Introducing transparent colors

[Yokota K.]

> 2026/05/20 20:50、Koji Yokota <yokota6 at gmail.com>のメール:
> 
>> 2026/05/18 22:10、Jean-Marc Lasgouttes <lasgouttes at lyx.org>のメール:
>> 
>> I welcome proper support for transparent colors, although we will have to check that our drawing mechanism is ready for it. I suspect that there are some implicit assumptions of opacity here and there.
> 
> I understand the concern about the risk. The only entrance to RGBA-related representation is via 9-chars ARGB strings (#AARRGGBB) given by QColor::name(QColor::HexArgb) in GuiPrefs.cpp. The user’s theme color settings come in here. Then modified Color::rgbFromHexName() converts it to RGBAColor class, a subclass of GBAColor.
> 
> Modified Color::X11hexname() can output 9-chars ARGB strings when arg is RGBAColor class but it is limited to UI theme colors, since other colors will not be represented by RGBAColor.
> 
> So it forms a closed system like:
> 
>        Color setting in Preferences
>                      |
>                 (QColor::name)
>                      |
>                      V
>                  #AARRGGBB ——— Color::rgbFromHexName() ——> RGBAColor (RGBColor
>                      ^                                        |       subclass)
>                      |———————— Color::X11hexname() <———————————
> 
> Existing functions use the base class RGBColor so they are not affected.
> 
> # BTW I should rename the RGBAColor struct to ARGBColor.
> 
>> For you preedit needs, are you aware of the mergeColor mechanism in the Color class? I understand it is a kludge, though.
> 
> Thank you for the information. I haven’t checked it but it can be an alternative if the above doesn’t go well.

If there is no objection, I’m going ahead with ARGBColor. It can use a ready-made color dialog so we can refrain from setting up a customized switch in UI for the interpretation of white between transparency and solid white.

Koji
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