D20521: Don't rescale every output every time outputs change

apol added inline comments.

INLINE COMMENTS

> davidedmundson wrote in drm_backend.cpp:517
> If we have the hasKey() check, then I don't understand why we also need to use a 0 as a special value for defining unset.

Because otherwise the window appears like uninitialized in practice, otherwise. This way we make sure that at least once the function is called.

::setScale does quite some calls under the hood.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D20521

To: apol, #plasma
Cc: davidedmundson, ngraham, kwin, jraleigh, GB_2, mkulinski, ragreen, jackyalcine, Pitel, iodelay, bwowk, ZrenBot, alexeymin, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart