代码如下:
class ArrowItem : public QGraphicsItem
{
public:
const static float LINE_WIDTH;
const static float ARROW_SIZE;
public:
ArrowItem(QGraphicsItem* parent = 0);
~ArrowItem();
void setData(const QPointF& from,const QRectF& rect);
public:
QRectF boundingRect()const;
void paint(QPainter* painter,const QStyleOptionGraphicsItem* style,QWidget* widget);
private:
QPointF computeTo(const QPointF& from,const QRectF& to);
private:
bool mValid;
QPointF mFrom;
QPointF mTo;
QPointF mP1;
QPointF mP2;
QRectF mRect;
};
const float ArrowItem::LINE_WIDTH = 1.5f;
const float ArrowItem::ARROW_SIZE = 8.0f;
ArrowItem::ArrowItem(QGraphicsItem* parent):
QGraphicsItem(parent),
mValid(false)
{
}
ArrowItem::~ArrowItem()
{
}
QPointF ArrowItem::computeTo(const QPointF& from,const QRectF& to)
{
QPointF center(to.center());
QPointF top(center.x(),to.top());
QPointF right(to.right(),center.y());
QPointF bottom(center.x(),to.bottom());
QPointF left(to.left(),center.y());
//left
if(from.x() < to.left())
{
if(from.y() < to.top())
{
QLineF line1(from,top);
QLineF line2(from,left);
return line1.length() > line2.length() ? left : top;
}
else if(from.y() > to.bottom())
{
QLineF line1(from,left);
QLineF line2(from,bottom);
return line1.length() > line2.length() ? bottom : left;
}
return left;
}
//right
if(from.x() > to.right())
{
if(from.y() < to.top())
{
QLineF line1(from,top);
QLineF line2(from,right);
return line1.length() > line2.length() ? right : top;
}
else if(from.y() > to.bottom())
{
QLineF line1(from,bottom);
QLineF line2(from,right);
return line1.length() > line2.length() ? right : bottom;
}
return right;
}
if(from.y() < to.top())
return top;
else if(from.y() > to.bottom())
return bottom;
Q_ASSERT(0);
return QPointF();
}
void ArrowItem::setData(const QPointF& from,const QRectF& rect)
{
mValid = true;
mFrom = from;
mRect = rect;
if(rect.contains(from))
{
mValid = false;
return;
}
mTo = computeTo(mFrom,mRect);
QLineF line(mFrom,mTo);
qreal angle = ::acos(line.dx()/line.length());
if(line.dy() >= 0)
angle = 3.14159*2 - angle;
mP1 = mTo + QPointF(sin(angle-PI/3)*ARROW_SIZE,cos(angle-PI/3)*ARROW_SIZE);
mP2 = mTo + QPointF(sin(angle-PI+PI/3)*ARROW_SIZE,cos(angle-PI+PI/3)*ARROW_SIZE);
}
QRectF ArrowItem::boundingRect()const
{
qreal extra = (LINE_WIDTH + ARROW_SIZE)/2.0;
QRectF rect= QRectF(mFrom,QSizeF(mTo.x()-mFrom.x(),mTo.y()-mFrom.y())).normalized().
adjusted(-extra,-extra,extra,extra);
return rect;
}
void ArrowItem::paint(QPainter* painter,const QStyleOptionGraphicsItem* style,QWidget* widget)
{
if(!mValid)
return;
painter->setRenderHint(QPainter::Antialiasing);
QPen p(QColor::fromRgb(79,136,187));
painter->setBrush(QBrush(p.color()));
p.setWidthF(LINE_WIDTH);
painter->setPen(p);
painter->drawLine(mFrom,mTo);
painter->drawPolygon(QPolygonF()<<mTo<<mP1<<mP2);
}
void ArrowItem::setData(const QPointF& from,const QRectF& rect)
该函数第一个参数为箭头起点，rect为箭头指向的矩形框，该函数会自动计算箭头终点和箭头相关参数
该代码经过测试 - 完全可以使用
参考:http://www.cnblogs.com/liulun/p/3833006.html