如何将QPainter drawText对齐一个点而不是一个矩形？

Question

我想使用一个点作为坐标而不是矩形来设置文本绘图对齐.

据我所知QPainter::drawText,只有当我将坐标作为矩形传递时才允许设置文本对齐.

如果我希望相对于某个点而不是矩形对齐文本,如何设置文本对齐？

Answer 1

当您传递绘制文本的起点时,您实际上是在一个大的矩形上绘制文本,该矩形在给定点处具有左下角.所以你需要的是根据你的起点和选择的对齐方式提供一个合适的"无限"矩形:

// https://github.com/KubaO/stackoverflown/tree/master/questions/alignments-24831484
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif

void drawText(QPainter & painter, qreal x, qreal y, Qt::Alignment flags,
              const QString & text, QRectF * boundingRect = 0)
{
   const qreal size = 32767.0;
   QPointF corner(x, y - size);
   if (flags & Qt::AlignHCenter) corner.rx() -= size/2.0;
   else if (flags & Qt::AlignRight) corner.rx() -= size;
   if (flags & Qt::AlignVCenter) corner.ry() += size/2.0;
   else if (flags & Qt::AlignTop) corner.ry() += size;
   else flags |= Qt::AlignBottom;
   QRectF rect{corner.x(), corner.y(), size, size};
   painter.drawText(rect, flags, text, boundingRect);
}

void drawText(QPainter & painter, const QPointF & point, Qt::Alignment flags,
              const QString & text, QRectF * boundingRect = {})
{
   drawText(painter, point.x(), point.y(), flags, text, boundingRect);
}

int main(int argc, char *argv[])
{
   QApplication a{argc, argv};
   QLabel label;
   QPicture pic;
   pic.setBoundingRect({-100, -100, 200, 200});
   QPainter p(&pic);
   const QPointF pt;

   p.drawEllipse(pt, 3, 3);
   p.setFont({"Helvetica", 40});
   p.setPen({128, 0, 0, 128});
   drawText(p, pt, Qt::AlignBottom, "_LB");
   drawText(p, pt, Qt::AlignVCenter, "_LC");
   drawText(p, pt, Qt::AlignTop, "_LT");
   p.setPen({0, 128, 0, 128});
   drawText(p, pt, Qt::AlignBottom | Qt::AlignHCenter, "MB");
   drawText(p, pt, Qt::AlignVCenter | Qt::AlignHCenter, "MC");
   drawText(p, pt, Qt::AlignTop | Qt::AlignHCenter, "MT");
   p.setPen({0, 0, 128, 128});
   drawText(p, pt, Qt::AlignBottom | Qt::AlignRight, "RB_");
   drawText(p, pt, Qt::AlignVCenter | Qt::AlignRight, "RC_");
   drawText(p, pt, Qt::AlignTop | Qt::AlignRight, "RT_");
   p.end();

   label.setPicture(pic);
   label.show();
   return a.exec();
}