Drawing Text in Qt

Problem
When you will draw text using QPainter’s drawText method, it will make you very slow (Qt experts say that this is due to high computation of glyph of font).

Workaround

1. Construct a QPainterPath object
2. Add your text by calling addText method of QPainterPath
3. draw text using QPainter’s drawPath method

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How to insert Ruler / Scale type widget into a QAbstractScrollArea type widget?

How to…?
Please structure your code base as following…

1. Write a class inheriting descendants class of QAbstractScrollArea (As example QGraphicsView, QMdiArea, QPlainTextEdit, QScrollArea, QTextEdit, QColumnView, QHeaderView, QListView, QTableView, QTreeView etc.)
2. In the constructor of your class call setViewportMargins and set the margins of left/top/right/bottom areas length.
3. Create a QGridLayout and adds your custom Ruler/Scale in the layout.
4. Set this layout calling setLayout

Example…
Once I needed to create horizontal/vertical ruler/scale in a QGraphicsView. I used this technique to do that…

setViewportMargins(RULER_BREADTH,RULER_BREADTH,0,0);
QGridLayout* gridLayout = new QGridLayout();
gridLayout->setSpacing(0);
gridLayout->setMargin(0);

mHorzRuler = new QDRuler(QDRuler::Horizontal);
mVertRuler = new QDRuler(QDRuler::Vertical);

QWidget* fake = new QWidget();
fake->setBackgroundRole(QPalette::Window);
fake->setFixedSize(RULER_BREADTH,RULER_BREADTH);
gridLayout->addWidget(fake,0,0);
gridLayout->addWidget(mHorzRuler,0,1);
gridLayout->addWidget(mVertRuler,1,0);
gridLayout->addWidget(this->viewport(),1,1);

this->setLayout(gridLayout);

QDRuler: The ruler class

#define RULER_BREADTH 20

class QDRuler : public QWidget
{
Q_OBJECT
Q_ENUMS(RulerType)
Q_PROPERTY(qreal origin READ origin WRITE setOrigin)
Q_PROPERTY(qreal rulerUnit READ rulerUnit WRITE setRulerUnit)
Q_PROPERTY(qreal rulerZoom READ rulerZoom WRITE setRulerZoom)
public:
  enum RulerType { Horizontal, Vertical };
QDRuler(QDRuler::RulerType rulerType, QWidget* parent) 
: QWidget(parent), mRulerType(rulerType), mOrigin(0.), mRulerUnit(1.),
  mRulerZoom(1.), mMouseTracking(false), mDrawText(false)
{
  setMouseTracking(true);
	QFont txtFont("Goudy Old Style", 5,20);
	txtFont.setStyleHint(QFont::TypeWriter,QFont::PreferOutline);
	setFont(txtFont);
}

QSize minimumSizeHint() const
{
  return QSize(RULER_BREADTH,RULER_BREADTH);
}

QDRuler::RulerType rulerType() const
{
  return mRulerType;
}

qreal origin() const
{
  return mOrigin;
}

qreal rulerUnit() const
{
  return mRulerUnit;
}

qreal rulerZoom() const
{
  return mRulerZoom;
}

public slots:

void setOrigin(const qreal origin)
{
  if (mOrigin != origin)
  {
    mOrigin = origin;
    update();
  }
}

void setRulerUnit(const qreal rulerUnit)
{
  if (mRulerUnit != rulerUnit)
  {
    mRulerUnit = rulerUnit;
    update();
  }
}

void setRulerZoom(const qreal rulerZoom)
{
  if (mRulerZoom != rulerZoom)
  {
    mRulerZoom = rulerZoom;
    update();
  }
}


void setCursorPos(const QPoint cursorPos)
{
  mCursorPos = this->mapFromGlobal(cursorPos);
  mCursorPos += QPoint(RULER_BREADTH,RULER_BREADTH);
  update();
}

void setMouseTrack(const bool track)
{
  if (mMouseTracking != track)
  {
    mMouseTracking = track;
    update();
  }
}

protected:
void mouseMoveEvent(QMouseEvent* event)
{  
  mCursorPos = event->pos();
  update();  
  QWidget::mouseMoveEvent(event);  
}

void paintEvent(QPaintEvent* event)
{
  QPainter painter(this);
	painter.setRenderHints(QPainter::TextAntialiasing | QPainter::HighQualityAntialiasing);
	QPen pen(Qt::black,0); // zero width pen is cosmetic pen
	//pen.setCosmetic(true);
	painter.setPen(pen);
  // We want to work with floating point, so we are considering
  // the rect as QRectF
  QRectF rulerRect = this->rect();

  // at first fill the rect
  //painter.fillRect(rulerRect,QColor(220,200,180));
  painter.fillRect(rulerRect,QColor(236,233,216));

  // drawing a scale of 25
  drawAScaleMeter(&painter,rulerRect,25,(Horizontal == mRulerType ? rulerRect.height()
		: rulerRect.width())/2);
  // drawing a scale of 50
  drawAScaleMeter(&painter,rulerRect,50,(Horizontal == mRulerType ? rulerRect.height()
		: rulerRect.width())/4);
  // drawing a scale of 100
  mDrawText = true;
  drawAScaleMeter(&painter,rulerRect,100,0);
  mDrawText = false;

  // drawing the current mouse position indicator
	painter.setOpacity(0.4);
  drawMousePosTick(&painter);
	painter.setOpacity(1.0);

  // drawing no man's land between the ruler & view
  QPointF starPt = Horizontal == mRulerType ? rulerRect.bottomLeft()
      : rulerRect.topRight();
  QPointF endPt = Horizontal == mRulerType ? rulerRect.bottomRight()
      : rulerRect.bottomRight();
  painter.setPen(QPen(Qt::black,2));
  painter.drawLine(starPt,endPt);
}

private:
void drawAScaleMeter(QPainter* painter, QRectF rulerRect, qreal scaleMeter, qreal startPositoin)
{
  // Flagging whether we are horizontal or vertical only to reduce
  // to cheching many times
  bool isHorzRuler = Horizontal == mRulerType;

  scaleMeter  = scaleMeter * mRulerUnit * mRulerZoom;

  // Ruler rectangle starting mark
  qreal rulerStartMark = isHorzRuler ? rulerRect.left() : rulerRect.top();
  // Ruler rectangle ending mark
  qreal rulerEndMark = isHorzRuler ? rulerRect.right() : rulerRect.bottom();

  // Condition A # If origin point is between the start & end mard,
  //we have to draw both from origin to left mark & origin to right mark.
  // Condition B # If origin point is left of the start mark, we have to draw
  // from origin to end mark.
  // Condition C # If origin point is right of the end mark, we have to draw
  // from origin to start mark.
  if (mOrigin >= rulerStartMark && mOrigin <= rulerEndMark)
  {		
    drawFromOriginTo(painter, rulerRect, mOrigin, rulerEndMark, 0, scaleMeter, startPositoin);
    drawFromOriginTo(painter, rulerRect, mOrigin, rulerStartMark, 0, -scaleMeter, startPositoin);
  }
  else if (mOrigin < rulerStartMark)
  {
		int tickNo = int((rulerStartMark - mOrigin) / scaleMeter);
		drawFromOriginTo(painter, rulerRect, mOrigin + scaleMeter * tickNo,
			rulerEndMark, tickNo, scaleMeter, startPositoin);
  }
  else if (mOrigin > rulerEndMark)
  {
		int tickNo = int((mOrigin - rulerEndMark) / scaleMeter);
    drawFromOriginTo(painter, rulerRect, mOrigin - scaleMeter * tickNo, 
			rulerStartMark, tickNo, -scaleMeter, startPositoin);
  }
}

void drawFromOriginTo(QPainter* painter, QRectF rulerRect, qreal startMark, qreal endMark, int startTickNo, qreal step, qreal startPosition)
{
  bool isHorzRuler = Horizontal == mRulerType;
  int iterate = 0;

  for (qreal current = startMark;
      (step < 0 ? current >= endMark : current <= endMark); current += step)
  {
    qreal x1 = isHorzRuler ? current : rulerRect.left() + startPosition;
    qreal y1 = isHorzRuler ? rulerRect.top() + startPosition : current;
    qreal x2 = isHorzRuler ? current : rulerRect.right();
    qreal y2 = isHorzRuler ? rulerRect.bottom() : current;
    painter->drawLine(QLineF(x1,y1,x2,y2));
    if (mDrawText)
    {
      QPainterPath txtPath;
			txtPath.addText(x1 + 1,y1 + (isHorzRuler ? 7 : -2),this->font(),QString::number(qAbs(int(step) * startTickNo++)));
      painter->drawPath(txtPath);
      iterate++;
    }
  }
}

void drawMousePosTick(QPainter* painter)
{
  if (mMouseTracking)
  {
    QPoint starPt = mCursorPos;
    QPoint endPt;
    if (Horizontal == mRulerType)
    {
      starPt.setY(this->rect().top());
      endPt.setX(starPt.x());
      endPt.setY(this->rect().bottom());
    }
    else
    {
      starPt.setX(this->rect().left());
      endPt.setX(this->rect().right());
      endPt.setY(starPt.y());
    }
    painter->drawLine(starPt,endPt);
  }
}
private:
  RulerType mRulerType;
  qreal mOrigin;
  qreal mRulerUnit;
  qreal mRulerZoom;
  QPoint mCursorPos;
  bool mMouseTracking;
  bool mDrawText;
};

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