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