Re: Help needed to update our use of OpenGL

[John W. Eaton]

On 09/12/2018 03:54 PM, Pantxo wrote:

> Yes, among what we use, the so called fixed pipeline is deprecated and won't
> be necessarily part of future implementations. At best, those functions will
> get no attention and stay there but become more and more buggy without a
> hope for a fix.
> The GL_FEEDBACK mode, on which we rely for printing, is also deprecated and
> I have no hope that e.g. the bug below will get fixed:
> https://savannah.gnu.org/bugs/?func=detailitem&item_id=48689


That's also my thinking.  Even though these interfaces are not likely to 
go away any time soon, it probably doesn't help us to continue using them.

> VTK is already using modern OpenGL so it may be worth looking at their code.
> For printing, they directly feed gl2ps with primitives they fetched in a
> transform feedback buffer(see [1] and [2]).

Thanks for the pointers.  Having examples is helpful.

> I never programmed anything in modern OpenGL, so I can't really help, but if
> such restructuring should happen I'd be happy to discuss the opportunity of
> abstracting our current opengl_renderer into something more general, say
> base_render. The latter would be "rendering technology agnostic" (actual
> drawing and property changes are done in pure virtual functions) and would
> serve as a base for the opengl_renderer and eventually for any kind of 2D-3D
> renderer someone may want to implement (I was thinking about qt_renderer,
> cairo_renderer for 2D printing).
Yes, I think this kind of refactoring would be good.  We could also move 
in this direction independently of updating our use of OpenGL.

jwe