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

Harish Krupo harish.krupo.kps at intel.com
Wed Jul 11 17:24:33 UTC 2018

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].

[1] https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_partial_update.txt
[2] https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_swap_buffers_with_damage.txt
[3] https://community.arm.com/graphics/b/blog/posts/mali-performance-3-is-egl_5f00_buffer_5f00_preserved-a-good-thing

Thank you
Harish Krupo

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