Re: POV-Ray Terminal

[Timothée L. <tim...@lp...>]

Daniel Farrell a écrit :
> Hello,
>
> I was listing to the latest FLOSS Weekly Podcast (http://twit.tv/ 
> floss24) in which the topic was POV-Ray; an open source ray tracing  
> program. After some idle surfing I found that somebody has contributed  
> patches to gnuplot for a POV-Ray terminal; fancy ray-traced figures  
> found here, (http://t-kita.net/gnuplot_povrml/) and the submitted  
> patch here, (http://sourceforge.net/tracker/index.php?func=detail&aid=1262281&group_id=2055&atid=302055 
> ).
>
> I cannot apply this patch successfully to the gnuplot-4.0.0 source? I  
> am going like this,
>
> cp -r gnuplot-4.0.0 gnuplot
> cp -r gnuplot gnuplot-patch
> mv povray.diff gnuplot
> cd gnuplot
> patch -p1 < povray.diff
>
> Anybody have gnuplot and POV-Ray working together?
>
> Cheers,
>
> Dan.
>
>
>   
Hi Daniel,

You have found a wonderful peace of work there ! The povray figures that 
are given in http://t-kita.net/gnuplot_povrml/ are simply gorgeous. The 
two authors, KITA Toshihiro and MIYATA Shigeo, have done something that 
others (I included) have probably dreamed of sometimes : let the 
terminal driver handle 3D instead of letting gnuplot core do all the 
work. Here POV-ray gives a very valuable addition compared to gnuplot 3D 
routines : it does true (isometric) perspective, plus realistic shading, 
something that is desperately lacking in gnuplot today. There is a patch 
on SF.net for adding perspective to gnuplot 3D routines, but the author 
did not work on it until inclusion in CVS, and as far as shading (or, 
plot points as little spheres, etc), I had never seen such a thing for 
gnuplot.

There's at least one thing that this work has not achieved according to 
the figures : it's pm3d coloring, which is very important for 3d data 
visualization. Perspective + shading + pm3d coloring of surfaces plots 
would be a great achievement. Let me add that POV-ray, like openGL, is 
probably able to draw polygons colored with gradients, something that is 
very difficult or impossible with most 2D drawing API (Cairo, for 
example, cannot do it). Gradients coloring makes surface plots much 
nicer, and gnuplot already has the mechanisms to do that, but they are 
used by a single terminal driver, namely the SVGA one, the one that 
Ethan never achieved to see working, the one that is also presumably 
unsecure. Too bad, isn't it ?

Let's talk about the code now.
You mention the following patch : 
http://sourceforge.net/tracker/index.php?func=detail&aid=1262281&group_id=2055&atid=302055 
. This is not the patch that gave the POV-ray figures. This patch on 
SF.net only does 2D rendering, as the author, Gaël Varoquaux, explains 
on the page:
> This patch is not terribly iseful as long as the 2D/3D code
> in gnuplot is not refactored. This patch only implements the
> 2D drawing API (as there is no 3D API currently).

However, the right patch is provided in 
http://t-kita.net/gnuplot_povrml/gnuplot_povrml-0.3.patch
First, it is offered as a public domain work, so there is no license 
issue. Good.
It's not really large:
> # diffstat gnuplot_povrml-0.3.patch
>  src/plot2d.c    |   21 ++
>  src/plot3d.c    |   19 +
>  src/povray.c    |  538 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/term.h      |    6
>  src/vrml.c      |  399 +++++++++++++++++++++++++++++++++++++++++
>  term/povray.trm |  152 +++++++++++++++
>  term/vrml.trm   |  151 +++++++++++++++
>  7 files changed, 1286 insertions(+)
However, after a quick glance at the patch, it's not in a state that 
would allow it to be included immediately. The authors have bypassed 
gnuplot terminal system almost completely, and only 'splot' seems to be 
possible.

Steps to make that patch better :
- make it work with gnuplot CVS,
- identify key functions to design an API to extend the current terminal 
one in gnuplot.
- get full 2D + 3D (maybe mix this patch with Gaël's one)

Thanks Daniel for making this work known !
Best regards,

Timothée Lecomte