OpenGL attrib_list support

[José Fonseca]

On Mon, Jul 8, 2013 at 2:30 PM, Alexander Monakov <amonakov at ispras.ru>wrote:

>
> On Mon, 8 Jul 2013, Alexander Monakov wrote:
>
> > Looks awesome.  Quick question -- is handling Xlib-style attrib-lists
> where
> > some keys stand alone without a corresponding value possible/easy?  This
> > should not block the patch, I'm just asking the question while the code
> is
> > hot (and I'm interested to have this functionality work for
> glXChooseVisual).
>
> Ah, sorry, I spoke too soon.  My concern is addressed by the pull request
> itself, to quote:
>
> > Note that the current code assumes no value for unknown keys when
> > determining attrib_list length, but int value when iterating over
> > attrib_list later. This has the effect that a null value after an unknown
> > key terminates the attrib_list as currently interpreted.
>
> You seem to explain a bug in your implementation? :)
>
> For GLX-style attrib-lists, you have a guarantee that a key is followed by
> a
> (possibly zero-bit-pattern) value.  Thus the attrib list is terminated by a
> zero-bit-pattern Int at an even position (thus, a key).  All values are at
> odd
> positions.
>
> For Xlib-style attrib-lists, you don't have that guarantee: keys for
> Boolean
> arguments do not have a value (it is implicitely 'True').
>
> Initially I thought your patch does not handle Xlib-style lists at all, but
> now it seems the ground work is in place?
>
> Alexander
>

I like the direction of the patch. I'd recommend adding a bool option to
AttribArray's constructor, so that when true, it would not assume a list of
pairs, but that bool attributes have implicit true value.

Jose
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