[Fluxus] rfc: (draw-line)

[David Griffiths]

Hi all,

On Sat, 2010-10-09 at 22:29 +0200, gabor papp wrote: 
> > I haven't even seen the fluxus code, but I can't help but to wonder
> > why should this be more complicated than
> >
> > glBegin(GL_LINES)
> > glVertexfv(startVector);
> > glVertexfv(endVector);
> > glEnd();
> >
> of course, at the end the line rendering is something like this. but 
> fluxus has a more complex system. when you run (draw-cube) the cube is 
> not drawn in that exact moment. fluxus has a scene graph for storing 
> objects and their render states. you add objects to the scene graph with 
> (build-*) commands, and when you use (colour) for instance, you modify 
> the actual render state. (draw-*) commands are special. all (draw-*) 
> primitives are registered, and they are displayed after the scene graph 
> is rendered in every frame. so if you ran something like the code above 
> when (draw-line) is executed it would not produce anything visible, 
> because it would be overwritten by the rendering of the scene graph.

Also the line primitive is a little more than GL_LINES as in one form it
builds camera facing geometry.

>From my POV I think for immediate mode it would be better to have just a
GL_LINES approach, as creating and deleting primitives is quite costly.

cheers,

dave