Create a transition between SDDM and Plasma according tot he following mockup and specification:
Ksplash is removed in favour for two clear effects, one is the "fade to
desktop" already present in Kwin, the other is an effect where SDDM fades in a
very specific way. (the SDDM interface fades leaving only the chosen logged in
users avatar fading slightly slower (can be seen in the thumbnail gif named
"SDDMfade")
Essentially SDDM fades, and then directly as part of it visually, a fade to
desktop.
[future ideas: this animation, the slowness of the fade of the SDDM interface,
the avatars fade may be tweaked slightly in the future, a shift in how the
other avatars disappear as well with some movement planned as can be seen in
earlier mockups. The reason for this not being present now is that its very
tricky to get 1-to-1 exactness with animations and the more details the less
exactness]
Critical Notes #1: if this handoff between SDDM and Ksplash is impossible for
technical reason or will stutter another plan must be drawn up. The goal here
is speed - if speed can be improved by having the animation SOLELY in SDDM and
ignoring Ksplash then that is better.
For this reason we need technical input and help testing.
Critical Notes #2: The SDDM theme can switch wallpaper, the wallpaper being
the LAST thing seen in combination with the logged in users avatar - its
relevant that the this work if the user switch wallpaper so that the wallpaper
is the last seen instead of "stock blue".
If a nice shift between desktop, where SDDM fades (see Ksplash below too)
isn't possible, then we propose a temporary solution where SDDM fades quickly
to black and have just a fade from black effect again in Ksplash (or handled
entirely by Kwin as Ksplash seems not as relevant on many systems and just
percieved as a delay). It really does depend on the technical feasiblity and
the work it would require.