Qt 文本抗锯齿

1. 通常情况下, 在 paintEvent 中绘制文本时, 不管是否设置抗锯齿选项, 都不会有明显的锯齿, 如下代码所示, Antialiasing/TextAntialiasing 对最终的效果没有显著影响.

    QFont ft = painter.font();
    ft.setFamily("PingFang SC");
    ft.setPixelSize(13);
    ft.setWeight(QFont::Medium);
    painter.setFont(ft);
    painter.setRenderHint(QPainter::Antialiasing, false);
    painter.setRenderHint(QPainter::TextAntialiasing, false);
    // painter.setRenderHint(QPainter::Antialiasing, true);
    // painter.setRenderHint(QPainter::TextAntialiasing, true);
    painter.drawText(0, 0, 200, 50, Qt::AlignCenter, "Test1234567890");

 2. 某些情况下, 我们需要将数据预先绘制到缓存图片上(如多线程构建缓存图片), 再绘制到界面上时, 上述代码就有问题了

    if (image.isNull())
    {
        image = QImage(300, 300, QImage::Format_RGBA8888);
        image.fill(Qt::transparent);
        QPainter painter(&image);
        QFont ft = painter.font();
        ft.setFamily("PingFang SC");
        ft.setPixelSize(13);
        ft.setWeight(QFont::Medium);
        painter.setFont(ft);
        // painter.setRenderHint(QPainter::Antialiasing, false);
        // painter.setRenderHint(QPainter::TextAntialiasing, false);
        painter.setRenderHint(QPainter::Antialiasing, true);
        painter.setRenderHint(QPainter::TextAntialiasing, true);
        painter.drawText(0, 0, 200, 50, Qt::AlignCenter, "Test1234567890");
    }
    painter.drawImage(0, 0, image);

 上述 image 是一个 QImage 对象, 我们启用 Antialiasing/TextAntialiasing, 可以看到文字还是出现了明显的锯齿.

  此时我们需要开启字体的抗锯齿选项, 才能避免出现这种现象:

    if (image.isNull())
    {
        image = QImage(300, 300, QImage::Format_RGBA8888);
        image.fill(Qt::transparent);
        QPainter painter(&image);
        QFont ft = painter.font();
        ft.setFamily("PingFang SC");
        ft.setPixelSize(13);
        ft.setWeight(QFont::Medium);
        ft.setStyleHint(QFont::AnyStyle, QFont::PreferAntialias);
        // ft.setStyleStrategy(QFont::PreferAntialias);
        painter.setFont(ft);
        painter.drawText(0, 0, 200, 50, Qt::AlignCenter, "Test1234567890");
    }
    painter.drawImage(0, 0, image);

通过设置 ft.setStyleHint(QFont::AnyStyle, QFont::PreferAntialias); 或 ft.setStyleStrategy(QFont::PreferAntialias); 之后, 可以看到, 文本锯齿消失了.