Qt实用技巧：截屏功能的实现

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需求

        写一个截屏模块。

Demo

        下载地址：​​​

效果截图

核心代码

初始化截屏窗口代码

// 设置无边框
    setWindowFlags(windowFlags() | Qt::FramelessWindowHint);
    // 激活并全屏
    setWindowState(Qt::WindowActive | Qt::WindowFullScreen);
    // 抓取当前屏幕图片，使用QPixmap，Qt5.9.3会有提示信息
    // this function is deprecated, use QScreen::grabWindow() instead.
    // Defaulting to primary screen.
    _pixmapScreen = QPixmap::grabWindow(QApplication::desktop()->winId());
    _screenWidth = _pixmapScreen.width();
    _screenHeight = _pixmapScreen.height();

绘制代码

QPainter painter(this);
    // 背景刷图
    QColor shadowColor = QColor(0, 0, 0, 100);
    painter.drawPixmap(0, 0, _pixmapScreen);
    painter.fillRect(_pixmapScreen.rect(), shadowColor);
    if(_bPressed)
    {
        QRect selectedRect(_pointStart, _pointEnd);
        // QRect允许负值，使用mormalized转化为正值
        selectedRect = selectedRect.normalized();
        // 截图黑框
        painter.setPen(QPen(Qt::black, 2));
        painter.drawRect(selectedRect);
        // 截图的rect，再次填充
        _pixmapCaptrueScreen = _pixmapScreen.copy(selectedRect);
        painter.drawPixmap(selectedRect.topLeft(), _pixmapCaptrueScreen);
    }

鼠标操作代码

void CaptureScreen::mousePressEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        _bPressed = true;
        _pointStart = event->pos();
        _pointEnd = event->pos();
        update();
    }
}

void CaptureScreen::mouseMoveEvent(QMouseEvent *event)
{
    _pointEnd = event->pos();
    update();
}

void CaptureScreen::mouseReleaseEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        _bPressed = false;
        _pointEnd = event->pos();
        update();
        emit capturePixmapFnished(true, _pixmapCaptrueScreen);
        close();
    }else{
        emit capturePixmapFnished(true, _pixmapCaptrueScreen);
        close();
    }
}