Rethinking options and solutions I think it is the time to solve permanently the Plasma Theme Background issues.
Plasma Theme Backgrounds have the following important issues:
I.1. Because plasma theme background transparency can not be altered by the user the plasma theme designers choose one transparency level to rule them all
I.2. Background outline settings can not be specified by the user so it is up the designer decision to provide or not
Current situation in Latte:
Latte provides a transparency level for the panel background from 0% - DESIGNER_SET% that means maybe full solidness may never be possible if BLUR is not enabled. This is why Latte provides the SolidStyle option in order that instead of the translucent background, Latte will use the solid one that is used in Plasma !compositing mode. Of course this creates the following strange situations:
T.1. SHADOWS are not specified for solid background in !compositing mode, Latte is just drawing those from the translucent one case
T.2. When OUTLINE is set inside the plasma theme background and the user has choose 0% opacity in combination with BLUR effect then a separation appears between the BLUR and the SHADOWS
Solutions:
S.1. The SolidStyle case will be dropped totally
S.2. Latte will provide an OUTLINE Option for the background to be drawn above the Plasma theme. The user will be able to set only its size. The OUTLINE color will be calculated automatically by Latte in order to fit in with the plasma theme and the LATTE COLORS which are provided from SMART setting and WINDOW SCHEMES
S.3. Latte will provide a heuristic for its PlasmaThemeExtended class in order to discover what is the transparency used in the panel background from the current plasma theme
S.4. Latte will draw a second background behind the Plasma Background that will help to provide always 0%-100% opacity... Meaning 0% full transparent – 100% full solidness
S.5. For the case that a gap appears between the BLUR and the SHADOWS the user should be able to activate OUTLINE in order to fill it