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FYI - There has been some talk about this here - <A HREF="http://www.paraview.org/pipermail/paraview/2005-September/002054.html">http://www.paraview.org/pipermail/paraview/2005-September/002054.html</A><BR>
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On Wed, 2014-01-08 at 12:43 -0500, Aashish Chaudhary wrote:
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Folks,
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While looking into some failing test on Linux, we realized this code below in vtkOpenGLRenderWindow
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// Initialize static member that controls global maximum number of multisamples
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// (off by default on Apple because it causes problems on some Mac models).
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#if defined(__APPLE__)
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static int vtkOpenGLRenderWindowGlobalMaximumNumberOfMultiSamples = 0;
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#else
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static int vtkOpenGLRenderWindowGlobalMaximumNumberOfMultiSamples = 8;
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#endif
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and in vtkXOpenGLRenderWindow.cxx
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if (multisamples)
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{
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#ifdef GLX_SAMPLE_BUFFERS_SGIS
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attributes[index++] = GLX_SAMPLE_BUFFERS_SGIS;
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attributes[index++] = 1;
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attributes[index++] = GLX_SAMPLES_SGIS;
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attributes[index++] = multisamples;
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#endif
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}
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Basically in OpenGL, we can achieve anti-aliasing for each primitive type by invoking enable / disable on <FONT COLOR="#000000">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 </FONT>GLX_SAMPLES_SGIS or ARB_multisample).
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<FONT COLOR="#000000">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). </FONT>
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<FONT COLOR="#000000">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?)</FONT>
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<FONT COLOR="#000000">Thoughts? </FONT>
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<FONT COLOR="#000000">Helpful links: </FONT>
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<A HREF="http://www.opengl.org/registry/specs/ARB/multisample.txt">http://www.opengl.org/registry/specs/ARB/multisample.txt</A>
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<A HREF="http://www.opengl.org/registry/specs/SGIS/multisample.txt">http://www.opengl.org/registry/specs/SGIS/multisample.txt</A><BR>
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<A HREF="http://www.opengl.org/wiki/Multisampling">http://www.opengl.org/wiki/Multisampling</A><BR>
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<FONT COLOR="#000000">- Aashish</FONT>
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-- <BR>
| Aashish Chaudhary <BR>
| R&D Engineer <BR>
| Kitware Inc. <BR>
| <A HREF="http://www.kitware.com">www.kitware.com</A>
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