利用QPainter绘制各种图形（Shape, Pen 宽带，颜色，风格，Cap，Join，刷子）

利用QPainter绘制各种图形

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Qt的二维图形引擎是基于QPainter类的。QPainter既可以绘制几何形状（点、线、矩形、椭圆、弧形、弦形、饼状图、多边形和贝塞尔曲线），也可以绘制像素映射、图像和文字。此外，QPainter还支持一些高级特性，例如反走样（针对文字和图形边缘）、像素混合、渐变填充和矢量路径等。QPainter也支持线性变换，例如平移、旋转、错切和缩放。

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本例子中利用QPainter类提供的各种draw函数，绘制各种类型的图形，包括对图形的形状、颜色、填充风格等的选择。 
1、创建paintarea.h

#ifndef PAINTAREA_H
#define PAINTAREA_H

#include <QtGui>

class PaintArea : public QWidget
{
    Q_OBJECT

public:
    enum Shape {Line,Rectangle,RoundRect,Ellipse,Polygon,Polyline,Points,Arc,Path,Text,Pixmap};
    PaintArea(QWidget *parent = 0);

    void setShape(Shape);
    void setPen(QPen);
    void setBrush(QBrush);

    void paintEvent(QPaintEvent *);

private:
    Shape shape;
    QBrush brush;
    QPen pen;
};
#endif // PAINTAREA_H

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2、创建paintarea.cpp文件

#include "paintarea.h"

PaintArea::PaintArea(QWidget *parent) : QWidget(parent)
{
    shape = Line;
    QPalette p = palette();
    p.setColor(QPalette::Window,Qt::white);
    setPalette(p);
    setAutoFillBackground(true);

    setMinimumSize(400,400);
}

void PaintArea::setShape(Shape s)
{
    shape = s;
    update();
}

void PaintArea::setPen(QPen p)
{
    pen = p;
    update();
}

void PaintArea::setBrush(QBrush b)
{
    brush = b;
    update();
}

void PaintArea::paintEvent(QPaintEvent *)
{
    QPainter p(this);
    p.setPen(pen);
    p.setBrush(brush);

    QRect rect(50,100,300,200);

    static const QPoint points[4] = {
        QPoint(150,100),
        QPoint(300,150),
        QPoint(350,250),
        QPoint(100,300)
    };

    int startAngle = 30 * 16;
    int spanAngle = 120 * 16;

    QPainterPath path;
    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);

    switch(shape)
    {
        case Line:
            p.drawLine(rect.topLeft(),rect.bottomRight());
            break;
        case Rectangle:
            p.drawRect(rect);
            break;
        case RoundRect:
            p.drawRoundRect(rect);
            break;
        case Ellipse:
            p.drawEllipse(rect);
            break;
        case Polygon:
            p.drawPolygon(points,4);
            break;
        case Polyline:
            p.drawPolyline(points,4);
            break;
        case Points:
            p.drawPoints(points,4);
            break;
        case Arc:
            p.drawArc(rect,startAngle,spanAngle);
            break;
        case Path:
            p.drawPath(path);
            break;
        case Text:
            p.drawText(rect,Qt::AlignCenter,tr("Hello Qt"));
            break;
        case Pixmap:
            p.drawPixmap(150,150,QPixmap(":/images/butterfly.png"));
            break;
        default:
            break;
    }
}

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3、创建mainwidget.h

#ifndef MAINWIDGET_H
#define MAINWIDGET_H

#include <QtGui>
#include "paintarea.h"

class MainWidget : public QWidget
{
    Q_OBJECT

public:
    MainWidget(QWidget *parent = 0);

public slots:
    void slotShape(int);
    void slotPenWidth(int);
    void slotPenColor();
    void slotPenStyle(int);
    void slotPenCap(int);
    void slotPenJoin(int);
    void slotBrush(int);

private:
    PaintArea *area;

    QComboBox *shapeComboBox;
    QSpinBox *widthSpinBox;
    QComboBox *penStyleComboBox;
    QComboBox *penCapComboBox;
    QComboBox *penJoinComboBox;
    QComboBox *brushStyleComboBox;
    QFrame *colorFrame;
};

#endif // MAINWIDGET_H

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4、创建mainwidget.cpp

#include "mainwidget.h"

MainWidget::MainWidget(QWidget *parent) : QWidget(parent)
{
    area = new PaintArea;

    QLabel *label1 = new QLabel(tr("Shape:"));
    QLabel *label2 = new QLabel(tr("Pen Width:"));
    QLabel *label3 = new QLabel(tr("Pen Color:"));
    QLabel *label4 = new QLabel(tr("Pen Style:"));
    QLabel *label5 = new QLabel(tr("Pen Cap:"));
    QLabel *label6 = new QLabel(tr("Pen Join:"));
    QLabel *label7 = new QLabel(tr("Brush:"));

    shapeComboBox = new QComboBox;
    shapeComboBox->addItem(tr("Line"), PaintArea::Line);
    shapeComboBox->addItem(tr("Polygon"), PaintArea::Polygon);
    shapeComboBox->addItem(tr("Rectangle"), PaintArea::Rectangle);
    shapeComboBox->addItem(tr("Round Rectangle"), PaintArea::RoundRect);
    shapeComboBox->addItem(tr("Ellipse"), PaintArea::Ellipse);
    shapeComboBox->addItem(tr("Path"), PaintArea::Path);
    shapeComboBox->addItem(tr("Polyline"), PaintArea::Polyline);
    shapeComboBox->addItem(tr("Arc"), PaintArea::Arc);
    shapeComboBox->addItem(tr("Points"), PaintArea::Points);
    shapeComboBox->addItem(tr("Text"), PaintArea::Text);
    shapeComboBox->addItem(tr("Pixmap"), PaintArea::Pixmap);
    connect(shapeComboBox,SIGNAL(activated(int)),this,SLOT(slotShape(int)));

    widthSpinBox = new QSpinBox;
    widthSpinBox->setRange(0,20);
    connect(widthSpinBox,SIGNAL(valueChanged(int)),this,SLOT(slotPenWidth(int)));

    colorFrame = new QFrame;
    colorFrame->setAutoFillBackground(true);
    colorFrame->setPalette(QPalette(Qt::blue));
    QPushButton *colorPushButton = new QPushButton(tr("change"));
    connect(colorPushButton,SIGNAL(clicked()),this,SLOT(slotPenColor()));

    penStyleComboBox = new QComboBox;
    penStyleComboBox->addItem(tr("Solid"), Qt::SolidLine);
    penStyleComboBox->addItem(tr("Dash"), Qt::DashLine);
    penStyleComboBox->addItem(tr("Dot"), Qt::DotLine);
    penStyleComboBox->addItem(tr("Dash Dot"), Qt::DashDotLine);
    penStyleComboBox->addItem(tr("Dash Dot Dot"), Qt::DashDotDotLine);
    penStyleComboBox->addItem(tr("None"), Qt::NoPen);
    connect(penStyleComboBox,SIGNAL(activated(int)),this,SLOT(slotPenStyle(int)));

    penCapComboBox = new QComboBox;
    penCapComboBox->addItem(tr("Flat"), Qt::FlatCap);
    penCapComboBox->addItem(tr("Square"), Qt::SquareCap);
    penCapComboBox->addItem(tr("Round"), Qt::RoundCap);
    connect(penCapComboBox,SIGNAL(activated(int)),this,SLOT(slotPenCap(int)));

    penJoinComboBox = new QComboBox;
    penJoinComboBox->addItem(tr("Miter"), Qt::MiterJoin);
    penJoinComboBox->addItem(tr("Bevel"), Qt::BevelJoin);
    penJoinComboBox->addItem(tr("Round"), Qt::RoundJoin);
    connect(penJoinComboBox,SIGNAL(activated(int)),this,SLOT(slotPenJoin(int)));

    brushStyleComboBox = new QComboBox;
    brushStyleComboBox->addItem(tr("Linear Gradient"),
             Qt::LinearGradientPattern);
    brushStyleComboBox->addItem(tr("Radial Gradient"),
             Qt::RadialGradientPattern);
    brushStyleComboBox->addItem(tr("Conical Gradient"),
             Qt::ConicalGradientPattern);
    brushStyleComboBox->addItem(tr("Texture"), Qt::TexturePattern);
    brushStyleComboBox->addItem(tr("Solid"), Qt::SolidPattern);
    brushStyleComboBox->addItem(tr("Horizontal"), Qt::HorPattern);
    brushStyleComboBox->addItem(tr("Vertical"), Qt::VerPattern);
    brushStyleComboBox->addItem(tr("Cross"), Qt::CrossPattern);
    brushStyleComboBox->addItem(tr("Backward Diagonal"), Qt::BDiagPattern);
    brushStyleComboBox->addItem(tr("Forward Diagonal"), Qt::FDiagPattern);
    brushStyleComboBox->addItem(tr("Diagonal Cross"), Qt::DiagCrossPattern);
    brushStyleComboBox->addItem(tr("Dense 1"), Qt::Dense1Pattern);
    brushStyleComboBox->addItem(tr("Dense 2"), Qt::Dense2Pattern);
    brushStyleComboBox->addItem(tr("Dense 3"), Qt::Dense3Pattern);
    brushStyleComboBox->addItem(tr("Dense 4"), Qt::Dense4Pattern);
    brushStyleComboBox->addItem(tr("Dense 5"), Qt::Dense5Pattern);
    brushStyleComboBox->addItem(tr("Dense 6"), Qt::Dense6Pattern);
    brushStyleComboBox->addItem(tr("Dense 7"), Qt::Dense7Pattern);
    brushStyleComboBox->addItem(tr("None"), Qt::NoBrush);
    connect(brushStyleComboBox,SIGNAL(activated(int)),this,SLOT(slotBrush(int)));

    QGridLayout *ctrlLayout = new QGridLayout;
    int labelCol = 0;
    int contentCol = 1;
    ctrlLayout->addWidget(label1,0,labelCol);
    ctrlLayout->addWidget(shapeComboBox,0,contentCol);
    ctrlLayout->addWidget(label2,1,labelCol);
    ctrlLayout->addWidget(widthSpinBox,1,contentCol);
    ctrlLayout->addWidget(label3,2,labelCol);
    ctrlLayout->addWidget(colorFrame,2,contentCol);
    ctrlLayout->addWidget(colorPushButton,2,2);
    ctrlLayout->addWidget(label4,3,labelCol);
    ctrlLayout->addWidget(penStyleComboBox,3,contentCol);
    ctrlLayout->addWidget(label5,4,labelCol);
    ctrlLayout->addWidget(penCapComboBox,4,contentCol);
    ctrlLayout->addWidget(label6,5,labelCol);
    ctrlLayout->addWidget(penJoinComboBox,5,contentCol);
    ctrlLayout->addWidget(label7,6,labelCol);
    ctrlLayout->addWidget(brushStyleComboBox,6,contentCol);

    QHBoxLayout *mainLayout = new QHBoxLayout;
    mainLayout->addWidget(area);
    mainLayout->addLayout(ctrlLayout);
    mainLayout->setMargin(10);
    mainLayout->setSpacing(10);

    setLayout(mainLayout);

    slotShape(0);
    slotPenWidth(0);
    slotPenStyle(0);
    slotPenCap(0);
    slotPenJoin(0);
    slotBrush(0);
}


void MainWidget::slotShape(int value)
{
    PaintArea::Shape shape = PaintArea::Shape(shapeComboBox->itemData(value,Qt::UserRole).toInt());
    area->setShape(shape);
}

void MainWidget::slotPenWidth(int value)
{
    QColor color = colorFrame->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());

     area->setPen(QPen(color, value, style, cap, join));
}

void MainWidget::slotPenColor()
{
    QColor color = QColorDialog::getColor(Qt::blue);

    colorFrame->setPalette(QPalette(color));

    int width = widthSpinBox->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());

    area->setPen(QPen(color, width, style, cap, join));
}

void MainWidget::slotPenStyle(int value)
{
    int width = widthSpinBox->value();
    QColor color = colorFrame->palette().color(QPalette::Window);
    Qt::PenStyle style = Qt::PenStyle(penStyleComboBox->itemData(value,  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());

    area->setPen(QPen(color, width, style, cap, join));
}

void MainWidget::slotPenCap(int value)
{
    int width = widthSpinBox->value();
    QColor color = colorFrame->palette().color(QPalette::Window);
    Qt::PenStyle style = Qt::PenStyle(penStyleComboBox->itemData(
             penStyleComboBox->currentIndex(),  Qt::UserRole).toInt());
    Qt::PenCapStyle cap = Qt::PenCapStyle(penCapComboBox->itemData(value,  Qt::UserRole).toInt());
    Qt::PenJoinStyle join = Qt::PenJoinStyle(penJoinComboBox->itemData(
             penJoinComboBox->currentIndex(),  Qt::UserRole).toInt());

    area->setPen(QPen(color, width, style, cap, join));
}


void MainWidget::slotPenJoin(int value)
{
    int width = widthSpinBox->value();
    QColor color = colorFrame->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(value,  Qt::UserRole).toInt());

    area->setPen(QPen(color, width, style, cap, join));
}

void MainWidget::slotBrush(int value)
{
     Qt::BrushStyle style = Qt::BrushStyle(brushStyleComboBox->itemData(value, Qt::UserRole).toInt());

     if (style == Qt::LinearGradientPattern) {
         QLinearGradient linearGradient(0, 0, 400, 400);
         linearGradient.setColorAt(0.0, Qt::white);
         linearGradient.setColorAt(0.2, Qt::green);
         linearGradient.setColorAt(1.0, Qt::black);
         area->setBrush(linearGradient);
     } else if (style == Qt::RadialGradientPattern) {
         QRadialGradient radialGradient(200, 200, 150, 150, 100);
         radialGradient.setColorAt(0.0, Qt::white);
         radialGradient.setColorAt(0.2, Qt::green);
         radialGradient.setColorAt(1.0, Qt::black);
         area->setBrush(radialGradient);
     } else if (style == Qt::ConicalGradientPattern) {
         QConicalGradient conicalGradient(200, 200, 30);
         conicalGradient.setColorAt(0.0, Qt::white);
         conicalGradient.setColorAt(0.2, Qt::green);
         conicalGradient.setColorAt(1.0, Qt::black);
         area->setBrush(conicalGradient);
     } else if (style == Qt::TexturePattern) {
         area->setBrush(QBrush(QPixmap(":/images/cheese.jpg")));
     } else {
         area->setBrush(QBrush(Qt::green, style));
     }
}

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5、创建资源文件paintbasic.qrc 
6、创建main.cpp

#include <QApplication>
#include "mainwidget.h"

int main(int argc, char * argv[])
{
    QApplication app(argc,argv);

    MainWidget w;
    w.show();

    return app.exec();
}

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6、编译运行 

7、资源代码文件

https://blog.csdn.net/onlyshi/article/details/47953849