[vtk-developers] vtkGL2PSExporter: need feedback.

[Jeff Lee]

Hi Prabhu,
In my experience, converting directly to postscript produces notoriously 
bad images, and is generally not a huge benefit (except for very simple 
scenes).  One reason is that the algorithms used to produce shaded 
polygons actually recursively subdivide the gl polygon to produce many 
flat-shaded postscript polygons, resulting in a huge file size.  The 
whole concept of gl2ps is to turn the postscript rendering engine into a 
gl rendering engine, and to do that there are many sacrifices.  For 
example, transparency doesn't work (well if at all).  The overall idea 
is nice, but in practice doesn't work well in all situations.  That 
being said, I don't think it is a good addition to vtk.  I am not on the 
ARB, but I would not like to see vtk polluted with external libraries 
without a really good reason.  I think that vtkWindowToImageFilter 
serves this need the best right now.  But I do appreciate your constant 
improvements to vtk and I am willing to hear any other arguments.  What 
do others feel?
Regards,
-Jeff

Prabhu Ramachandran wrote:

>hi,
>
>I now have a working vtkGL2PSExporter class that works fine for me
>with a few useful options (DrawBackgroundOn/Off, DrawTextOn/Off,
>LandscapeOn/Off and support for PS, EPS, and TeX).  I've managed to
>setup my vtkLocal build to work nicely with gl2ps.  Thanks to whoever
>wrote the vtkMy examples -- Sebastien?
>
>Anyway, I think it should be easy for me to incorporate the class into
>VTK.  I'll have to modify CMakeLists.txt in a few places.  So if no
>one has serious objections to this I'll commit the code sometime and
>see how it goes.
>
>As I had mentioned earlier, none of the text appears.  I think one way
>of handling text would be to modify the vtkTextMapper
>(vtkOpenGLFreeTypeTextMapper?) so that when it is Rendering, if
>VTK_USE_GL2PS is defined we simply call gl2psText(...) with the
>appropriate text, font etc.  In order that this is done at the right
>time we could add a static member to the class that is turned on only
>when the gl2ps exporter is writing its data.  I'd appreciate if a more
>experienced person with the text mappers (Sebastien again?) would care
>to comment on this or discuss this with me sometime.
>
>Thanks.
>prabhu
>
>p.s. I've also completed the translation of the Tcl example scripts to
>Python.  There are 82 Python examples.  About 13 of the Tcl examples
>are not translated because they create non-trivial Tk based GUIs.
>I've left these alone.
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>  
>

-- 
Jeff Lee <jeff at cdnorthamerica.com>
Software Engineer
CD North America
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