Transparency and the unified header

#Following the transparency settings

The Transparency section of System Settings → Desktop Style → Configure Desktop Style… sets how see-through panels, pop-ups, tooltips and desktop widgets are. It works like accent colors: one desktop-wide setting, applied to every desktop style that asks for it. Styles that don't ask keep their own transparency.

A style asks for it with one line in its colors file, next to FollowAccentColor:

[General]
FollowAccentColor=true
FollowDesktopThemeOpacity=true

The settings live in kdeglobals:

[DesktopThemeOpacity]
Enabled=true
Panels=70
Popups=85
Tooltips=85
Widgets=80

Values are percent. A missing key uses the default shown here. With Enabled=false (the default), or in a style without FollowDesktopThemeOpacity=true, nothing changes.

#Marking the see-through parts

SonicDE adds one CSS rule per surface to the stylesheet it puts into every theme SVG, next to the .ColorScheme-… color rules:

Give the class to each see-through fill, next to its color class, and put the style's own opacity in the opacity attribute:

<rect id="rect4138" style="fill:currentColor" opacity="0.85"
      class="ColorScheme-Background SonicOpacity-Popup" width="32" height="32" />

• Never put that opacity inside style="". An inline style wins over the generated rule, so the setting would have no effect. Measured with Qt 6.11.3: opacity="0.75" with a 0.25 rule draws at 0.25; style="opacity:0.75" with the same rule stays at 0.75.
• The file needs the <style id="current-color-scheme"> element (see System and accent colors); the rules are only added to files that have it.
• Tag the plain files and the translucent/ ones. The desktop shell uses translucent/ when the blur effect is on, the plain files when compositing is on without blur, and opaque/ without compositing. Leave opaque/ alone.
• Only tag the fills. Edge highlights, shadows (shadow-*), masks (mask-*) and hints keep their values.
• Without the setting, the attribute is used and the style looks exactly as before.

The default and Silver themes in sonic-interface-libraries show the full set.

#The unified header

#Pop-up headings

A pop-up's header and footer, such as the search bar and the buttons along the bottom of the application launcher, are drawn from widgets/plasmoidheading, on top of the pop-up's background. To keep them as see-through as the rest of the pop-up, the heading draws no fill, only its separator lines (ColorScheme-Frame): give the fill paths opacity="0" and keep the elements, so the frame sizes and margins stay the same. Any fill there would stack on the pop-up's own and look more solid.

#Window decorations

The titlebar and the toolbars and menu bars under it can be one see-through surface, the tools area. Its settings are shared desktop-wide in the [ToolsArea] group of kdeglobals, set in Window Decorations → Configure Titlebar…, and read through KToolsArea in sonic-frameworks-color-scheme by the decoration, the app style and the Qt Quick platform integration.

A window decoration that draws a see-through titlebar from these settings says so in its plugin metadata:

{
    "KPlugin": { "Name": "Silver" },
    "X-SonicDE-ToolsArea": true
}

When SonicWin loads a decoration without it, it turns the tools area off (Enabled=false) and records that it did (DisabledByDecoration=true), so toolbars don't stay see-through under a solid titlebar. When it loads a decoration with the marker, it turns a tools area it turned off back on. A tools area the user turned off stays off.