QT setting background image method

This article mainly introduces three kinds of Qt How to set the background picture ：

1、QPalette

2、 rewrite paintEvent

3、 Set up Qss(Qt style sheet)

1、QPalette

（1） Example

//.cpp


    this->resize(450,700);
    QPalette pa(this->palette());

    QImage img = QImage(":/img/01.jpg");
    img = img.scaled(this->size());


    QBrush *pic = new QBrush(img);

    pa.setBrush(QPalette::Window,*pic);

    //this->setAutoFillBackground(true);
    this->setPalette(pa);

QPalette Mainly through void QPalette::setBrush ( ColorRole role, const QBrush & brush ); Function to set the background image , among ColorRole Set to QPalette::window（ See for details QPalette Explanation ）. When setting the form background with the parent form , Need to add setAutoFillBackground(true) To display the background .

（2） Result chart

2、 rewrite paintEvent

all QWidget All subclasses of inherit QWidget Virtual function in ：[virtual protected] void QWidget::paintEvent(QPaintEvent *event). Rewrite the virtual function in the new form , You can finish setting the background of the form .

（1） Example

//.cpp




#include "pain.h"
#include <QPainter>
#include <QPixmap>
#include "palette.h"


Pain::Pain(QWidget *parent) : QWidget(parent)
{
    this->resize(450,700);
    this->setWindowTitle("PainEvent");
}


void Pain::paintEvent(QPaintEvent *event)
{
    QPainter *painter = new QPainter(this);

    QPixmap pic = QPixmap(":/img/03.jpg");
    //pic = pic.scaled(this->width(),this->height());

    painter->drawPixmap(0,0,this->width(),this->height(),pic);

}

In this case , rewrite paintEvent Event using QPainter Class void QPainter::drawPixmap(int x, int y, int w, int h, const QPixmap &pixmap, int sx, int sy, int sw, int sh) Method to set the background of the form .

（2） Result chart

3、 Set up Qss

Qss Use Qt The developed one is similar to Css The grammatical mechanism of , Can set various styles of forms . Form by using void setStyleSheet(const QString &sheet) To set and character string sheet Corresponding style . Concrete Qss Syntax mechanism can view help documents （Qt style sheet）.

（1） Example

//.cpp

#include "setstyle.h"
#include "pain.h"
#include <QFrame>

SetStyle::SetStyle(QFrame *parent) : QFrame(parent)
{
    this->resize(450,700);
    this->setWindowTitle("Qss");
    this->setStyleSheet("QFrame{background-image:url(:/img/02.jpg)}");
}

（2） Result chart

4、 The three methods are simply compared

You can set the background image using all three methods , But when the size of the form changes , The coverage of the background image will change .

（1）QPalette The set background image will overlap , Such as ：

 

（2）paintEvent The set picture will stretch and cover the form , Such as ：

（3） And set up Qss The above two coverage methods can be realized .

            When Qss Set to    background-image:url(:/img.jpg)  Then complete the overlapping coverage

             When Qss Set to    border-image:url(:/img.jpg)  Complete stretch coverage

 

This is my study notes , It may not be completely correct , For reference only ！

      Refer to the connection ：1、https://wenku.baidu.com/view/f5cdfdeaaeaad1f346933f27

                         2、https://blog.csdn.net/qq_25800311/article/details/80874757