[vtk-developers] Multisampling in VTK

[Sankhesh Jhaveri]

FYI -  There has been some talk about this here -
http://www.paraview.org/pipermail/paraview/2005-September/002054.html

-- 


On Wed, 2014-01-08 at 12:43 -0500, Aashish Chaudhary wrote:
> Folks, 
> 
> 
> 
> While looking into some failing test on Linux, we realized this code
> below in vtkOpenGLRenderWindow 
> 
> 
> // Initialize static member that controls global maximum number of
> multisamples
> // (off by default on Apple because it causes problems on some Mac
> models).
> #if defined(__APPLE__)
> static int vtkOpenGLRenderWindowGlobalMaximumNumberOfMultiSamples = 0;
> #else
> static int vtkOpenGLRenderWindowGlobalMaximumNumberOfMultiSamples = 8;
> #endif
> 
> 
> 
> 
> and in vtkXOpenGLRenderWindow.cxx
> if (multisamples)
>     {
> #ifdef GLX_SAMPLE_BUFFERS_SGIS
>     attributes[index++] = GLX_SAMPLE_BUFFERS_SGIS;
>     attributes[index++] = 1;
>     attributes[index++] = GLX_SAMPLES_SGIS;
>     attributes[index++] = multisamples;
> #endif
>     }
> 
> 
> Basically in OpenGL, we can achieve anti-aliasing for each primitive
> type by invoking enable / disable on GL_POINT_SMOOTH, GL_LINE_SMOOTH
> or GL_POLYGON_SMOOTH. The other route that applies anti-aliasing to
> all of the primitives is to use mutli-sampling if available (this
> always wins if both methods are used). Now by default, on LINUX (the
> code above set the sample size to 0 effectively disabling
> anti-aliasing) we have anti-aliasing ON with a sample size of 8. The
> anti-aliasing is an expensive operation and not all of the
> implementation supports it (Please refer to the documentation
> on GLX_SAMPLES_SGIS or ARB_multisample). 
> 
> 
> I am asking if we should set the sample size to 0 default on Linux as
> well (like Mac) and if applications needs it then they can explicitly
> turn it ON. I can make an argument for either side but I am bit more
> inclined towards setting it to 0 so that applications can still
> control it if wanted but if not they won't get it by default (and will
> get better performance overall). 
> 
> 
> Now we don't agree on this, can we agree on setting to 0 for testing
> (May be via environment variable like others we used in our testing?)
> 
> 
> 
> 
> Thoughts? 
> 
> 
> Helpful links: 
> http://www.opengl.org/registry/specs/ARB/multisample.txt
> http://www.opengl.org/registry/specs/SGIS/multisample.txt
> 
> http://www.opengl.org/wiki/Multisampling
> 
> 
> 
> 
> 
> - Aashish
> 
> 
> 
> 
> 
> 
> 
> -- 
> | Aashish Chaudhary 
> | R&D Engineer         
> | Kitware Inc.            
> | www.kitware.com    
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