QT displays the specified position and size of the picture

Sometimes we need to cut the picture without cutting it , Display the area specified by the picture ,qt There are two ways to do this ：
First use qss To achieve .
The second method uses drawing events to achieve .
Original picture ：

Now we need to show its central position , But the length and width of the display area are different from the original image , The width is less than the width we want to display , The height should be greater than the height we show , At this time, you need to enlarge the picture according to the width scale , Then calculate according to the width proportion y The location of , from y Take the middle area .
qss Realization ：
m_btn = new QPushButton(this);
m_btn->resize(392,220); // Display area
QPixmap pixmap("/home/yjd/yjd/test/MypixPos/2.jpg"); // Use QPixmap perhaps QImage To get the width and height of the picture .
int y = (pixmap.height()392.00/pixmap.width() - 220)/2pixmap.width()/392.00;// Calculation y The location of
QString pix = “border-image:url(/home/yjd/yjd/test/MypixPos/2.jpg)”;
QString pixstyle = QString("%1 %2 0 %3 0").arg(pix).arg(y).arg(y);//qss This way is to take the picture distance 、 Right 、 Next 、 Left position .
m_btn->setStyleSheet(pixstyle);

Draw event implementation ：
QPainter p(this);
QPixmap pixmap("/home/yjd/yjd/test/MypixPos/2.jpg");
pixmap = pixmap.scaled(392,392.00/pixmap.width()*pixmap.height());// Enlarge in proportion to the width
p.drawPixmap(QRect(0,0,392,220),pixmap,QRect(0,(pixmap.height() - 220)/2,392,220));// first Rect Is the display area , the second Rect Is to take which area in the picture .

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    
    ui->setupUi(this);

    m_btn = new QPushButton(this);
    m_btn->resize(392,220);

// m_btn->setStyleSheet("background-image: url(/home/yjd/yjd/test/MypixPos/1.jpg);"
// "background-repeat:no-repeat;"
// "background-position:center;"
// "background-origin:border;");

    QPixmap pixmap("/home/yjd/yjd/test/MypixPos/2.jpg");
    int y = (pixmap.height()*392.00/pixmap.width() - 220)/2*pixmap.width()/392.00;
    qWarning()<<"------------"<<pixmap.height()<<pixmap.width()<<y;
    QString pix = "border-image:url(/home/yjd/yjd/test/MypixPos/2.jpg)";
    QString pixstyle = QString("%1 %2 0 %3 0").arg(pix).arg(y).arg(y);
    m_btn->setStyleSheet(pixstyle);


    m_lab = new QLabel(this);
    m_lab->setGeometry(0,230,392,400*392.00/225);
    m_lab->setStyleSheet("border-image:url(/home/yjd/yjd/test/MypixPos/2.jpg)");
}

Widget::~Widget()
{
    
    delete ui;
}


void Widget::paintEvent(QPaintEvent *event)
{
    
    QPainter p(this);
    QPixmap pixmap("/home/yjd/yjd/test/MypixPos/2.jpg");
    pixmap = pixmap.scaled(392,392.00/pixmap.width()*pixmap.height());
    p.drawPixmap(QRect(0,0,392,220),pixmap,QRect(0,(pixmap.height() - 220)/2,392,220));
}