Reimplementing QStyledItemDelegate::paint - How to obtain subelement coordinates? - c++

Question

A QTreeView is rendered with the help of a custom QStyledItemDelegate::paint method. The intention is to add graphical elements to the nodes, e.g. to draw (and fill) a box around the item texts. The tree items may have check boxes, or not.
The Ruby code below achieves the goal, except that I cannot obtain the coordinates of the text element. An empirical offset (x=29; y=4) serves as a workaround. The super method draws the text on top of the box.
How can I obtain the coordinates of the text element?
Is this the right approach at all, or do I have to use drawText and drawControl instead of calling the superclass paint method? In that case, how do you control the layout of the sub elements?
(This question is not Ruby specific. Answers containing C++ are welcome.)
class ItemDelegate < Qt::StyledItemDelegate
def paint(painter, option, index)
text = index.data.toString
bg_color = Qt::Color.new(Qt::yellow)
fg_color = Qt::Color.new(Qt::black)
offset = Qt::Point.new(29,4)
painter.save
painter.translate(option.rect.topLeft + offset)
recti = Qt::Rect.new(0, 0, option.rect.width, option.rect.height)
rectf = Qt::RectF.new(recti)
margin = 4
bounding = painter.boundingRect(rectf, Qt::AlignLeft, text)
tbox = Qt::RectF.new(Qt::PointF.new(-margin,0), bounding.size)
tbox.width += 2*margin
painter.fillRect(tbox, bg_color)
painter.drawRect(tbox)
painter.restore
super
end
end
Edit: Please find a self-contained example here in this Gist.

Answer 1

I had the same problem in C++. Unfortunately, the workaround on option.rect.* properties seems to be the only way to find the text coords.
Here the paint method of my delegate:
void ThumbnailDelegate::paint(QPainter *p_painter, const QStyleOptionViewItem &p_option, const QModelIndex &p_index) const
{
if(p_index.isValid())
{
const QAbstractItemModel* l_model = p_index.model();
QPen l_text_pen(Qt::darkGray);
QBrush l_brush(Qt::black, Qt::SolidPattern);
/** background rect **/
QPen l_pen;
l_pen.setStyle(Qt::SolidLine);
l_pen.setWidth(4);
l_pen.setBrush(Qt::lightGray);
l_pen.setCapStyle(Qt::RoundCap);
l_pen.setJoinStyle(Qt::RoundJoin);
p_painter->setPen(l_pen);
QRect l_border_rect;
l_border_rect.setX(p_option.rect.x() + 5);
l_border_rect.setY(p_option.rect.y() + 5);
l_border_rect.setWidth(p_option.rect.width() - 16);
l_border_rect.setHeight(p_option.rect.height() - 16);
QPainterPath l_rounded_rect;
l_rounded_rect.addRect(QRectF(l_border_rect));
p_painter->setClipPath(l_rounded_rect);
/** background color for hovered items **/
p_painter->fillPath(l_rounded_rect, l_brush);
p_painter->drawPath(l_rounded_rect);
/** image **/
QPixmap l_pixmap = bytearrayToPixmap(l_model->data(p_index, ImageRole).toByteArray()).scaled(150, 150, Qt::KeepAspectRatio);
QRect l_img_rect = l_border_rect;
int l_img_x = (l_img_rect.width()/2 - l_pixmap.width()/2)+l_img_rect.x();
l_img_rect.setX(l_img_x);
l_img_rect.setY(l_img_rect.y() + 12);
l_img_rect.setWidth(l_pixmap.width());
l_img_rect.setHeight(l_pixmap.height());
p_painter->drawPixmap(l_img_rect, l_pixmap);
/** label **/
QRect l_txt_rect = p_option.rect;
l_txt_rect.setX(l_border_rect.x()+5);
l_txt_rect.setY(l_border_rect.y() + l_border_rect.height() -20);
l_txt_rect.setHeight(20);
l_txt_rect.setWidth(l_txt_rect.width()-20);
QFont l_font;
l_font.setBold(true);
l_font.setPixelSize(12);
p_painter->setFont(l_font);
p_painter->setPen(l_text_pen);
QString l_text = l_model->data(p_index, TextRole).toString();
p_painter->drawText(l_txt_rect, Qt::ElideRight|Qt::AlignHCenter, l_text);
}
else
{
qWarning() << "ThumbnailDelegate::paint() Invalid index!";
}
}
I am not skilled on Ruby but, as you can see, I am using drawPath, drawPixmap and drawText.
Here is the result:
I think it is better to avoid invoking paint from the superclass, since it should be done automatically by Qt and you may break something on the UI lifecycle.