程序运行截图如下：
原理：使用QPainter一个部分，一个部分的画
源码：
mygraphicsitem.h
1 ifndef MYGRAPHICSITEM_H 2 #define MYGRAPHICSITEM_H
3
4 #include <QGraphicsItem>
5
6 class MyGraphicsItem:public QGraphicsItem 7 { 8 public: 9 MyGraphicsItem(QGraphicsItem *parent=0); 10 ~MyGraphicsItem(); 11
12 protected: 13 QRectF boundingRect()const; 14 void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget); 15 }; 16
17 #endif // MYGRAPHICSITEM_H
widget.h
1 #ifndef WIDGET_H 2 #define WIDGET_H
3
4 #include <QWidget>
5 class QGraphicsScene; 6
7 namespace Ui { 8 class Widget; 9 } 10
11 class Widget : public QWidget 12 { 13 Q_OBJECT 14
15 public: 16 explicit Widget(QWidget *parent = 0); 17 ~Widget(); 18
19 private: 20 Ui::Widget *ui; 21 QGraphicsScene *m_scene; 22 }; 23
24 #endif // WIDGET_H
main.cpp
1 #include "widget.h"
2 #include <QApplication>
3
4 int main(int argc, char *argv[]) 5 { 6 QApplication a(argc, argv); 7 Widget w; 8 w.show(); 9
10 return a.exec(); 11 }
mygraphicsitem.cpp
1 #include "mygraphicsitem.h"
2 #include <QPainter>
3 #include <QPen>
4 #include <QRectF>
5
6 MyGraphicsItem::MyGraphicsItem(QGraphicsItem *parent): 7 QGraphicsItem(parent) 8 { 9 setFlags(QGraphicsItem::ItemIsSelectable|QGraphicsItem::ItemIsMovable); 10 } 11
12 MyGraphicsItem::~MyGraphicsItem() 13 { 14
15 } 16
17 QRectF MyGraphicsItem::boundingRect() const
18 { 19 return QRectF(-14,-50,55,70); 20 } 21
22 void MyGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) 23 { 24 Q_UNUSED(option) 25 Q_UNUSED(widget) 26 painter->setPen(QPen(Qt::white,1)); 27 painter->drawRect(-14,-50,55,70); 28 painter->setPen(QPen(Qt::red,2)); 29 painter->drawLine(0,0,0,10); 30 painter->drawLine(0,10,30,10); 31 painter->drawLine(30,10,30,0); 32 painter->drawLine(15,10,15,-20); 33 painter->drawLine(15,-20,0,-20); 34 QRectF rectangle(0,-33,30,30); 35 int startAngle=-180*16; 36 int spanAngle=270*16; 37 painter->drawArc(rectangle, startAngle, spanAngle); 38 painter->drawLine(15,-35,15,-40); 39 }
widget.cpp
1 #include "widget.h"
2 #include "ui_widget.h"
3 #include "mygraphicsitem.h"
4 #include <QGraphicsScene>
5
6 Widget::Widget(QWidget *parent) : 7 QWidget(parent), 8 ui(new Ui::Widget) 9 { 10 ui->setupUi(this); 11 m_scene=new QGraphicsScene; 12 ui->graphicsView->setScene(m_scene); 13 ui->graphicsView->setRenderHint(QPainter::Antialiasing); 14 m_scene->setBackgroundBrush(QBrush(Qt::black)); 15 MyGraphicsItem *item=new MyGraphicsItem; 16 item->setPos(0,0); 17 m_scene->addItem(item); 18 } 19
20 Widget::~Widget() 21 { 22 delete ui; 23 }