Qt5开发从入门到精通——第六篇二节（ 图像与图片——基础图形的绘制 ）

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前言

本章首先介绍几种主要位置函数及其之间的区别，以及各种与位置相关函数的使用场合；然后，通过一个简单绘图工具实例，介绍利用 QPainter 和 QPainterPath 两种方法绘制各种基础图形。

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一、基础图形的绘制概述

设计界面，区分各种形状及画笔颜色、画笔线宽、画笔风格、画笔顶帽、画笔连接点、填充模式、铺展效果、画刷颜色、画刷风格设置等。

二、实例效果

图一

三、原码解析

paintarea.h

#ifndef PAINTAREA_H
#define PAINTAREA_H
#include 
#include 
#include
class PaintArea : public QWidget
{
    Q_OBJECT
public:
    enum Shape{Line,Rectangle,RoundRect,Ellipse,Polygon,Polyline,Points,Arc,Path,Text, Pixmap};
    explicit PaintArea(QWidget *parent = nullptr);       
    void setShape(Shape);
    void setPen (QPen) ;
    void setBrush(QBrush);
    void setFillRule (Qt::FillRule) ;
    void paintEvent(QPaintEvent *);
signals:

public slots:

private:
    Shape shape;
    QPen pen;
    QBrush brush;
    Qt::FillRule fillRule;

};

#endif // PAINTAREA_H

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widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include 
#include 
#include "paintarea.h"
#include 
#include 
#include 
#include 
#include 
#include 
#include 


class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget *parent = 0);
    ~Widget();
private:
    PaintArea *paintArea;
    QLabel *shapeLabel;
    QComboBox *shapeComboBox;
    QLabel *penWidthLabel;
    QSpinBox *penWidthSpinBox;
    QLabel *penColorLabel;
    QFrame *penColorFrame;
    QPushButton *penColorBtn;
    QLabel *penStyleLabel;
    QComboBox *penStyleComboBox;
    QLabel *penCapLabel;
    QComboBox *penCapComboBox;
    QLabel *penJoinLabel;
    QComboBox *penJoinComboBox;
    QLabel *fillRuleLabel;
    QComboBox *fillRuleComboBox;
    QLabel *spreadLabel;
    QComboBox *spreadComboBox;
    QGradient::Spread spread;
    QLabel *brushStyleLabel;
    QComboBox *brushStyleComboBox;
    QLabel *brushColorLabel;
    QFrame *brushColorFrame;
    QPushButton *brushColorBtn;
    QGridLayout *rightLayout;



private slots:

    void ShowShape(int);
    void ShowPenWidth(int);
    void ShowPenColor();
    void ShowPenStyle(int);
    void ShowPenCap(int);
    void ShowPenJoin(int);
    void ShowSpreadStyle();
    void ShowFillRule();
    void ShowBrushColor();
    void ShowBrush(int);


};

#endif // WIDGET_H

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main.cpp

#include "widget.h"
#include 

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QFont f("ZYSong18030",12);
    a.setFont(f);
    Widget w;
    w.show();

    return a.exec();
}

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paintarea.cpp

#include "paintarea.h"
#include 
PaintArea::PaintArea(QWidget *parent) : QWidget(parent)
{
    setPalette (QPalette (Qt:: white));
    setAutoFillBackground(true);      //完成对窗体背景色的设置，与下面的代码效果一致：
    setMinimumSize(400,400);
}
void PaintArea::setShape(Shape s)
{
    shape= s;                    //setShape() 函数可以设置形状
    update();
}
void PaintArea::setPen(QPen p)
{                               //setPen() 函数可以设置画笔
    pen= p;
    update();
}
void PaintArea::setBrush(QBrush b)
{
    brush= b;                   //setBrush() 函数可以设置画刷
    update();
}
void PaintArea::setFillRule(Qt::FillRule rule)
{                                                   
    fillRule =rule;            //setFillRule() 函数可以设置填充模式
    update();                 //重画绘制区窗体
}

void PaintArea::paintEvent(QPaintEvent *)
{
    QPainter p(this); //新建一个 QPainter 对象
    p.setPen(pen);   //设置 QPainter 对象的画笔
    p.setBrush(brush); //设置 QPainter 对象的画刷
    QRect rect(50,100,300,200);  // (a)
    static const QPoint points [4]=  //(b)
    {
            QPoint(150,100),
            QPoint(300,150),
            QPoint(350,250),
            QPoint(100,300)
    };
    int startAngle =30*16;            //(c)
    int spanAngle =120*16;
    QPainterPath path; //新建一个 QPainterPath 对象为画路径做准备
    path.addRect(150,150,100,100);
    path.moveTo(100,100);
    path.cubicTo(300,100,200,200,300,300);
    path.cubicTo(100,300,200,200,100,100);
    path.setFillRule (fillRule);

    switch (shape)
    {                      //(d)
    case Line:             //直线
    p.drawLine(rect.topLeft(),rect.bottomRight()) ;break;
    case Rectangle:        //长方形
    p.drawRect(rect);break;
    case RoundRect:         //圆角方形
    p.drawRoundRect(rect);break;
    case Ellipse:           //椭圆形
    p.drawEllipse(rect); break;
    case Polygon:          //多边形
    p.drawPolygon(points,4); break;
    case Polyline:         //多边线
    p.drawPolyline(points,4);break;
    case Points:          //点
    p.drawPoints(points,4);break;
    case Arc:             //弧
    p.drawArc(rect,startAngle,spanAngle);break;
    case Path:           //路径
    p.drawPath(path);break;
    case Text:           //文字
    p.drawText(rect,Qt::AlignCenter,tr("Hello Qt!"));break;
    case Pixmap:        //图片
    p.drawPixmap(150,150,QPixmap("butterfly.png")); break;
    default: break;
    }

}

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其中，
（a）QRect rect(50,100,300,200)：设定一个方形区域，为画长方形、圆角方形、椭圆等做准备。
（b）static const QPoint points [4]= {…}：创建一个QPoint 的数组，包含四个点，为画多边形、多边线及点做准备。
（c）int startAngle =30*16：其中，参数 startAngle 表示起始角，为弧形的起始点与圆心之间连线与水平方向的夹角；参数 spanAngle 表示的是跨度角，为弧形起点、终点分别与圆心连线之间的夹角。
（d） switch (shape){…}：使用 一个 switchO语句，对所要画的形状做判断，调用 QPainter 的各
个 draw()函数完成图形的绘制 。

widget.cpp

#include "widget.h"

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    paintArea =new PaintArea;
    shapeLabel =new QLabel(tr(" 形状："));       //形状选择下拉列表框
    shapeComboBox =new QComboBox;
    shapeComboBox->addItem (tr("Line"),PaintArea:: Line);  //(a)
    shapeComboBox->addItem(tr("Rectangle"),PaintArea::Rectangle);
    shapeComboBox->addItem(tr("RoundedRect"),PaintArea::RoundRect);
    shapeComboBox->addItem(tr("Ellipse"),PaintArea::Ellipse);
    shapeComboBox->addItem(tr("Polygon"),PaintArea::Polygon);
    shapeComboBox->addItem(tr("Polyline"),PaintArea::Polyline);
    shapeComboBox->addItem(tr("Points"),PaintArea::Points);
    shapeComboBox->addItem (tr ("Arc"), PaintArea::Arc);
    shapeComboBox->addItem(tr("Path"),PaintArea::Path);
    shapeComboBox->addItem(tr("Text"),PaintArea::Text);
    shapeComboBox->addItem(tr("Pixmap"),PaintArea::Pixmap);
    connect(shapeComboBox,SIGNAL(activated(int)),this,SLOT(ShowShape(int)));
    penColorLabel =new QLabel(tr(" 画笔颜色："));      //画笔颜色选择控件
    penColorFrame =new QFrame;
    penColorFrame->setFrameStyle(QFrame::Panel|QFrame::Sunken);
    penColorFrame->setAutoFillBackground(true);
    penColorFrame->setPalette(QPalette(Qt::blue));
    penColorBtn =new QPushButton(tr(" 更改"));
    connect(penColorBtn,SIGNAL(clicked()),this,SLOT(ShowPenColor()));
    penWidthLabel =new QLabel(tr(" 画笔线宽："));    //画笔线宽选择控件
    penWidthSpinBox =new QSpinBox;
    penWidthSpinBox->setRange(0,20);
    connect(penWidthSpinBox,SIGNAL(valueChanged(int)),this,SLOT (ShowPenWidth(int)));
    penStyleLabel =new QLabel(tr(" 画笔风格："));   //画笔风格选择下拉表框
    penStyleComboBox =new QComboBox;
    penStyleComboBox->addItem(tr("SolidLine"),static_cast<int>(Qt::SolidLine)); //(b)
    penStyleComboBox->addItem(tr("DashLine"),static_cast<int>(Qt::DashLine));
    penStyleComboBox->addItem(tr("DotLine"),static_cast<int>(Qt::DotLine));
    penStyleComboBox->addItem(tr("DashDotLine"),static_cast<int>(Qt::DashDotLine));
    penStyleComboBox->addItem(tr("DashDotDotLine"),static_cast<int>(Qt::DashDotDotLine));
    penStyleComboBox->addItem(tr("CustomDashLine"),static_cast<int>(Qt::CustomDashLine));
    connect(penStyleComboBox,SIGNAL(activated(int)),this,SLOT (ShowPenStyle(int)));
    penCapLabel =new QLabel(tr(" 画笔顶帽："));   //画笔顶帽风格选择下拉列表框
    penCapComboBox =new QComboBox;
    penCapComboBox->addItem(tr("SquareCap"),Qt::SquareCap);   //(c)
    penCapComboBox->addItem(tr("FlatCap"),Qt::FlatCap);
    penCapComboBox->addItem(tr("RoundCap"),Qt::RoundCap);
    connect(penCapComboBox,SIGNAL(activated(int)),this,SLOT (ShowPenCap (int)));
    penJoinLabel =new QLabel(tr(" 画笔连接点： "));  //画笔连接点风格选择下拉框
    penJoinComboBox =new QComboBox;
    penJoinComboBox->addItem(tr("BevelJoin"),Qt::BevelJoin);  //(d)
    penJoinComboBox->addItem(tr("MiterJoin"),Qt::MiterJoin);
    penJoinComboBox->addItem(tr("RoundJoin"),Qt::RoundJoin);
    connect(penJoinComboBox,SIGNAL(activated(int)),this,SLOT (ShowPenJoin (int)));
    fillRuleLabel =new QLabel( tr ("填充模式："));   //填充模式选择下拉列表框
    fillRuleComboBox =new QComboBox;
    fillRuleComboBox->addItem(tr("Odd Even"),Qt::OddEvenFill);  //(e)
    fillRuleComboBox->addItem(tr("Winding"),Qt::WindingFill);
    connect(fillRuleComboBox,SIGNAL(activated(int)),this,SLOT (ShowFillRule()));
    spreadLabel =new QLabel(tr(" 铺展效果："));  //铺展效果选择下拉列表框
    spreadComboBox =new QComboBox;
    spreadComboBox->addItem(tr("PadSpread"),QGradient::PadSpread);  //(f)
    spreadComboBox->addItem(tr("RepeatSpread"),QGradient::RepeatSpread);
    spreadComboBox->addItem(tr("ReflectSpread"),QGradient:: ReflectSpread);
    connect(spreadComboBox,SIGNAL(activated(int)),this,SLOT(ShowSpreadStyle()));
    brushColorLabel =new QLabel(tr(" 画刷颜色："));  //画刷颜色选择控件
    brushColorFrame =new QFrame;
    brushColorFrame->setFrameStyle(QFrame:: Panel|QFrame:: Sunken) ;
    brushColorFrame->setAutoFillBackground(true);
    brushColorFrame->setPalette(QPalette(Qt::green));
    brushColorBtn =new QPushButton(tr(" 更改")) ;
    connect (brushColorBtn, SIGNAL (clicked()), this, SLOT (ShowBrushColor ()));
    brushStyleLabel =new QLabel(tr(" 画刷风格："));   //画刷风格选择下拉列表框
    brushStyleComboBox =new QComboBox;
    brushStyleComboBox->addItem(tr("SolidPattern"),static_cast<int>(Qt::SolidPattern));   //(g)
    brushStyleComboBox->addItem(tr("DenselPattern"),static_cast<int>(Qt::Dense1Pattern));
    brushStyleComboBox->addItem(tr("Dense2Pattern"),static_cast<int>(Qt::Dense2Pattern));
    brushStyleComboBox->addItem(tr("Dense3Pattern"),static_cast<int>(Qt::Dense3Pattern));
    brushStyleComboBox->addItem(tr("Dense4Pattern"),static_cast<int>(Qt::Dense4Pattern));
    brushStyleComboBox->addItem(tr("Dense5Pattern"),static_cast<int>(Qt::Dense5Pattern));
    brushStyleComboBox->addItem(tr("Dense6Pattern"),static_cast<int>(Qt::Dense6Pattern));
    brushStyleComboBox->addItem(tr("Dense7Pattern"),static_cast<int>(Qt::Dense7Pattern));
    brushStyleComboBox->addItem(tr("HorPattern"),static_cast<int>(Qt::HorPattern));
    brushStyleComboBox->addItem(tr("VerPattern"),static_cast<int>(Qt::VerPattern));
    brushStyleComboBox->addItem(tr("CrossPattern"),static_cast<int>(Qt::CrossPattern));
    brushStyleComboBox->addItem(tr("BDiagPattern"),static_cast<int>(Qt::BDiagPattern));
    brushStyleComboBox->addItem(tr("FDiagPattern"),static_cast<int>(Qt::FDiagPattern));
    brushStyleComboBox->addItem(tr("DiagCrossPattern"),static_cast<int>(Qt:: DiagCrossPattern));
    brushStyleComboBox->addItem(tr("LinearGradientPattern"),static_cast<int>(Qt::LinearGradientPattern));
    brushStyleComboBox->addItem(tr("ConicalGradientPattern"),static_cast<int>(Qt::ConicalGradientPattern));
    brushStyleComboBox->addItem(tr("RadialGradientPattern"),static_cast<int>(Qt::RadialGradientPattern));
    brushStyleComboBox->addItem(tr("TexturePattern"),static_cast<int>(Qt::TexturePattern));
    connect(brushStyleComboBox,SIGNAL(activated(int)),this,SLOT(ShowBrush(int)));
    rightLayout =new QGridLayout;                     //控制面包布局
    rightLayout->addWidget(shapeLabel,0,0);
    rightLayout->addWidget(shapeComboBox,0,1);
    rightLayout->addWidget(penColorLabel,1,0);
    rightLayout->addWidget(penColorFrame,1,1);
    rightLayout->addWidget(penColorBtn,1,2);
    rightLayout->addWidget(penWidthLabel,2,0);
    rightLayout->addWidget(penWidthSpinBox,2,1);
    rightLayout->addWidget(penStyleLabel,3,0);
    rightLayout->addWidget(penStyleComboBox,3,1);
    rightLayout->addWidget(penCapLabel,4,0);
    rightLayout->addWidget(penCapComboBox,4,1);
    rightLayout->addWidget(penJoinLabel,5,0);
    rightLayout->addWidget(penJoinComboBox,5,1);
    rightLayout->addWidget(fillRuleLabel,6,0);
    rightLayout->addWidget(fillRuleComboBox,6,1);
    rightLayout->addWidget(spreadLabel,7,0);
    rightLayout->addWidget(spreadComboBox,7,1);
    rightLayout->addWidget(brushColorLabel,8,0);
    rightLayout->addWidget(brushColorFrame,8,1);
    rightLayout->addWidget(brushColorBtn,8, 2);
    rightLayout->addWidget(brushStyleLabel,9,0);
    rightLayout->addWidget(brushStyleComboBox,9,1);
    QHBoxLayout *mainLayout =new QHBoxLayout(this);        //整体的布局
    mainLayout->addWidget(paintArea);
    mainLayout->addLayout(rightLayout);
    mainLayout->setStretchFactor(paintArea,1);
    mainLayout->setStretchFactor(rightLayout,0);
    ShowShape(shapeComboBox->currentIndex());             //显示默认的图形



}

Widget::~Widget()
{

}

void Widget::ShowShape(int value)
{
    PaintArea::Shape shape= PaintArea::Shape(shapeComboBox->itemData(value, Qt:: UserRole) . toInt());
    paintArea->setShape(shape);
}

void Widget::ShowPenColor()
{
    QColor color= QColorDialog::getColor(static_cast<int>(Qt::blue));
    penColorFrame->setPalette(QPalette(color));
    int value = penWidthSpinBox->value();
    Qt::PenStyle style= Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());
    Qt::PenCapStyle cap= Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());
    Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());
    paintArea->setPen(QPen(color,value,style,cap,join));
}

void Widget::ShowPenWidth(int value)
{
    QColor color= penColorFrame->palette() .color(QPalette::Window);
    Qt::PenStyle style= Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());
    Qt::PenCapStyle cap= Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole) .toInt());
    Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());
    paintArea->setPen(QPen(color,value,style,cap,join));
}

void Widget::ShowPenStyle(int styleValue)
{
    QColor color = penColorFrame->palette().color(QPalette::Window) ;
    int value= penWidthSpinBox->value();
    Qt::PenStyle style= Qt::PenStyle(penStyleComboBox->itemData(styleValue, Qt:: UserRole).toInt ());
    Qt::PenCapStyle cap= Qt::PenCapStyle(penCapComboBox->itemData(penCapComboBox->currentIndex(),Qt::UserRole).toInt());
    Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt()) ;
    paintArea->setPen(QPen(color,value,style,cap,join));

}
void Widget::ShowPenCap(int capValue)
{
    QColor color= penColorFrame->palette() .color(QPalette::Window);
    int value = penWidthSpinBox->value ();
    Qt::PenStyle style= Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex() ,Qt::UserRole).toInt());
    Qt::PenCapStyle cap= Qt::PenCapStyle(penCapComboBox->itemData(capValue, Qt::UserRole).toInt());
    Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(penJoinComboBox->currentIndex(),Qt::UserRole).toInt());
    paintArea->setPen(QPen(color,value,style,cap,join));
}
void Widget::ShowPenJoin(int joinValue)
{
    QColor color = penColorFrame->palette().color(QPalette::Window);
    int value = penWidthSpinBox->value ();
    Qt::PenStyle style= Qt::PenStyle(penStyleComboBox->itemData(penStyleComboBox->currentIndex(),Qt::UserRole).toInt());
    Qt::PenCapStyle cap= Qt::PenCapStyle(penCapComboBox->itemData(
    penCapComboBox->currentIndex(),Qt:: UserRole).toInt());
    Qt::PenJoinStyle join=Qt::PenJoinStyle(penJoinComboBox->itemData(joinValue,Qt::UserRole).toInt());
    paintArea->setPen(QPen(color,value,style,cap,join));
}

void Widget::ShowFillRule()
{
    Qt::FillRule rule=Qt::FillRule(fillRuleComboBox->itemData(fillRuleComboBox->currentIndex (),Qt::UserRole).toInt());
    paintArea->setFillRule(rule);
}
void Widget::ShowSpreadStyle()
{
    spread=QGradient::Spread(spreadComboBox->itemData(spreadComboBox->currentIndex () ,Qt::UserRole).toInt ());
}
void Widget::ShowBrushColor()
{
    QColor color= QColorDialog::getColor(static_cast<int>(Qt:: blue));
    brushColorFrame->setPalette(QPalette(color));
    ShowBrush(brushStyleComboBox->currentIndex());
}
void Widget::ShowBrush(int value)
{
    //获得画刷的颜色
    QColor color= brushColorFrame->palette() .color(QPalette::Window);
    Qt::BrushStyle style= Qt::BrushStyle(brushStyleComboBox->itemData(value, Qt:: UserRole).toInt()); // 获得所选的画刷风格，若选择的是渐变或者纹理图案，则需要进行一定的处理。
    if (style == Qt::LinearGradientPattern)  //主窗口的 style 变量值为 Qt::LinearGradientPattern 时，表明选择的是线形渐变。
    {
        QLinearGradient linearGradient(0,0,400,400);
        linearGradient.setColorAt(0.0,Qt::white);
        linearGradient.setColorAt(0.2,color);
        linearGradient. setColorAt (1.0, Qt::black) ;
        linearGradient.setSpread(spread);
        paintArea->setBrush(linearGradient);
    }else if(style == Qt::RadialGradientPattern)  //主窗口的 style 变量值为 Qt: :RadialGradientPattern 时，表明选择的是圆形渐变。
    {
        QRadialGradient radialGradient(200,200,150,150,100);
        radialGradient.setColorAt(0.0,Qt::white);
        radialGradient.setColorAt(0.2,color) ;
        radialGradient.setColorAt(1.0,Qt::black);
        radialGradient.setSpread(spread);
        paintArea->setBrush(radialGradient);
    }else if (style == Qt::ConicalGradientPattern) //主窗口的 style 变量值为 Qt::ConicalGradientPattern 时，表明选择的是锥形渐变
    {
        QConicalGradient conicalGradient(200,200,30);
        conicalGradient.setColorAt(0.0,Qt::white);
        conicalGradient.setColorAt(0.2,color);
        conicalGradient.setColorAt(1.0,Qt::black);
        paintArea->setBrush(conicalGradient);
    }else if(style == Qt::TexturePattern)
    {
        paintArea->setBrush(QBrush(QPixmap("butterfly.png")));
    }else
    {
        paintArea->setBrush(QBrush(color,style));
    }
}

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其中，
（a）shapeComboBox->addItem (tr(“Line”),PaintArea::Line)：QComboBox 的 addltem()函数
可以仅插入文本，也可同时插入与文本相对应的具体数据，通常为枚举型数据，便千后面操作
时确定选择的是哪个数据。
（b） penStyleComboBox->addItem(tr(“SolidLine”),static_cast(Qt::SolidLine))：选用不同的参数，对应画笔的不同风格。
（c）penCapComboBox->addItem(tr(“SquareCap”),Qt::SquareCap)：选用不同的参数，对应画笔顶帽的不同风格。其中， Qt:: SquareCap 表示在线条的顶点处是方形的，且线条绘制的区域包括了端点，并且再往外延伸半个线宽的长度； Qt: :FlatCap 表示在线条的顶点处是方形的，但线条绘制区域不包括端点在内； Qt: :RoundCap 表示在线条的顶点处是圆形的，且线条绘制区域包含了端点。
（d）penJoinComboBox->addItem(tr(“BevelJoin”),Qt::BevelJoin)：其中， Qt: :BevelJoin 风格连接点是指两条线的中心线顶点相汇，相连处依然保留线条各自的方形顶端； Qt: :MiterJoin 风格连接点是指两条线的中心线顶点相汇，相连处线条延长到线的外侧汇集至点，形成一个尖顶的连接； Qt::RoundJoin 风格连接点是指两条线的中心线顶点相汇，相连处以圆弧形连接。
（e）fillRuleComboBox->addItem(tr(“Odd Even”),Qt::OddEvenFill)：Qt 为 QPainterPath 类提供
了两种填充规则，分别是 Qt: :OddEvenFill 和 Qt::WindingFill。其中， Qt: :OddEvenFill 填充规则判断的依据是从图形中某一点画一条水平线到图形外。若这条水平线与图形边线的交点数目为奇数，则说明此点位千图形的内部；若交点数目为偶数，则此点位于图形的外部而 Qt::WindingFill 填充规则的判断依据则是从图形中某一点画一条水平线到图形外，每个交点外边线的方向可能向上，也可能向下，将这些交点数累加，方向相反的相互抵消，若最后结果不为 0 则说明此点在图形内，若最后结果为 0 则说明在图形外。
（f）spreadComboBox->addItem(tr(“PadSpread”),QGradient::PadSpread)：铺展效果有三
种，分别为 QGradient: :PadSpread 、 QGradient: :RepeatSpread 和 QGradient:: ReflectSpread。其中，PadSpread 是默认的铺展效果，也是最常见的铺展效果，没有被渐变覆盖的区域填充单一的起始
颜色或终止颜色； RepeatSpread 效果与 ReflectSpread 效果只对线性渐变和圆形渐变起作用
（g）brushStyleComboBox->addItem(tr(“SolidPattern”),static_cast(Qt::SolidPattern))：选用不同的参数，对应画刷的不同风格ShowShapeO槽函数，根据当前下拉列表框中选择的选项，调用 PaintArea 类的 setShapeQ 函数设置 PaintArea 对象的形状参数。

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总结

图像与图片的基础图形的绘制会在应用程序开发中经常用到的