Why is there extra spacing for some characters which cause QPainter::drawText to be cutoff?

I'm trying to use QPainter::drawText() to render some Chinese characters. But in certain fonts, there is extra top spacing when drawing the text. Why is this happening to some characters only?

Tested on Qt version 6.6.3 & 5.15.2

Googled some info, but nothing really answers the question:

• Meaning of top, ascent, baseline, descent, bottom, and leading in Android's FontMetrics

• Qt Forum — Impossible to get true text hight with QFontMetrics/QFontMetricsF

• QTBUG-53271 — FontMetrics BoundingRect size is incorrect with chinese characters and any higher DPI text

As you can see below: green box is with metric height, while red is with bounding height. Sure, the bounding height does bound the entire text, but there is extra top and bottom spacing.

#include "mainwindow.h"#include "ui_mainwindow.h"#include <QPainter>#include <QFont>#include <QFontMetrics>MainWindow::MainWindow(QWidget *parent)    : QMainWindow(parent)    , ui(new Ui::MainWindow){    ui->setupUi(this);}MainWindow::~MainWindow(){    delete ui;}void MainWindow::paintEvent(QPaintEvent* event){    // Call base class implementation first    QMainWindow::paintEvent(event);    // Obtain the QPainter object    QPainter paint(this);    QFont font;    font.fromString("Apple LiGothic");    font.setPointSize(50);    QFontMetrics metric(font);    paint.setRenderHints(QPainter::TextAntialiasing | QPainter::Antialiasing, true);    paint.setFont(font);    paint.setPen(Qt::white);    const int align = Qt::AlignLeft | Qt::AlignTop | Qt::TextWordWrap;    QString text = "钳禾日当午";    QRect bound = metric.boundingRect(text);    bound = QRect(0, 0, bound.width(), bound.height());    QRect metricBound(0, 0, bound.width(), metric.height());    paint.translate(10, 100);    paint.setPen(Qt::red);    paint.drawRect(bound);    paint.setPen(Qt::green);    paint.drawRect(metricBound/*.adjusted(0,10,0,10)*/); // hack adjustment    paint.setPen(Qt::white);    paint.drawText(0, 0, bound.width(), bound.height(), align, text);    text = "汗滴禾下土";    bound = metric.boundingRect(text);    bound = QRect(0, 0, bound.width(), bound.height());    metricBound = QRect(0, 0, bound.width(), metric.height());    paint.translate(0, 100);    paint.setPen(Qt::red);    paint.drawRect(bound);    paint.setPen(Qt::green);    paint.drawRect(metricBound);    paint.setPen(Qt::white);    paint.drawText(0, 0, bound.width(), bound.height(), align, text);}