D18000: Tweak slidingpopups effect to make animation smoother and more consistent

zzag added inline comments.

INLINE COMMENTS

> slidingpopups.cpp:141
>          if (slideLength < geo.width()) {
> -            data.multiplyOpacity(t);
> +            data.multiplyOpacity(interpolate(0.0, 1.0, t));
>          }

`data.multiplyOpacity(t)` and `data.multiplyOpacity(interpolate(0.0, 1.0, t));` do the same thing. Could you please revert this change?

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D18000

To: ngraham, #vdg, zzag, #kwin, sefaeyeoglu
Cc: niccolove, ngraham, abetts, davidedmundson, zzag, kwin, LeGast00n, The-Feren-OS-Dev, sbergeron, jraleigh, zachus, fbampaloukas, GB_2, mkulinski, ragreen, jackyalcine, iodelay, crozbo, bwowk, ZrenBot, alexeymin, himcesjf, lesliezhai, ali-mohamed, hardening, romangg, jensreuterberg, sebas, apol, ahiemstra, mart