自定义Item,点

// cgraphicsitem.h
#ifndef CGRAPHICSITEM_H
#define CGRAPHICSITEM_H

#include <QGraphicsItem>
#include <QGraphicsSceneMouseEvent>
class CGraphicsItem : public QGraphicsItem
{
   
public:
    CGraphicsItem(QPointF p,QGraphicsItem* parent = 0);
    QPointF getPoint(){
   return m_point;}
    void setPoint(QPointF p){
   m_point = p;}
protected:
    virtual QRectF boundingRect() const override;
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override;
    virtual void mouseMoveEvent(QGraphicsSceneMouseEvent *e);
private:
    QPointF m_point;
};

#endif // CGRAPHICSITEM_H

// cgraphicsitem.cpp

#include "cgraphicsitem.h"
#include <QPen>
#include <QBrush>
#include <QPainter>
#include <QGraphicsScene>
#include <QCursor>
CGraphicsItem::CGraphicsItem(QPointF p,QGraphicsItem* parent)
    : m_point(p)
    , QGraphicsItem(parent)
{
   
    setFlags(QGraphicsItem::ItemIsFocusable|
             QGraphicsItem::ItemIsSelectable|
             QGraphicsItem::ItemIsMovable);
    this->setCursor(Qt::PointingHandCursor);
}

QRectF CGraphicsItem::boundingRect() const
{
   
    return QRectF(-4,-4,8,8);
}

void CGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
   
    Q_UNUSED(option);
    Q_UNUSED(widget);
    QPen pen(Qt::yellow,2);
    QBrush brush(Qt::blue);
    this->setPos(m_point);
    painter->setPen(pen);
    painter->setBrush(brush);
    painter->drawEllipse(-4,-4,8,8);
}

void CGraphicsItem::mouseMoveEvent(QGraphicsSceneMouseEvent *e)
{
   
    if(e->buttons() == Qt::LeftButton) {
   
    qreal x = e->scenePos().x() - e->lastScenePos().x();
    qreal y = e->scenePos().y() - e->lastScenePos().y();
    this->parentItem()->moveBy(x,y);
    }
    return QGraphicsItem::mouseMoveEvent(e);
}

scene类负责响应view信号，实时画图

// cgraphicsscene.h
#ifndef CGRAPHICSSCENE_H
#define CGRAPHICSSCENE_H

#include <QGraphicsScene>
#include "cgraphicsitem.h"
#include <QPainterPath>
#include <QGraphicsPathItem>
class CGraphicsScene : public QGraphicsScene
{
   
    Q_OBJECT
public:
    enum Type {
   
        T_None,
        T_Point,
        T_Line,
        T_Circle,
        T_Ellipse,
        T_Rect,
        T_RoundRect,
        T_Polygon,
        T_Bezier
    };
    enum State {
   
        S_None,
        S_Begin,
        S_Moving,
        S_Press,
        S_End
    };

    CGraphicsScene(QObject *parent = 0);
private:
    void BeginDraw(QPointF beginPos,QPointF nextPos,int type);
    void MovingDraw(QPointF beginPos,QPointF movingPos,int type);
    void PressDraw(QPointF beginPos,QPointF pressPos,int type);
    void EndDraw(QPointF beginPos,QPointF endgPos,int type);
public slots:
    void OnDrawImage(QPointF beginPos,QPointF nextPos,int type,int state);
private:
    QList<QGraphicsPathItem*> m_itemList;
    QGraphicsPathItem *m_currentItem;
    QVector<QPointF> m_polygonVec;
    QVector<QPointF> m_bezierVec;
};

#endif // CGRAPHICSSCENE_H

// cgraphicsscene.cpp
#include "cgraphicsscene.h"
#include <cmath>
#include <QPolygonF>