[Mesa-dev] [PATCH 1/3] egl/android: Delete set_damage_region from egl dri vtbl

[Eric Anholt]

Harish Krupo <harish.krupo.kps at intel.com> writes:

> Hi Eric,
>
> Eric Anholt <eric at anholt.net> writes:
>
>> Harish Krupo <harish.krupo.kps at intel.com> writes:
>>
>>> The intension of the KHR_partial_update was not to send the damage back
>>> to the platform but to send the damage to the driver to ensure that the
>>> following rendering could be restricted to those regions.
>>> This patch removes the set_damage_region from the egl_dri vtbl and all
>>> the platfrom_*.c files.
>>> Then upcomming patches add a new dri2 interface for the drivers to
>>> implement
>>>
>>> Signed-off-by: Harish Krupo <harish.krupo.kps at intel.com>
>>
>> Why shouldn't the platform know about the damage region in a swap, if
>> it's available?  It looks like it was successfully used for Android, and
>> we should be using it for Present as well.
>
> From the spec [1], the damage region referred to by partial_update spec is
> the damaged part of the buffer when it is used again. The damage that the
> compositor/platform needs to know is the damage between the (n-1)th
> frame and the nth frame. Quoting from the spec:
> "   The surface damage for frame n is the difference between frame n and frame
>     (n-1), and represents the area that a compositor must recompose."
> This is the damage referred to by the swap_buffers_with_damage spec [2],
> whereas the partial_update damage region's objective is to restrict the subsequent
> rendering operations on the back buffer, to only those regions which have changed since
> that buffer was last used. This information is available as the buffer
> age. Some more information: [3].

OK, let's document that in the new internal API you're adding then.
Things I'd want to know as an implementer of the hook:

1) Am I guaranteed that it's called before the frame is started?

2) Is the behavior if the client draws outside of the partial update
damage region defined?  (is it "the driver must not change pixels
outside of the partial region" or "the driver might not change pixels
outside of the partial region")

3) Is the client guaranteed to fully initialize pixels in the partial
update region, or might it depend on previous contents?
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