Retrieve the colours used by Qt to render a frame of StyledPanel shape

[agarny]

I have a widget of my own and I would like to ensure that the colours I use are consistent with the rest of the widgets I use in my Qt application. For what I am doing, I would need to retrieve the colours used by a frame which shape is set to QFrame::StyledPanel. On my copy of Windows 7, Qt renders the border of such a frame using a colour which RGB value is (130, 135, 144). Now, in my widget, I would like to use that colour, but I can't seem to be able to get it. I tried to get the colour from my widget's palette by using the color() function and passing to it different colour roles (QPalette::Window, QPalette::WindowText, etc.), but none of them gave me the RGB value used by Qt to render the frame above. So, what am I missing?...

Cheers, Alan.

[ChiliPalmer]

Hi,

depending on the style, not everything is drawn by Qt itself, but by the native style engine. So some Colors etc. are impossible to get.
I had the same issue as you and tried just letting the style draw the frame, which worked fine. But as I only needed part of a frame, I just used the color you mentioned to draw the frame myself.
I guess those are your two options as well

[agarny]

Well, at this stage, I just need to use the colour I mentioned (even though I would like a more general approach to my problem, if possible), so how did you get it in the end?

[ChiliPalmer]

I just took a look at the code, as I still would like to get that color as well. But as I said, the frame is drawn by the windows style engine. So no chance getting the color.
As I said, I just draw the frame with the color you mentionend myself.

[Lykurg]

I don't know what you want to do with that color exactly, but with QStylePainter (or QStyle direct) you can draw frames etc. according to the current style.

[agarny]

As I said, I just draw the frame with the color you mentionend myself.

Ah, so you are really using (130, 135, 144)...?! Ok, that's not something I want to do. I want my applicaiton to be able to respond to a change of system colour theme, if needed.

I don't know what you want to do with that color exactly, but with QStylePainter (or QStyle direct) you can draw frames etc. according to the current style.

I just want to be able to use the colour used by Qt to render other widgets, so that it's all consistent colour wise. Anyway, I have never tried QStylePainter, so I will have a look at it, thanks.

[agarny]

Ok, for those interested, I have 'solved' my problem by doing the following:

static bool firstTime = true;
static QColor borderColor = QColor();
 
if (firstTime) {
    QFrame frame;
    QImage image = QImage(widget->size(),
                          QImage::Format_ARGB32_Premultiplied);
 
    frame.setFrameShape(QFrame::StyledPanel);
    frame.render(&image);
 
    borderColor = QColor(image.pixel(0, 0));
 
    firstTime = false;
}

static bool firstTime = true;
static QColor borderColor = QColor();

if (firstTime) {
    QFrame frame;
    QImage image = QImage(widget->size(),
                          QImage::Format_ARGB32_Premultiplied);

    frame.setFrameShape(QFrame::StyledPanel);
    frame.render(&image);

    borderColor = QColor(image.pixel(0, 0));

    firstTime = false;
}

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[wysota]

What if the pixel happens to be transparent in this particular theme? What if the user changes the theme during the life of the program? What if...?

[agarny]

What if the pixel happens to be transparent in this particular theme? What if the user changes the theme during the life of the program? What if...?

I complete agree that this is not perfect, hence my use of single quotes around my use of "solved". So, if anyone has a better solution, then please feel free to share it with me. In fact, I just wish that Qt would provide us with more information about the colour scheme used to render various widgets.

[wysota]

Qt doesn't have anything to do with this. It's not Qt that renders the theme on Windows Vista and up. You can probably use the native API to ask for that colour if the theming API supports it. Qt reports all it can in QPalette. If the colour you are looking for is not there then all that is left is Windows theming API.

[agarny]

I appreciate that Qt has nothing to do with it, but all I am trying to do is to have my widget using colours that are consistent with the other widgets that are (indirectly) rendered by Qt. Also, I want this to work on Windows, Linux and Mac OS X. So, for now, the solution I have is far from perfect, but it's still better than nothing (I could however improve it to at least address the change of theme during the life of the application).