[AD] Behavior of OpenGL on Mac OS X

[Evert Glebbeek <eglebbk@xxxxxxxxxx>]

After following some of the discussion here and looking at the OpenGL  
implementation on OS X, I realised that it seems to be a bit different  
from the other platorms.
Leaving aside for the moment that  
osx_get_opengl_pixelformat_attributes() doesn't return the attributes  
for the actual mode that was set (I know how to do that, but haven't  
got round to it yet), there seem to be the following differences:

1. When picking a colour format, Cocoa doesn't allow you o specify the  
size of the individual colour components: just the overall colour  
depth and the depth of the alpha channel. What should the display's  
"format" field be set to after the mode set? At the moment, it's set  
to ALLEGRO_PIXEL_FORMAT_RGBA_8888, which is probably wrong.
There is no obvious way to set the size of individual colour  
components using Cocoa, so those settings are ignored. I'm not sure if  
this is ideal.
2. Using the Carbon/AGL (Apple Graphics Library) interface to OpenGL,  
it *is* possible to set a particular combination of RGB sizes.  
However, there is no obvious way that I can find to create an OpenGL  
context using AGL and use that instead of an NSOpenGLContext object.
3. No "display scoring" is used by Allegro itself - the NSOpenGL class  
does this on its own. In a way, I like this, but it does introduce a  
potential difference in how Allegro behaves on OS X compared to other  
platforms.

So I guess my main questions are:
1. How should I set the "format" field in the display struct? Anything  
that matches the requested colour depth+alpha size?
2. Do we care sufficiently strongly about being able to set the red/ 
green/blue bit sizes that we should consider using AGL instead of  
NSOpenGL? If the answer is yes, I'm not the one who is going to do  
it. ;) Personally I don't think this is all that important.  
Aternatively, maybe someone can suggest a way to combine an AGL- 
created context with an NSOpenGLView?
3. Is it a potential problem that OS X OpenGL uses its own display  
scoring independent of Allegro? Again, personally I don't think so.

Evert