Qt and OpenCv CrossCompile for Raspberry Pi Error - qt

Question

I'm trying to use opencv in a QT project for a raspberry pi 4. I'm on a Linux machine
Here is my .pro file and errors I get. And my mainwindow.cpp
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
CONFIG += c++17
# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0
SOURCES += \
main.cpp \
mainwindow.cpp
HEADERS += \
mainwindow.h
FORMS += \
mainwindow.ui
TRANSLATIONS += \
SCWWS_fr_FR.ts
CONFIG += lrelease
CONFIG += embed_translations
# Default rules for deployment.
qnx: target.pHere is my mainwindow.cppath = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target
RESOURCES += \
resources.qrc
unix:!macx: LIBS += -L$$PWD/../../Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/lib/arm-linux-gnueabihf -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs -lopencv_shape -lopencv_videoio
INCLUDEPATH += $$PWD/../../Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/include
DEPENDPATH += $$PWD/../../Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/include
Here is my mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QtCore>
#include <QFontDatabase>
#include <QDebug>
#include <QImage>
//#include "opencv2/core.hpp"
//#include "opencv2/highgui.hpp"
//using namespace cv;
mainwindow::mainwindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::mainwindow)
{
QFontDatabase::addApplicationFont(":/fonts/roboto-light.ttf");
ui->setupUi(this);
qDebug() << "Hello World !";
//cv::VideoCapture camera = VideoCapture(0);
//
//Mat frame;
//camera >> frame;
//QImage img(frame.data, frame.cols, frame.rows, frame.step, QImage::Format_RGB888);
//ui->label->setPixmap(QPixmap::fromImage(img));
}
mainwindow::~mainwindow()
{
delete ui;
}
And here are errors I get
libXinerama.so.1, needed by /home/lolix/Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/lib/arm-linux-gnueabihf/libgdk-3.so.0, not found (try using -rpath or -rpath-link)
libmmal_core.so, needed by /home/lolix/Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/lib/arm-linux-gnueabihf/libavcodec.so.58, not found (try using -rpath or -rpath-link)
libmmal_vc_client.so, needed by /home/lolix/Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/lib/arm-linux-gnueabihf/libavcodec.so.58, not found (try using -rpath or -rpath-link)
.
.
.
liblapack.so.3, needed by /home/lolix/Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/lib/libarmadillo.so.9, not found (try using -rpath or -rpath-link)
/home/lolix/Documents/Qt-CrossCompile-RaspberryPi/raspberrypi4/sysroot/usr/lib/arm-linux-gnueabihf/libopenmpt.so.0:-1: error: undefined reference to `std::random_device::_M_getentropy() const#GLIBCXX_3.4.25'
Errors arrives has soon has I uncomment my code. The version of open cv on the RP4 is 3.2 and when I install it on my machine it's 4.5. Event if I use the same command sudo apt-get install libopencv-dev
Thanks for your help
**EDIT**
I was able to get rid of these errors with this response. But a new one appeared
undefined reference to std::random_device::_M_getentropy() const#GLIBCXX_3.4.25

Answer 1

Regarding OpenCV I suggest to build it from source, for the RPi I always cross-compile using docker, as described here (just remove the references to openvino).
At this point you also need to cross-compile Qt for the RPi, but I guess you already did it.