Qt 官方demo Basic Drawing 詳解

前言:

來看一個 qt 自己的demo ，然後細細的看下他們的代碼能學到一些新知識
比如 tr("&S") 加這個& 代表什麼意思
setBuddy() 函數的作用等等

入口:

效果圖:

#####1. 先看下整個的項目結構:

兩個類
renderarea
window
2個資源圖片

還是很簡單的一個小demo

2.看main 函數

很簡單上來先初始化資源

然後實例化 window 類

window 類結構

window.h

#ifndef WINDOW_H
#define WINDOW_H

#include <QWidget>

QT_BEGIN_NAMESPACE
class QCheckBox;
class QComboBox;
class QLabel;
class QSpinBox;
QT_END_NAMESPACE
class RenderArea;

//! [0]
class Window : public QWidget
{
    Q_OBJECT

public:
    Window();

private slots:
    void shapeChanged();
    void penChanged();
    void brushChanged();

private:
    RenderArea *renderArea;
    QLabel *shapeLabel;
    QLabel *penWidthLabel;
    QLabel *penStyleLabel;
    QLabel *penCapLabel;
    QLabel *penJoinLabel;
    QLabel *brushStyleLabel;
    QLabel *otherOptionsLabel;
    QComboBox *shapeComboBox;
    QSpinBox *penWidthSpinBox;
    QComboBox *penStyleComboBox;
    QComboBox *penCapComboBox;
    QComboBox *penJoinComboBox;
    QComboBox *brushStyleComboBox;
    QCheckBox *antialiasingCheckBox;
    QCheckBox *transformationsCheckBox;
};
//! [0]

#endif // WINDOW_H

window.cpp

#include "renderarea.h"
#include "window.h"

#include <QtWidgets>

//! [0]
const int IdRole = Qt::UserRole;
//! [0]

//! [1]
Window::Window()
{
    renderArea = new RenderArea;

    shapeComboBox = new QComboBox;
    shapeComboBox->addItem(tr("Polygon"), RenderArea::Polygon);
    shapeComboBox->addItem(tr("Rectangle"), RenderArea::Rect);
    shapeComboBox->addItem(tr("Rounded Rectangle"), RenderArea::RoundedRect);
    shapeComboBox->addItem(tr("Ellipse"), RenderArea::Ellipse);
    shapeComboBox->addItem(tr("Pie"), RenderArea::Pie);
    shapeComboBox->addItem(tr("Chord"), RenderArea::Chord);
    shapeComboBox->addItem(tr("Path"), RenderArea::Path);
    shapeComboBox->addItem(tr("Line"), RenderArea::Line);
    shapeComboBox->addItem(tr("Polyline"), RenderArea::Polyline);
    shapeComboBox->addItem(tr("Arc"), RenderArea::Arc);
    shapeComboBox->addItem(tr("Points"), RenderArea::Points);
    shapeComboBox->addItem(tr("Text"), RenderArea::Text);
    shapeComboBox->addItem(tr("Pixmap"), RenderArea::Pixmap);

    shapeLabel = new QLabel(tr("&Shape:"));
    shapeLabel->setBuddy(shapeComboBox);
//! [1]

//! [2]
    penWidthSpinBox = new QSpinBox;
    penWidthSpinBox->setRange(0, 20);
    penWidthSpinBox->setSpecialValueText(tr("0 (cosmetic pen)"));

    penWidthLabel = new QLabel(tr("&Pen Width:"));
    penWidthLabel->setBuddy(penWidthSpinBox);
//! [2]

//! [3]
    penStyleComboBox = new QComboBox;
    penStyleComboBox->addItem(tr("Solid"), static_cast<int>(Qt::SolidLine));
    penStyleComboBox->addItem(tr("Dash"), static_cast<int>(Qt::DashLine));
    penStyleComboBox->addItem(tr("Dot"), static_cast<int>(Qt::DotLine));
    penStyleComboBox->addItem(tr("Dash Dot"), static_cast<int>(Qt::DashDotLine));
    penStyleComboBox->addItem(tr("Dash Dot Dot"), static_cast<int>(Qt::DashDotDotLine));
    penStyleComboBox->addItem(tr("None"), static_cast<int>(Qt::NoPen));

    penStyleLabel = new QLabel(tr("&Pen Style:"));
    penStyleLabel->setBuddy(penStyleComboBox);

    penCapComboBox = new QComboBox;
    penCapComboBox->addItem(tr("Flat"), Qt::FlatCap);
    penCapComboBox->addItem(tr("Square"), Qt::SquareCap);
    penCapComboBox->addItem(tr("Round"), Qt::RoundCap);

    penCapLabel = new QLabel(tr("Pen &Cap:"));
    penCapLabel->setBuddy(penCapComboBox);

    penJoinComboBox = new QComboBox;
    penJoinComboBox->addItem(tr("Miter"), Qt::MiterJoin);
    penJoinComboBox->addItem(tr("Bevel"), Qt::BevelJoin);
    penJoinComboBox->addItem(tr("Round"), Qt::RoundJoin);

    penJoinLabel = new QLabel(tr("Pen &Join:"));
    penJoinLabel->setBuddy(penJoinComboBox);
//! [3]

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

    brushStyleLabel = new QLabel(tr("&Brush:"));
    brushStyleLabel->setBuddy(brushStyleComboBox);
//! [4]

//! [5]
    otherOptionsLabel = new QLabel(tr("Options:"));
//! [5] //! [6]
    antialiasingCheckBox = new QCheckBox(tr("&Antialiasing"));
//! [6] //! [7]
    transformationsCheckBox = new QCheckBox(tr("&Transformations"));
//! [7]

//! [8]
    connect(shapeComboBox, SIGNAL(activated(int)),
            this, SLOT(shapeChanged()));
    connect(penWidthSpinBox, SIGNAL(valueChanged(int)),
            this, SLOT(penChanged()));
    connect(penStyleComboBox, SIGNAL(activated(int)),
            this, SLOT(penChanged()));
    connect(penCapComboBox, SIGNAL(activated(int)),
            this, SLOT(penChanged()));
    connect(penJoinComboBox, SIGNAL(activated(int)),
            this, SLOT(penChanged()));
    connect(brushStyleComboBox, SIGNAL(activated(int)),
            this, SLOT(brushChanged()));
    connect(antialiasingCheckBox, SIGNAL(toggled(bool)),
            renderArea, SLOT(setAntialiased(bool)));
    connect(transformationsCheckBox, SIGNAL(toggled(bool)),
            renderArea, SLOT(setTransformed(bool)));
//! [8]

//! [9]
    QGridLayout *mainLayout = new QGridLayout;
//! [9] //! [10]
    mainLayout->setColumnStretch(0, 1);
    mainLayout->setColumnStretch(3, 1);
    mainLayout->addWidget(renderArea, 0, 0, 1, 4);
    mainLayout->addWidget(shapeLabel, 2, 0, Qt::AlignRight);
    mainLayout->addWidget(shapeComboBox, 2, 1);
    mainLayout->addWidget(penWidthLabel, 3, 0, Qt::AlignRight);
    mainLayout->addWidget(penWidthSpinBox, 3, 1);
    mainLayout->addWidget(penStyleLabel, 4, 0, Qt::AlignRight);
    mainLayout->addWidget(penStyleComboBox, 4, 1);
    mainLayout->addWidget(penCapLabel, 3, 2, Qt::AlignRight);
    mainLayout->addWidget(penCapComboBox, 3, 3);
    mainLayout->addWidget(penJoinLabel, 2, 2, Qt::AlignRight);
    mainLayout->addWidget(penJoinComboBox, 2, 3);
    mainLayout->addWidget(brushStyleLabel, 4, 2, Qt::AlignRight);
    mainLayout->addWidget(brushStyleComboBox, 4, 3);
    mainLayout->addWidget(otherOptionsLabel, 5, 0, Qt::AlignRight);
    mainLayout->addWidget(antialiasingCheckBox, 5, 1, 1, 1, Qt::AlignRight);
    mainLayout->addWidget(transformationsCheckBox, 5, 2, 1, 2, Qt::AlignRight);
    setLayout(mainLayout);

    shapeChanged();
    penChanged();
    brushChanged();
    antialiasingCheckBox->setChecked(true);

    setWindowTitle(tr("Basic Drawing"));
}
//! [10]

//! [11]
void Window::shapeChanged()
{
    RenderArea::Shape shape = RenderArea::Shape(shapeComboBox->itemData(
            shapeComboBox->currentIndex(), IdRole).toInt());
    renderArea->setShape(shape);
}
//! [11]

//! [12]
void Window::penChanged()
{
    int width = penWidthSpinBox->value();
    Qt::PenStyle style = Qt::PenStyle(penStyleComboBox->itemData(
            penStyleComboBox->currentIndex(), IdRole).toInt());
    Qt::PenCapStyle cap = Qt::PenCapStyle(penCapComboBox->itemData(
            penCapComboBox->currentIndex(), IdRole).toInt());
    Qt::PenJoinStyle join = Qt::PenJoinStyle(penJoinComboBox->itemData(
            penJoinComboBox->currentIndex(), IdRole).toInt());

    renderArea->setPen(QPen(Qt::blue, width, style, cap, join));
}
//! [12]

//! [13]
void Window::brushChanged()
{
    Qt::BrushStyle style = Qt::BrushStyle(brushStyleComboBox->itemData(
//! [13]
            brushStyleComboBox->currentIndex(), IdRole).toInt());

//! [14]
    if (style == Qt::LinearGradientPattern) {
        QLinearGradient linearGradient(0, 0, 100, 100);
        linearGradient.setColorAt(0.0, Qt::white);
        linearGradient.setColorAt(0.2, Qt::green);
        linearGradient.setColorAt(1.0, Qt::black);
        renderArea->setBrush(linearGradient);
//! [14] //! [15]
    } else if (style == Qt::RadialGradientPattern) {
        QRadialGradient radialGradient(50, 50, 50, 70, 70);
        radialGradient.setColorAt(0.0, Qt::white);
        radialGradient.setColorAt(0.2, Qt::green);
        radialGradient.setColorAt(1.0, Qt::black);
        renderArea->setBrush(radialGradient);
    } else if (style == Qt::ConicalGradientPattern) {
        QConicalGradient conicalGradient(50, 50, 150);
        conicalGradient.setColorAt(0.0, Qt::white);
        conicalGradient.setColorAt(0.2, Qt::green);
        conicalGradient.setColorAt(1.0, Qt::black);
        renderArea->setBrush(conicalGradient);
//! [15] //! [16]
    } else if (style == Qt::TexturePattern) {
        renderArea->setBrush(QBrush(QPixmap(":/images/brick.png")));
//! [16] //! [17]
    } else {
        renderArea->setBrush(QBrush(Qt::green, style));
    }
}
//! [17]

他的界面是代碼寫的然後都是一些基本的控件除了類RenderArea 這個暫時不管先看構造函數

window 構造函數

shape 的combox additem 用的重載的可以寫QVariant 類型的這裏是枚舉

    shapeLabel = new QLabel(tr("&Shape:"));
  shapeLabel->setBuddy(shapeComboBox);

tr("&") 和 setBuddy（）幹啥的？

我也沒見過啊我去查了一下這倆是配合使用的

shapeLabel 的快捷鍵是 “ALT+w”，按下快捷鍵時，輸入焦點自動跳到label的buddy shapeComboBox上。
個人理解：這段代碼shapeLabel->setBuddy(shapeComboBox);是設置行編輯器作爲label 的夥伴，所謂夥伴（buddy）就是就是一個窗口部件，按上面英文就是當你按下快捷鍵的時候，這個快捷鍵是在label上標明的，然後焦點就會移動到label的小夥伴身上

QLabel(tr("&Shape:")); 就不是 ALT + W 了是ALT + &後面的第一個字母
也就是 ALT + S 就把焦點跳到 Combox 上面

效果圖:

這裏還是和上面一樣重載的把類型轉爲了 int

是爲了配合下面的信號槽使用

這樣寫起來方便,不需要在根據所選擇的條目不同發送不同的信號

這點也學到了以後

基本上這個類就結束了就是些控件初始化然後佈局了，
咱們開始看下一個繪圖類

Renderarea 類結構

renderarea.h

#ifndef RENDERAREA_H
#define RENDERAREA_H

#include <QBrush>
#include <QPen>
#include <QPixmap>
#include <QWidget>

//! [0]
class RenderArea : public QWidget
{
    Q_OBJECT

public:
    enum Shape { Line, Points, Polyline, Polygon, Rect, RoundedRect, Ellipse, Arc,
                 Chord, Pie, Path, Text, Pixmap };

    RenderArea(QWidget *parent = 0);

    QSize minimumSizeHint() const override;
    QSize sizeHint() const override;

public slots:
    void setShape(Shape shape);
    void setPen(const QPen &pen);
    void setBrush(const QBrush &brush);
    void setAntialiased(bool antialiased);
    void setTransformed(bool transformed);

protected:
    void paintEvent(QPaintEvent *event) override;

private:
    Shape shape;
    QPen pen;
    QBrush brush;
    bool antialiased;
    bool transformed;
    QPixmap pixmap;
};
//! [0]

#endif // RENDERAREA_H

renderarea.cpp

#include "renderarea.h"

#include <QPainter>

//! [0]
RenderArea::RenderArea(QWidget *parent)
    : QWidget(parent)
{
    shape = Polygon;
    antialiased = false;
    transformed = false;
    pixmap.load(":/images/qt-logo.png");

    setBackgroundRole(QPalette::Base);
    setAutoFillBackground(true);
}
//! [0]

//! [1]
QSize RenderArea::minimumSizeHint() const
{
    return QSize(100, 100);
}
//! [1]

//! [2]
QSize RenderArea::sizeHint() const
{
    return QSize(400, 200);
}
//! [2]

//! [3]
void RenderArea::setShape(Shape shape)
{
    this->shape = shape;
    update();
}
//! [3]

//! [4]
void RenderArea::setPen(const QPen &pen)
{
    this->pen = pen;
    update();
}
//! [4]

//! [5]
void RenderArea::setBrush(const QBrush &brush)
{
    this->brush = brush;
    update();
}
//! [5]

//! [6]
void RenderArea::setAntialiased(bool antialiased)
{
    this->antialiased = antialiased;
    update();
}
//! [6]

//! [7]
void RenderArea::setTransformed(bool transformed)
{
    this->transformed = transformed;
    update();
}
//! [7]

//! [8]
void RenderArea::paintEvent(QPaintEvent * /* event */)
{
    static const QPoint points[4] = {
        QPoint(10, 80),
        QPoint(20, 10),
        QPoint(80, 30),
        QPoint(90, 70)
    };

    QRect rect(10, 20, 80, 60);

    QPainterPath path;
    path.moveTo(20, 80);
    path.lineTo(20, 30);
    path.cubicTo(80, 0, 50, 50, 80, 80);

    int startAngle = 20 * 16;
    int arcLength = 120 * 16;
//! [8]

//! [9]
    QPainter painter(this);
    painter.setPen(pen);
    painter.setBrush(brush);
    if (antialiased)
        painter.setRenderHint(QPainter::Antialiasing, true);
//! [9]

//! [10]
    for (int x = 0; x < width(); x += 100) {
        for (int y = 0; y < height(); y += 100) {
            painter.save();
            painter.translate(x, y);
//! [10] //! [11]
            if (transformed) {
                painter.translate(50, 50);
                painter.rotate(60.0);
                painter.scale(0.6, 0.9);
                painter.translate(-50, -50);
            }
//! [11]

//! [12]
            switch (shape) {
            case Line:
                painter.drawLine(rect.bottomLeft(), rect.topRight());
                break;
            case Points:
                painter.drawPoints(points, 4);
                break;
            case Polyline:
                painter.drawPolyline(points, 4);
                break;
            case Polygon:
                painter.drawPolygon(points, 4);
                break;
            case Rect:
                painter.drawRect(rect);
                break;
            case RoundedRect:
                painter.drawRoundedRect(rect, 25, 25, Qt::RelativeSize);
                break;
            case Ellipse:
                painter.drawEllipse(rect);
                break;
            case Arc:
                painter.drawArc(rect, startAngle, arcLength);
                break;
            case Chord:
                painter.drawChord(rect, startAngle, arcLength);
                break;
            case Pie:
                painter.drawPie(rect, startAngle, arcLength);
                break;
            case Path:
                painter.drawPath(path);
                break;
            case Text:
                painter.drawText(rect,
                                 Qt::AlignCenter,
                                 tr("Qt by\nThe Qt Company"));
                break;
            case Pixmap:
                painter.drawPixmap(10, 10, pixmap);
            }
//! [12] //! [13]
            painter.restore();
        }
    }

    painter.setRenderHint(QPainter::Antialiasing, false);
    painter.setPen(palette().dark().color());
    painter.setBrush(Qt::NoBrush);
    painter.drawRect(QRect(0, 0, width() - 1, height() - 1));
}
//! [13]

繼承了 qwidget

寫了一個枚舉代表某些形狀

重載了父類的一些函數

加 override 的好處就是顯示的代表重載然後編譯器會找父類的這個函數如果找不到就報錯
如果不加 override ,如果寫錯了個字母就不是重載了是實現了自己的新函數

這類裏沒有啥咱們只看 PaintEvent

PaintEvent

void RenderArea::paintEvent(QPaintEvent * /* event */)
{
    static const QPoint points[4] = {
        QPoint(10, 80),
        QPoint(20, 10),
        QPoint(80, 30),
        QPoint(90, 70)
    };

    QRect rect(10, 20, 80, 60);

    QPainterPath path;
    path.moveTo(20, 80);
    path.lineTo(20, 30);
    path.cubicTo(80, 0, 50, 50, 80, 80);

    int startAngle = 20 * 16;
    int arcLength = 120 * 16;
//! [8]

//! [9]
    QPainter painter(this);
    painter.setPen(pen);
    painter.setBrush(brush);
    if (antialiased)
        painter.setRenderHint(QPainter::Antialiasing, true);
//! [9]

//! [10]
    for (int x = 0; x < width(); x += 100) {
        for (int y = 0; y < height(); y += 100) {
            painter.save();
            painter.translate(x, y);
//! [10] //! [11]
            if (transformed) {
                painter.translate(50, 50);
                painter.rotate(60.0);
                painter.scale(0.6, 0.9);
                painter.translate(-50, -50);
            }
//! [11]

//! [12]
            switch (shape) {
            case Line:
                painter.drawLine(rect.bottomLeft(), rect.topRight());
                break;
            case Points:
                painter.drawPoints(points, 4);
                break;
            case Polyline:
                painter.drawPolyline(points, 4);
                break;
            case Polygon:
                painter.drawPolygon(points, 4);
                break;
            case Rect:
                painter.drawRect(rect);
                break;
            case RoundedRect:
                painter.drawRoundedRect(rect, 25, 25, Qt::RelativeSize);
                break;
            case Ellipse:
                painter.drawEllipse(rect);
                break;
            case Arc:
                painter.drawArc(rect, startAngle, arcLength);
                break;
            case Chord:
                painter.drawChord(rect, startAngle, arcLength);
                break;
            case Pie:
                painter.drawPie(rect, startAngle, arcLength);
                break;
            case Path:
                painter.drawPath(path);
                break;
            case Text:
                painter.drawText(rect,
                                 Qt::AlignCenter,
                                 tr("Qt by\nThe Qt Company"));
                break;
            case Pixmap:
                painter.drawPixmap(10, 10, pixmap);
            }
//! [12] //! [13]
            painter.restore();
        }
    }

    painter.setRenderHint(QPainter::Antialiasing, false);
    painter.setPen(palette().dark().color());
    painter.setBrush(Qt::NoBrush);
    painter.drawRect(QRect(0, 0, width() - 1, height() - 1));
}

繪製時間會一直調用繪製

這裏函數也沒有啥就是根據 combox 選擇不同枚舉就不同就繪製不同的形狀

結尾:

我們看官方的demo 就是學習他的代碼
代碼,結構整體看下來很清晰明瞭
還學到QCombox additem 重載裏可以寫QVariant 類型
tr("&") 和 setBuddy（）可學到了快捷鍵直接讓某個夥伴得到焦點

Qt 官方demo Basic Drawing 詳解

前言:

入口:

效果圖:

2.看main 函數

window 類結構

window 構造函數

效果圖:

Renderarea 類結構

PaintEvent

結尾:

Qt 圖形視圖框架碰撞檢測官方Demo 移動的小老鼠

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