在QGraphicsScene中绘制比例尺？

Question

我正在使用Qt构建地图小部件（类似于Google地图），基本上我使用了QGraphicsScene来显示地图图块。

现在，我想像在Google地图中一样向小部件添加一个比例尺。 关于如何实现这一点的任何建议？

Answer 1

看一下这个例子 ：

构造代码库，如下所示：

• 编写一个继承QAbstractScrollArea的后代类的类（例如QGraphicsView，QMdiArea，QPlainTextEdit，QScrollArea，QTextEdit，QColumnView，QHeaderView，QListView，QTableView，QTreeView等）。
• 在您的类的构造函数中，调用setViewportMargins并设置左侧/顶部/右侧/底部区域长度的边距。
• 创建一个QGridLayout并将您的自定义标尺/缩放比例添加到布局中。
• 设置此布局并调用setLayout

例：

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：标尺类

#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;
};