QT实现十字线

效果：

 int resolutionWidth = m_resolution.width();
        int resolutionHeight = m_resolution.height();

        QPixmap pixmap(resolutionWidth, resolutionHeight);
        pixmap.fill(Qt::transparent);

        QPainter painter(&pixmap);
        painter.setPen(QPen(Qt::red, 2)); // 设置画笔颜色为红色，宽度为2

        // 绘制垂直线
        painter.drawLine(resolutionWidth / 2, 0, resolutionWidth / 2, resolutionHeight);
        // 绘制水平线
        painter.drawLine(0, resolutionHeight / 2, resolutionWidth, resolutionHeight / 2);

        int centerX = resolutionWidth / 2;
        int centerY = resolutionHeight / 2;


        // 在十字中间添加值
        QString centerText = "Center";
        QRectF centerRect(centerX + 20,  centerY , 40, 20);
        painter.drawText(centerRect, Qt::AlignCenter, centerText);

//        // 绘制量尺

        int rulerLength = m_resolution.width(); // 量尺长度
        int tickSpacing = 10; // 刻度间距


        // 绘制水平中心线上的量尺
        int rulerStartXHorizontal = centerX - rulerLength / 2; // 水平量尺起始位置X坐标
        int rulerStartYHorizontal = centerY; // 水平量尺起始位置Y坐标

        for (int i = 0; i <= rulerLength; i += tickSpacing) {
            int tickHeight = (i % (tickSpacing * 5) == 0) ? 20 : 10; // 长刻度的高度为20，短刻度的高度为10

            painter.drawLine(rulerStartXHorizontal + i , rulerStartYHorizontal , rulerStartXHorizontal + i, rulerStartYHorizontal - tickHeight ); // 绘制刻度线
        }


        // 绘制垂直中心线上的量尺
        int rulerStartXVertical = centerX; // 垂直量尺起始位置X坐标
        int rulerStartYVertical = centerY + rulerLength / 2; // 垂直量尺起始位置Y坐标

        for (int i = 0; i <= rulerLength; i += tickSpacing) {
            int tickWidth = (i % (tickSpacing * 5) == 0) ? 20 : 10; // 长刻度的宽度为20，短刻度的宽度为10

            painter.drawLine(rulerStartXVertical, rulerStartYVertical - i, rulerStartXVertical - tickWidth, rulerStartYVertical - i); // 绘制刻度线
        }



        ui->workWidget->updatePixmap1(pixmap); // 更新 workWidget 上显示的图像