Qt图片按原比例缩放

QString strFilePath = QFileDialog::getOpenFileName(this, tr("Select file"), QStandardPaths::standardLocations(QStandardPaths::PicturesLocation), "*.png *.jpg");
if (strFilePath.isEmpty())
{
return;
}

QImageReader imgReader;
imgReader.setFileName(strFilePath);
if (!imgReader.canRead())
{
QMessageBox::information(, "", QObject::tr("The image data is corrupt, Please select a valid one!"));
return;
}

int nThumbnailWidth = ;
int nThumbnailHeight = ;
QLable *pThumbLab = new QLabel(this);
pThumbLab->setFixedSize(nThumbnailWidth, nThumbnailHeight);QSize sizeImage = imgReader.size();
QPixmap pixThumb(mstrPicPath);
if (sizeImage.width() > nThumbnailWidth || sizeImage.height() > nThumbnailHeight)
{
if (sizeImage.width() > sizeImage.height())
{
pixThumb = pixThumb.scaledToWidth(nThumbnailWidth, Qt::SmoothTransformation);
}
else
{
pixThumb = pixThumb.scaledToHeight(nThumbnailHeight, Qt::SmoothTransformation);
}
pThumbLab->setFixedSize(pixThumb.size());
}
else
{
pThumbLab->setFixedSize(sizeImage);
}
pThumbLab->setPixmap(pixThumb);