How to draw triangle and rhombus shapes using QT

Question

I need to draw triangle shape and rhombus shapes like this image.In this code which design triangle shape (figure 1) but I need to add this shape to text "TRI" . And I also need to implement this code to design rhombus shape like (figure 2). please help me to solve this.

Figure 1

void MainWindow::on_btnTri_clicked()
{
    QPen redPen(Qt::black);
    redPen.setWidth(2);
    QRectF rect = QRectF(0, 0, 200, 200);

    QPainterPath path;
    path.moveTo(rect.left() + (rect.width() / 2), rect.top());
    path.lineTo(rect.bottomLeft());
    path.lineTo(rect.bottomRight());
    path.lineTo(rect.left() + (rect.width() / 2), rect.top());
    QGraphicsPathItem* item = ui->graphicsView->scene()->addPath(path, redPen);
    item->setFlag(QGraphicsItem::ItemIsMovable, true);
    item->setFlag(QGraphicsItem::ItemIsSelectable,true);
}

Figure 2 I use this code to design figure 2 But which cannot pass parameters to change there size,My figure 1 designed code I can able pass two parameters to QRectF(0, 0, para1, para2); this for change triangle's size.so I need to change this code to do the same thing using QPainterPath or any other way.

void MainWindow::on_btnRomb_clicked()
{
    QPolygonF romb;
    romb.append(QPointF(20,40));
    romb.append(QPointF(0,20));
    romb.append(QPointF(20,0));
    romb.append(QPointF(40, 20));
    QGraphicsPolygonItem* itemR = ui->graphicsView->scene()->addPolygon(romb);
    itemR->setFlag(QGraphicsItem::ItemIsMovable);
}

Answer 1

you must use the addText() method of QPainterPath, to place it in the center you must calculate the width and height of the text for it QFontMetrics is used:

QPen redPen(Qt::black);
redPen.setWidth(2);
QRectF rect(0, 0, 200, 200);

QPainterPath path;
path.moveTo(rect.left() + (rect.width() / 2), rect.top());
path.lineTo(rect.bottomLeft());
path.lineTo(rect.bottomRight());
path.lineTo(rect.left() + (rect.width() / 2), rect.top());
path.moveTo(rect.center());

QFont font("Times", 20, QFont::Bold);

QFontMetrics fm(font);
QString text = "TRI";
QSize size = fm.size(Qt::TextSingleLine, text);
path.addText(rect.center()+ QPointF(-size.width()*0.5, size.height()*0.5), font, text);

QGraphicsPathItem *item = ui->graphicsView->scene()->addPath(path, redPen);
item->setFlag(QGraphicsItem::ItemIsMovable, true);
item->setFlag(QGraphicsItem::ItemIsSelectable,true);

For the case of the diamond you should only get the midpoints of each vertex:

QPainterPath path;
QRectF rect(0, 0 , 100, 100);
path.moveTo(rect.center().x(), rect.top());
path.lineTo(rect.right(), rect.center().y());
path.lineTo(rect.center().x(), rect.bottom());
path.lineTo(rect.left(), rect.center().y());
path.lineTo(rect.center().x(), rect.top());
QGraphicsPathItem* itemR = ui->graphicsView->scene()->addPath(path);
itemR->setFlag(QGraphicsItem::ItemIsMovable);