EGL_MESA_screen_surface version 5

[Jim Gettys]

FWIW: we need to move to a model where everything is dynamic, including
screens, given modern hotplug hardware and software systems.

So try to keep that in mind, while doing the API design...
				- Jim

On Fri, 2005-04-22 at 12:19 -0400, Adam Jackson wrote:
> On Wednesday 06 April 2005 18:12, Brian Paul wrote:
> 
> I've been implementing this in my IndieGL toy and I've found a few issues.
> 
> eglScreenPositionMESA() is listed in the Additions section but not in the New 
> Procedures and Functions section.
> 
> >    EGLBoolean eglQueryDisplayMESA(EGLDisplay dpy, EGLint screen_number,
> >                                   EGLint attrib, EGLint *value)
> >
> >    Used to query display parameters.  <attrib> may be one of the following:
> >
> >        Name                Return value description
> >        ------------------  ---------------------------------------------
> >        EGL_NUM_SCREENS     Number of screens associated with the display
> 
> In the new tokens section this was called EGL_SCREEN_COUNT_MESA.
> 
> I don't see any semantic value in passing a screen_number to QueryDisplay, are 
> we just leaving that in for future expansion?
> 
> There's a minor issue here, in that it's not clear whether 
> EGL_SCREEN_COUNT_MESA is the number of active screens or the number of 
> possible screens.  This is more of an issue for me trying to do a GLX wrapper 
> than it probably is for real hardware, for now anyway, but who knows how 
> hotpluggable things will be in the future.  
> 
> I suggest the following clarification.  EGL_SCREEN_COUNT_MESA is the maximum 
> number of screens on the device, where zero indicates that the device is 
> hotpluggable.  EGLint screen_number parameters are valid in the range 0 to 
> EGL_SCREEN_COUNT_MESA-1 when ESCM is >0.  When ESCM == 0, you may check the 
> validity of a particular screen_number by calling QueryScreenSurface on it.  
> EGL_FALSE/EGL_BAD_SCREEN_MESA indicates an invalid screen number; EGL_TRUE 
> indicates a valid screen number with possibly no screen surface currently 
> being displayed.
> 
> When doing EGL-GLX translation you can create arbitrary numbers of screens, 
> because they're just windows, so CreateScreenSurface can just fail or succeed 
> based on whether XCreateWindow works.  That should work for more distributed 
> setups too, but there might need to be a new entrypoint to hand the 
> application an opaque screen_number to use.  Not something I think we need to 
> design now though.
> 
> - ajax
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