[gl2ps] [patch] Enable use without an OpenGL context

[Christophe Geuzaine]

Hi David,

This is a very good idea - I've merged the patch in SVN.

Do you think it would be doable to incorporate the parsing of the transform feedback buffers directly in GL2PS?

Cheers,

Christophe

> On 12 Jan 2016, at 22:08, David Lonie <david.lonie at kitware.com> wrote:
> 
> Hi all,
> 
> I maintain the GL2PS export implementation in VTK, and we recently
> revamped our rendering engine to use newer OpenGL APIs, and the
> versions we're targeting have deprecated the OpenGL feedback buffer.
> 
> Not wanting to implement my own vector graphics export library, I've
> made a few modifications to GL2PS so that we may continue to use it,
> and would like to see about getting these merged upstream rather than
> make a fork of GL2PS. I've attached a diff made against the current
> (as of today) SVN repo.
> 
> For the curious, newer OpenGL adds Transform Feedback buffers that can
> be used to capture varying GLSL variables from vertex/geometry
> shaders. These buffers can provide transformed coordinates, normals,
> colors etc that the old feedback buffer used to catch. The buffers are
> parsed manually and the vertex attributes are added manually into
> gl2ps using gl2psAddPolyPrimitive.
> 
> Summary of changes:
> - Expose gl2psAddPolyPrimitive and required datatypes/defined values
> (the GL2PS_[...] primitive defines, GL2PSxyz, GL2PSrgba, and
> GL2PSvertex).
> - Allow gl2psBeginPage to accept a buffersize of 0 -- this indicates
> that the feedback buffer should not be parsed and that geometry will
> be supplied manually. This is a change in behavior -- the old
> implementation would allocate a default 4MB feedback buffer.
> - Add new gl2psForceRasterPos method, which allows the raster position
> to be set for text and image export without using OpenGL functions.
> 
> Feedback, questions, suggestions are welcome.
> 
> Cheers,
> Dave
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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