Custom drawing of a QSlider (Qt)

Question

I want to intercept the QPaintEvent on a QSlider and draw it. But I can not find the details on the geometry of the thing. I can know the rect() of the whole widget but how can you tell the position of first tickmark or the last one in the widget's rectangle? (there's a margin at left and right of the tracking channel). Or the rectangle of the "handle"?

Answer 1

Thanks for the hints in the replies. After some investigation this seems to work. For the case if it is of use to someone:

QStyleOptionSlider opt;
slider->initStyleOption(&opt);

QStyle *styl=style();
Rect rectHandle=styl->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderHandle, NULL);
Rect rectGroove=styl->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderGroove, NULL);

int avl=styl->pixelMetric(QStyle::PM_SliderSpaceAvailable, &opt, this); // width in an horizontal slider of the groove (width of widget - margins)

Answer 2

Are you shure that you want to reimplement a paint event?
May be it will be enough to wryte a custom style sheet?
Here is an example for qslider from doks:

 QSlider::groove:horizontal {
     border: 1px solid #999999;
     height: 8px; /* the groove expands to the size of the slider by default. by giving it a height, it has a fixed size */
     background: qlineargradient(x1:0, y1:0, x2:0, y2:1, stop:0 #B1B1B1, stop:1 #c4c4c4);
     margin: 2px 0;
 }

 QSlider::handle:horizontal {
     background: qlineargradient(x1:0, y1:0, x2:1, y2:1, stop:0 #b4b4b4, stop:1 #8f8f8f);
     border: 1px solid #5c5c5c;
     width: 18px;
     margin: -2px 0; /* handle is placed by default on the contents rect of the groove. Expand outside the groove */
     border-radius: 3px;
 }

Answer 3

Have you considered using setStyleSheet instead ? If you really want to draw it yourself, you can have a look at how it's done in Qt source code: qt/src/gui/widgets/qslider.cpp