【发布时间】：2014-11-13 04:48:41
【问题描述】：
我想在 QGraphicsScene 中实现 arc。我希望在单击三个点时绘制我的弧，以便在单击三个点时绘制弧，其中第一个点将是弧的起点，第二个将是弧上的任何点，第三个将是弧的终点。我曾尝试研究 drawArc 函数，但对 startangle 和 spanangle 感到困惑。我无法动态设置它们。请给我建议一些方法。
我尝试将解决方案嵌入到我的项目中，但出现以下错误：
error: cannot allocate an object of abstract type 'arc'
arcItem = new arc(++id, startP, midP, endP);
你能帮我解决这个问题吗？我正在为我的项目提供部分代码。 在 cadgraphicsscene 的 mousepress 事件中，我做了以下事情。
cadgraphicsscene.cpp
void CadGraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
// mousePressEvent in the graphicsScene
if(mouseEvent->button() == Qt::LeftButton)
{
switch (entityMode)
{
case ArcMode:
if (mFirstClick)
{
startP = mouseEvent->scenePos();
mFirstClick = false;
mSecondClick = true;
}
else if (!mFirstClick && mSecondClick)
{
midP = mouseEvent->scenePos();
mFirstClick = false;
mSecondClick = false;
mThirdClick = true;
}
else if (!mSecondClick && mThirdClick)
{
endP = mouseEvent->scenePos();
mThirdClick = false;
mPaintFlag = true;
}
if (mPaintFlag)
{
arcItem = new arc(++id, startP, midP, endP);
itemList.append(arcItem);
mUndoStack->push(new CadCommandAdd(this, arcItem));
setFlags();
}
}
}
}
arc.cpp
#include "arc.h"
arc::arc(int i, QPointF point1, QPointF point2, QPointF point3)
{
// assigns id
id = i;
p1 = point1;
p2 = point2;
p3 = point3;
lineBC(point2, point3);
lineAC(point1, point3);
lineBA(point2, point1);
rad = qAbs(lineBC.length()/(2*qSin(qDegreesToRadians(lineAC.angleTo(lineBA)))));
bisectorBC(lineBC.pointAt(0.5), lineBC.p2());
bisectorBC.setAngle(lineBC.normalVector().angle());
bisectorBA(lineBA.pointAt(0.5), lineBA.p2());
bisectorBA.setAngle(lineBA.normalVector().angle());
bisectorBA.intersect(bisectorBC, ¢er);
ellipse = new QGraphicsEllipseItem(center.x() - rad, center.y() - rad, rad*2, rad*2);
lineOA(center, point1);
lineOC(center, point3);
}
arc::arc(int i, QLineF start, QLineF end)
{
// assigns id
id = i;
lineOA.angle() = start;
lineOC.angle() - lineOA.angle() = end;
}
int arc::type() const
{
// Enable the use of qgraphicsitem_cast with arc item.
return Type;
}
void arc::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
QWidget *widget)
{
QPen paintpen;
painter->setRenderHint(QPainter::Antialiasing);
paintpen.setWidth(1);
if (isSelected())
{
// sets brush for end points
painter->setBrush(Qt::SolidPattern);
paintpen.setColor(Qt::red);
painter->setPen(paintpen);
paintpen.setStyle(Qt::DashLine);
paintpen.setColor(Qt::black);
painter->setPen(paintpen);
painter->drawArc(ellipse->boundingRect(),lineOA.angle(),lineOC.angle() - lineOA.angle());
}
else
{
painter->setBrush(Qt::SolidPattern);
paintpen.setColor(Qt::black);
painter->setPen(paintpen);
painter->drawArc(ellipse->boundingRect(),lineOA.angle(),lineOC.angle() - lineOA.angle());
}
}
arc.h
include <QGraphicsItem>
#include "qmath.h"
class arc : public QObject, public QGraphicsItem
{
Q_OBJECT
public:
arc(int, QPointF, QPointF, QPointF);
arc(int, QLineF, QLineF);
virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
QWidget *widget);
enum { Type = UserType + 6 };
int type() const;
int id;
QPointF startP, midP, endP, p1, p2, p3,center;
QLineF lineBC;
QLineF lineAC;
QLineF lineBA;
QLineF lineOA;
QLineF lineOC;
QLineF bisectorBC;
QLineF bisectorBA;
QGraphicsEllipseItem *ellipse;
qreal rad;
private:
QVector<QPointF> stuff;
};
#endif // ARC_H
请帮我解决错误。
【问题讨论】：
标签： c++ qt qgraphicsview qgraphicsscene