[vtk-developers] Multisampling in VTK

[David E DeMarle]

We explicitly turn it off in specific tests where it has to be turned off
(depth compositing and surface selection for example).

My preference is that the default is 0 on all platforms, we make it simple
and obvious how to turn it on for apps that need higher quality images, and
we work to turn it off automatically whenever the features that require it
to be off are running.

David E DeMarle
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909


On Wed, Jan 8, 2014 at 12:43 PM, Aashish Chaudhary <
aashish.chaudhary at kitware.com> 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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