QTreeView color of painted row - qt

Question

I extented a QStyledItemDelegate to draw some pixmaps on the right side of a QTreeView. This works well, however, I realized that the pixmaps can be in front of the text if it gets too long.
So I tried to draw a rectangle of the same color as the background before drawing my pixmap.
void MyItemDelegate::paint(
QPainter *painter,
const QStyleOptionViewItem &option,
const QModelIndex &index) const
{
...
QStyledItemDelegate::paint(painter, option, index);
...
QStyleOptionViewItem opt = option;
initStyleOption(&opt, index);
...
painter->fillRect(rect, opt.backgroundBrush);
painter->drawPixmap(topLeft, pixmap);
}
I know that all variables are correct except opt.backgroundBrush. It's always invisible black, with or without the initStyleOption call.
Then I started to check the value of opt.state and opt.features to pick the color myself. I had some success with the alternating color (QStyleOptionViewItem::Alternate) but it's starting to get long and tedious because there are other states (hover and selected) and other OS that may have other states. There must be a simpler way.
So, my question is: How can I get the actual color that will be used to paint the row when I'm in the paint method? Or, do you have any other clean way to avoid this situation?

Answer 1

As suggested by #G.M. I used the QItemDelegate class instead of QStyledItemDelegate and I do have more control on the drawing process. Notably because of the added protected functions like drawDisplay. Overriding this method, I can adjust the "display rectangle" to a smaller size than what was calculated by Qt.
void ActionsItemDelegate::drawDisplay(
QPainter *painter,
const QStyleOptionViewItem &option,
const QRect &rect,
const QString &text) const
{
const int minX = ...; // x position of the left-most icon
const int iconsWidth = rect.width() - (minX - rect.x());
QItemDelegate::drawDisplay(painter, option, rect.adjusted(0, 0, -iconsWidth, 0), text);
}
The drawback is that the UI changes when using QStyledItemDelegate. I don't know how to get the benefits of both: normal style and more controls.

Answer 2

I may process differently. I won't start by calling:
QStyledItemDelegate::paint(painter, option, index);
in the first place.
Then, the important part: if you know how much icons there are on your items, you could calculate the bounding rectangle.
How do you know how many icons you have ? Maybe by calling something like:
bool hasIcon = index->data(YourAPP::HasIcons).toBool();
You could have something like this in your delegate:
void MyItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const {
...
QStyleOptionViewItem o = option;
initStyleOption(&o, index);
bool hasIcon = index->data(YourModel::HasIcons).toBool();
// or
bool hasCustomRole1 = index->data(YourModel::Role1).toBool();
bool hasCustomRole2 = index->data(YourModel::Role2).toBool();
if (hasIcon) {
// width of your icons, can be like o.rect.height() * numbers of icons
int width = 0;
// shrink your first rectangle
o.rect.adjust(0, 0, -width, 0);
// create a second rectangle
QStyleOptionViewItem o2 = option;
initStyleOption(&o2, index);
o2.rect.adjust(width, 0, 0, 0);
// paint your icons
...
painter->drawPixmap(o2, pixmap);
} else {
QStyledItemDelegate::paint(painter, option, index);
}