Re: [Freeglut-developer] OpenGL 3.0 support

[Steve B. <st...@sj...>]

Sven Panne wrote:
> As one can see, the required changes to freeglut are minimal: Give the user a 
> way to specify the major/minor version of the OpenGL context wanted, plus the 
> ability to specify a forward compatible/debug variant of it.
Sadly - that's nowhere near enough.   If the user were to use your new 
API to select
a GL context that's "3.1"-ish then a whole bunch of functionality 
disappears (and rightly
so, IMHO).  This includes (to pick a REALLY obvious example) 
"glBegin()...glEnd()".

That alone requires at least 70 source changes to freeglut.  (Mostly in 
freeglut_geometry.c
- but also in freeglut_menu.c, freeglut_font.c and freeglut_teapot.c).  
That's a very simple
example - but there is much worse to come.  The basic idea of "post 2.x" 
OpenGL is
that the fixed function pipeline is going to disappear.   That means 
that (for example)
we need to implement a shader to render the text in the glut font 
stuff...several shaders
in fact because we offer a choice between textured fonts and stroked fonts.

glutDrawTeapot uses all sorts of weird glMap2d and glEvalMesh2d stuff 
for bezier patch
skinning (I've been using OpenGL since the very first SGI implementation 
- and I've never
seen those calls used anywhere other than here!)  That functionality is 
probably going
away - so a total rewrite is called for.  Ideally - we should be using 
the new shader types
that allow you to skin patches using the GPU - but hardly any graphics 
cards support that
yet - so we may need to write our own patch skinning code in the CPU - 
in such a way
that we can migrate it over to the GPU once the majority of the world 
has that kind of
GPU hardware.   We could maybe steal the implementation of glMap2d and 
glEvalMesh2d
from Mesa's implementation...but still it's not gonna be simple.

That's only the stuff we'd be FORCED to change...we would also need to 
consider
revamping all of our demo programs to use 3.x technology.

  -- Steve