Qt中QPainter实现绘制文本功能的示例代码

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

class Widget : public QWidget
{
    Q_OBJECT

protected:
    void paintEvent(QPaintEvent *);

public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget() override;
};
#endif // WIDGET_H

#include "Widget.h"
#include <QPainter>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{

}

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);

    painter.save(); //保存之前的状态（颜色、字体、角度）

    painter.setPen(Qt::black);
    painter.setFont(QFont("Arial", 16));
    painter.rotate(0);
    painter.drawText(30, 40, "Hello");

    painter.setPen(Qt::red);
    painter.setFont(QFont("Comic Sans MS", 20));
    painter.rotate(20);
    painter.drawText(30, 40, "Hello");

    painter.restore(); //恢复保存时的状态
    painter.drawText(130, 140, "hello");

}
Widget::~Widget() = default;

//指定字体
QFontMetrics metrics(font);
//获取指定字体下相应字符串宽度
int w = metrics.width(text);
//获取指定字体的字符高度
int h = metrics.height();

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QTimer>

class Widget : public QWidget
{
    Q_OBJECT

    int m_sizeFactor;
    QTimer m_timer;

protected slots:
    void onTimeout();
protected:
    void paintEvent(QPaintEvent* );
public:
    explicit Widget(QWidget *parent = nullptr);
    ~Widget() override;
};
#endif // WIDGET_H

#include "Widget.h"
#include <QPainter>
#include <QFontMetrics>
#include <QPoint>
#include <QFont>
#include <QRect>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
{
    m_sizeFactor = 0;
    m_timer.setParent(this);

    connect(&m_timer, SIGNAL(timeout()), this, SLOT(onTimeout()));

    //定时器启动后，每 50ms 触发一次 timeout 信号，调用一次 onTimeout ()
    m_timer.start(50);
}

void Widget::onTimeout()
{
    update();
}

void Widget::paintEvent(QPaintEvent* )
{
    QPainter painter;
    const QString text = "Hello";
    QFont font("Comic Sans MS", 5 + (m_sizeFactor++) % 100);
    //用来计算当前字体下文字的实际宽、高
    QFontMetrics metrics(font);
    const int w = metrics.width(text);
    const int h = metrics.height();
    // 计算文字绘制矩形位置：水平居中、竖直居中，矩形宽高等于文字宽高
    QRect rect((width()-w)/2, (height()-w)/2, w, h);
    
    // 指定绘图设备为当前窗口 this，正式开始绘图
    painter.begin(this);
    painter.setPen(Qt::blue);
    painter.setFont(font);
    painter.drawText(rect, Qt::AlignCenter, text);
    painter.end();
}
Widget::~Widget() = default;