getframe() alternatives

[PhilipNienhuis]

While porting a ML script that creates a video clip to Octave I stumbled upon
the lack of getframe().
The OF video package (or should it be: the image package) still lacks that.

The reason I ask on Maintainers is that I seek for coding advice.

For now I have the following clumsy solution for adding successive screen
images (plots) to an avi stream:

Alternative 1
==========
<for ...>
  <...create plot with filled contours, pimp it...>
  print ("tmp.fig", "-dppm");
  HH = im2double (imread ("tmp.fig"));
  aviobj = addframe (aviobj, HH);
<endfor>

...which works. But of course, very slowly. 
(FYI: im2double() (OF image pkg) converts to double and scales to [0..1]
just as addframe() (OF video pkg) requires.)


Alternative 2
==========
I figured (but I may be wrong) that skipping the disk write/read portions
may save considerable amounts of time. So would it be possible to have
print() write to a pipe rather than file, and imread() read from a pipe
rather than file? That might be the most platform-independent "kludge".


Alternative 3
==========
Obviously a genuine binary getframe() solution is preferable. Apart from
skipping disk I/O it would avoid double graphics format conversion as well
and simply transfer the screen image representation in video memory into a
bitmap in the form of a 3D array.

On Windows (where I work on for this ML script) this should be a breeze once
the screen API graphics handle is available. FLTK would be the way to go
then; Gnuplot is a separate prog so access to its internals is probably a
bit hard. 
Over a decade ago I once made something like that for a screen grab routine
in assembly language; however yesterday a google search turned up dozens of
much better designed examples in C / C++ / C# etc.
However I have no idea where to search for the graphics handle in the
Octave/FLTK sources. Or is it hidden in the FLTK libs and never used
directly by Octave?

On Linux I wouldn't know how to proceed, but I presume graphics handles are
also used there.

Is there any advice on how to most efficiently get a bitmap/3D array out of
an Octave graphics handle? perhaps even code snippets?

Thanks,

Philip


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