[Mesa-dev] [RFC] New EGL extension: EGL_EXT_platform_display

[Eric Anholt]

Chad Versace <chad.versace at linux.intel.com> writes:

> On 02/20/2013 05:44 PM, Eric Anholt wrote:
>> Chad Versace <chad.versace at linux.intel.com> writes:
>> 
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>>> I'm seeking feedback on an EGL extension that I'm drafting. The ideas have
>>> already been discussed at Khronos meetings to a good reception, but I want
>>> feedback from Mesa developers too.
>>>
>>> Summary
>>> - -------
>>> The extension, tentatively named EGL_EXT_platform_display, enables EGL clients
>>> to specify to which platform (X11, Wayland, gbm, etc) an EGL resource
>>> (EGLDisplay, EGLSurface, etc) belongs when the resource is derived from
>>> a platform-native type. As a corollary, the extension enables the creation of
>>> EGL resources from different platforms within a single process.
>>>
>>>
>>> Feedback
>>> - --------
>>> I'd like to hear feeback about the details below. Do you see any potential
>>> problems? Is it lacking a feature that you believe should be present?
>> 
>> Seems pretty reasonable as an outline.  I'm not clear, though, what are
>> the rules on sharing EGL resources like EGLImages between EGLDisplays?
>
> If I interpreted correctly all the pertinent EGL specs, currently no resource
> sharing is allowed between EGLDisplays. So, the EGL_EXT_display_platform
> doesn't need to define additional restrictions here.
>
> Here's my reasoning based on my interpretation of the specs. I can think of
> four resources that can potentially be shared:
>
>   - EGLContext
>
>     The EGL 1.4 spec states that all contexts in a share group must belong to
>     the same display. This restriction should not be lifted by
>     EGL_EXT_platform_display.
>
>   - EGLSurface
>
>     I could find no text in the EGL 1.4 discussing sharing of EGLSurfaces, so the
>     EGL_EXT_platform_display spec should explicitly ban sharing them between
>     displays from different platforms. If necessary, a layered extension can add
>     sharing for special cases.
>
>   - EGLImage
>
>     EGLImages are created with respect to an EGLDisplay and EGLContext, so I
>     assume that they can be shared only among contexts within same share group.
>     The EGL_KHR_image_base specs give any useful details about sharing.
>
>   - EGLStream
>
>     An EGLStream is created with respect to an EGLDisplay, but not a context.
>     Because the spec does not say otherwise, I assume EGLStreams also cannot
>     be shared across displays.

Good to hear.
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