请教为什么在WINDOWS上通过QT绘制的字体的坐标不对

#include "stdafx.h"
#include <QCoreApplication.h>
#include <QApplication.h>
#include <QPixmap.h>
#include <QPainter.h>
#include <iostream>
#include "qtextcodec.h "
#include "qobject.h"
using namespace std;

#ifdef _DEBUG
#pragma comment(lib,"QtCored4.lib")
#pragma comment(lib,"QtGuid4.lib")
#else
#pragma comment(lib,"QtCore4.lib")
#pragma comment(lib,"QtGui4.lib")
#endif

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QPainter qPaint;
    QPixmap *qPixmap = new QPixmap(700,500);
    qPixmap->fill(Qt::green);
    qPaint.begin(qPixmap);
    qPaint.setRenderHint(QPainter::Antialiasing, true);
    QPen pen(QColor(255,0,0),1);
    qPaint.setPen(pen);
    QString string = "我是中国人";
    QTextCodec* gbk_codec = QTextCodec::codecForName("system");
    QString gbk_string = gbk_codec->toUnicode(string.toLatin1());
    
    QFont font;
    font.setFamily("宋体");
    font.setPixelSize(100);
    QFontMetricsF fontMetrics(font);
    QRectF rect = fontMetrics.boundingRect(QString("我是中国人"));
    qPaint.setFont(font);
    qPaint.drawText(0,200,gbk_string);
    qPaint.drawRect(0,100,500,100);

         //依次绘制单个字体，以确认SetPointSize和SetPixelSize()
    gbk_string = gbk_codec->toUnicode("我");
    qPaint.drawText(0,400,gbk_string);
    gbk_string = gbk_codec->toUnicode("是");
    qPaint.drawText(100,400,gbk_string);
    gbk_string = gbk_codec->toUnicode("中");
    qPaint.drawText(200,400,gbk_string);
    gbk_string = gbk_codec->toUnicode("国");
    qPaint.drawText(300,400,gbk_string);
    gbk_string = gbk_codec->toUnicode("人");
    qPaint.drawText(400,400,gbk_string);
    qPaint.drawRect(0,300,500,100);

    qPaint.end();
    qPixmap->save("C:/a.jpg","JPEG");
    qPixmap->save("C:/a.png","PNG");
    qPixmap->save("C:/a.gif","GIF");
    qPixmap->save("C:/a.bmp","BMP");
    if(qPixmap)
    {
        delete qPixmap;
        qPixmap = NULL;
    }
    return a.exec();
    return 0;
}