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Re: Do we really need to replace gnuplot?

From: kahacjde
Subject: Re: Do we really need to replace gnuplot?
Date: Wed, 17 Oct 2007 03:32:34 -0700 (PDT)

Shai Ayal-2 wrote:
> On 10/15/07, Alexander Barth <address@hidden> wrote:
>> On 10/15/07, Shai Ayal <address@hidden> wrote:
>> > On 10/15/07, John W. Eaton <address@hidden> wrote:
>> > > On 15-Oct-2007, Shai Ayal wrote:
>> > >
>> > > | But are you willing to sacrifce offscreen rendering for them?
>> > >
>> > > Precisely what do you mean by offscreen rendering?
>> >
>> > I mean the ability to produce a plot in a file (e.g ps or png) w/o the
>> > need for opening a window or indeed using any graphical capabilities
>> > in the computer. gnuplot does this easily, However OpenGL is meant for
>> > screen rendering, so even if you wish to produce a png file, you must
>> > first render the scene to the screen and then convert it to a png
>> > file.
>> >
>> > There might be a solution for this using OpenGL pbuffers. I'm looking
>> into
>> it ..
>> >
>> > Shai
>> You can do off-screen rendering in opengl with GLX Pixmap and OS Mesa.
>> For GLX Pixmap you need a connection to a X server but no window is
>> displayed. This is not necessary for OS Mesa. A nice overview can be
>> found
>> here:
>> http://www.mesa3d.org/brianp/sig97/offscrn.htm
>> Also, toolkits such as GTK (gtkglext) provide a higher level interface
>> for
>> off-screen pixmaps.
>> http://gtkglext.sourceforge.net/reference/gtkglext/gtkglext-gdkglpixmap.html
>> The advantage of using a toolkit for off-screen rendering is that your
>> code
>> is probably more portable.
> It looks to me like gtkglext does require a connection to an x-server,
> which I don't think we should require of windows and mac users.
> osmesa seems like the way to go, but I must ascertain that it exists
> for windows and mac before I commit
> thanks for the tips
> Shai
>> Alex

In addtion it could be interesting to have look at the method used in
OpenInventor/Coin3D. They provide a SoOffscreenRenderer Class that allows
for off-screen rendering with RGB and Postscript support.

To cite the relevant part:
"Offscreen rendering is internally done through either a GLX offscreen
context (i.e. OpenGL on X11) or a WGL (i.e. OpenGL on Win32) or AGL (i.e.
OpenGL on the Mac OS) ditto. If the OpenGL driver supports the pbuffer
extension, it is detected and used to provide hardware-accelerated offscreen


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