[cairo-bugs] [Bug 88203] New: Replaying recording surfaces with OVER has far worse performance than when using the SOURCE operator

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=88203

            Bug ID: 88203
           Summary: Replaying recording surfaces with OVER has far worse
                    performance than when using the SOURCE operator
           Product: cairo
           Version: 1.12.16
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: general
          Assignee: chris at chris-wilson.co.uk
          Reporter: emanuele.aina at collabora.com
        QA Contact: cairo-bugs at cairographics.org

I have some code that collects some partial redrawing of a surface in a
recording surface and then later replays it on the target surface.

I've noticed that when using the OVER operator the replay is surprisingly slow,
ie. the overhead over painting directly on the target is noticeable.

When using the SOURCE operator things get back to my expectations and the
overhead is negligible, but unfortunately the SOURCE operators clears the
target surface, destroying all the areas that don't get redrawn and thus making
it unfit for my purposes.

I'd like to have a way to replay the recording surface without any clearing and
without any intermediate surface.

Shouldn't the OVER operator do that? In what cases replaying directly on the
target would differ from replaying to an intermediate surface and composite it
with OVER?

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