UI color palettes vs. document color palettes

[Friedrich W. H. Kossebau]

Hi,

I am currently looking into fixing the conflict of the character/paragraph 
preview rendering e.g. in the paragraph style selection combobox (see 
attachment), which shows most with dark UI color schemes.

Who else has looked into that before or is perhaps looking right now or plans 
to do so?

One reason I see in the member KoTextDocumentLayout::PaintContext::textContext 
of type QAbstractTextDocumentLayout::PaintContext, which seems nowhere 
explicitely initialized, thus keeps as values "the application's default 
palette" (cmp. API dox). Which can result in non-compatible mixing of the 
document colors and the UI colors.

E.g. in "KoTextLayoutArea::paint(...)" for styles that have no color set for 
the text the text color as set for the UI is used -> fail for dark UI schemes.
--- 8< ---
    painter->setPen(context.textContext.palette.color(QPalette::Text)); // for 
text that has no color.
--- 8< ---

Similar in "TextShape::paintComponent(...)" for hightlighting the palette is 
actually the one of the UI... which kind of makes sense here, okay.
--- 8< ---
    KoTextDocumentLayout::PaintContext pc;
    [...]
    QPalette palette = pc.textContext.palette;
    selection.format.setBackground(palette.brush(QPalette::Highlight));
    selection.format.setForeground(palette.brush(QPalette::HighlightedText));
    pc.textContext.selections.append(selection);
--- 8< ---

>From what I understood the flag "UseWindowFontColor" is also just resulting in 
black or white, depending on the luma of the effective background, but never 
the UI colors, right? Hm, that is actual an error in 
KoTextLayoutArea::paint(...), "the window foreground color should be used as 
the foreground color for a light background color", not black (20.385 
style:use-window-font-color). Which again will be a problem with dark UI color 
schemes, which might need the inverse treatment, i.e. if the difference of the 
luma is too low, then black should be used.

Still, what to do in the case that flag is not set? What should be used for 
the background in the style preview in general?
The color of the current shape?
The color of the page?

What if the background is not a simple color, but something more complicated?

And I still am curious why KoTextLayoutArea::paint(...) renders the text in 
black on the document, when it uses the UI text color if called from 
KoStyleThumbnailer, for the same paragraph/character style.

Cheers
Friedrich
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