[Interest] Background Color of QPdfView

[Joshua Grauman]

Thanks, I should have thought to look in the code, but that's 
straightforward enough. I'm with you, I don't think it should use QPalette 
because the default should definitely be white regardless of whether or 
not you are using dark mode. I'm thinking separate functions to set/get 
the background color would be best. It seems most pdf viewers have an 
option to change the background color for accessibility, so that seems 
like a reasonable option. I'll suggest it. The change would be fairly 
easy.

Josh

> void QPdfView::paintEvent(QPaintEvent *event)
> {
>     Q_D(QPdfView);
> 
>     QPainter painter(viewport());
>     painter.fillRect(event->rect(), palette().brush(QPalette::Dark));
>     painter.translate(-d->m_viewport.x(), -d->m_viewport.y());
> 
>     for (auto it = d->m_documentLayout.pageGeometryAndScale.cbegin();
>          it != d->m_documentLayout.pageGeometryAndScale.cend(); ++it) {
>         const QRect pageGeometry = it.value().first;
>         if (pageGeometry.intersects(d->m_viewport)) { // page needs to be painted
>             painter.fillRect(pageGeometry, Qt::white);
> 
> So the answer for now is no.  You can write up a suggestion on bugreports.qt.io if you want.  Perhaps the page background should use a palette color.  But then, dark mode would be problematic, wouldn't it?
>  If the page background is dark, and the PDF also has dark text, we’d get a bug report right away, now that dark mode is popular.  
> 
> I also hate trying to read bright-white PDFs in dark rooms when I’m trying to have most of the onscreen content be dark.  It can make my eyes go into a weird mode where I see jagged-edged round-ish rainbows
> for a while, and can’t read anything for a few minutes.  (Does anybody know what that’s called?)  But PDF is a simulation of paper.. and paper is usually white, so the content usually has dark text.  In
> another PDF viewer, I once tried to solve that problem with a shader.  (That’s also tricky: you want to only replace the background color itself, and the main text color, which is likely black but perhaps
> not.  So the fragment shader can invert any color that is a shade of grey, but leave the rest as they are.  And often it will work well enough, but not always.) It’s just that if we shipped such a feature,
> there would probably be more bug reports, I suppose.
> 
> It’s easier in Qt Quick though.  Image { source: “file.pdf”; currentFrame: 5 } will give you page 5 (starting from 0, so probably page 6) with no background at all (unless the PDF does its own background
> fill): whatever is behind it will show through.  (Window is white by default though.)  The packaged viewer components are much more complex than that, of course.  You can experiment by forking one of those
> QML files (depending whether you want to scroll through all the pages, or just one page at a time).  https://code.qt.io/cgit/qt/qtwebengine.git/tree/src/pdfquick
>
>       On Dec 5, 2024, at 00:58, Joshua Grauman <jnfo-d at grauman.com> wrote:
> 
> Hello,
> 
> I generate pdfs by using QPainter to paint onto a QPrinter. My understanding is that the generated pdf has a transparent background, even though most viewers view the pdf with a white background. I am
> able to view the pdf with a different color background with Okular for example. I'm wondering if there is any way to change the background color of QPdfView (to black)? I tried changing the palette of
> QPdfView or change it's style sheet but those didn't do it. Does anyone know if there is any way to display the pdf with a different background color using QPdfView?
> 
> Josh
> 
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