Bug 504998

SUMMARY

I was looking to implement customising an aurorae theme using the current titlebar colour. I had a specific usecase, but from google, it seems it is a repeatedly-asked question, if it's possible to customise accent colours for window decorations on a per-application basis.

In my system settings, the colour themes support various properties, including specific ones for the titlebar text and background, in additopon to the more general button.text colours. After going down a few rabbitholes in Aurorae, and form the documentation [here](https://develop.kde.org/docs/plasma/aurorae/#package-structure) on Aurorae themes, and the linked page [here](https://develop.kde.org/docs/plasma/theme/theme-colors/#system-colors) on using colour theme variables within Plasma, it seems that the first blocker is that the KSVG doesn't expose all of the colours that are available in the theme files.

I can get my decorations to use one of the system colours by adding CSS styles to the aurorae SVG as in the link above like so:
```CSS
      .ColorScheme-Highlight
      {
          color:#ff3cef; /* plceholder that will be replaced by the KSVG engine */
      }

      .ColorScheme-ActiveTitlebar {
          color:#ff3cef; /* plceholder that will be replaced by the KSVG engine */
      }
    </style>
    <path 
```

However here, using Highlight renders okay; trying to use the titlebar colours does not. That makes sense as [this enum](https://invent.kde.org/frameworks/ksvg/-/blob/917abf3e057fb83e1384a0f2b53e641fbe4ffaa1/src/ksvg/svg.h#L167
) (this may not be the canonical/correct location, just using Gitlab's search function) doesn't list anything referencing titlebars. I can only assume that themes implemented in code, such as breeze, are accessing a colour theme class directly, and so sidestep this issue and thus support custom titlebar colours, or else it;s handled differently in KWin somewhere.

Whilst for general-purpose theming of SVGs (which it would seem KSVG does, being modular), using the titlebar colours in those files might be a bit of an abuse, I'd like to ask if people owuld ocnsider it appropriate to expose them, as I think the possibilities it opoens up with Aurorae would be quite significant. Aurorae supports themes in native code, QML, and SVG, althogh the SVG form has more limited support - yet from what I can find is by a long shot the format most used by designers and theme authors. To implement what I am looking to do, I could mangle something using a different element in the theme, but the titlebar colour is purposed exactly for that, and there would be other side-effects in how the window contents are drawn, so it makes sense to me that Aurorae should have access to it when working with SVGs.

The colour theme is also exposed by the KWin Scripting API, so having access to this property in a theme would allow scripts and addons to set window decoration colours dynamically, assigning different colours to windows based on application class or state, where currently it is limited to shading, active/inactive, etc. And a few changes ot Aurorae might be needed (haven;t investigated that fully yet), but in either case it should then be as simple as using the new styles in the SVGs for a theme and having any dynamic behaviour propagate through automatically to theme SVGs that are aware of these colours.

So seems like a quick change and I oculd open an FR on invent when I have time, but thought I should raise the question first in case there would be objections or repercussions.

Cheers




EXPECTED RESULT


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION