering of Large Unstructured Grids Using Dynamic
>  > Level-of-Detail" by S. P. Callahan, J. L. D. Comba, P. Shirley, and C.
>  > T. Silva, Proceedings of IEEE Visualization '05, Oct. 2005.
>  >
>  > Sincerely,
>  > Sylvain
>  >
>  > Sylvain Jaume wrote:
>  > > Hi Mark,
>  > >
>  > > Setting OffScreenRenderingOn() on your vtkRenderWindow will not 
> display
>  > > the rendering. Note that on Linux you need to link VTK with Mesa.
>  > >
>  > > Sincerely,
>  > > Sylvain
>  > >
>  > > JohnMark wrote:
>  > >> Hi , everyone ,
>  > >> I always see that this is off-screen technique and so on when I
>  > >> read some information of VTK
>  > >> classes , for example vtkHAVSVolumeMapper . but I really don't know
>  > >> what is off-screen technique and why
>  > >> we have to use it . and now I have searched a lot of information ,
>  > >> however , they all say that they use
>  > >> it , but I cann't get what it is in detail .
>  > >> so can you help me to give me some hints , information , or
>  > >> articles ?
>  > >>
>  > >> thank you with great regards !
>  > >>
>  > >> Mark
>  > >>
>  > >> 
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