Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface)

[K-Str]

Hi,
I'm quiet frustrated. Since a long time I try to install QT on an UBUNTU 18.04.3 Host cross compile for a raspberry3.
There are a lot of tipps and tutorials how to install the qt creator for cross compile and remote debugging for a raspberry but now works really for me.
I use a raspberry 3 where a LCD-display is connected via HDMI and SPI (for a touch pen). It runs a raspbian buster and the driver for the display.
The installation is qt 5.12.5 based on 5.13.1 and qt-creator 4.10.0.
The installation was fine and there where now errors during the installation.
But when I create a simple widget with some buttons (e.g. one push button and one radio butto) it handles only one button.
I get some errors when I run this widget

Unable to query physical screen size, defaulting to 100 dpi.
To override, set QT_QPA_EGLFS_PHYSICAL_WIDTH and QT_QPA_EGLFS_PHYSICAL_HEIGHT (in millimeters).
Attribute Qt::AA_ShareOpenGLContexts must be set before QCoreApplication is created.

but I cannot find any solution for them.
This is the code for the widget:
mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

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

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


void MainWindow::on_pushButton_clicked()
{
    qDebug() << "Hallo Pushy!";
}

void MainWindow::on_radioButton_clicked()
{
    qDebug() << "Hallo Radio!";
}

and mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

    void on_radioButton_clicked();

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

I'm sorry! sometimes I have the feeling sucessfull installing qt for creating widget for a raspberry never works and it's just a story like urban legends. Or does somebody really know a working tutorial or something?
It would be nice if I get an answer

thanks in advance!

[mrjj]

Hi

I understand your frustration. Cross compiling is often time consuming and hard to get working right.

I think you can just export the values
(in some .sh file to start app or in your profile so its always run)

export QT_QPA_EGLFS_PHYSICAL_WIDTH=520
export QT_QPA_EGLFS_PHYSICAL_HEIGHT=326

https://stackoverflow.com/questions/18518280/raspberry-pi-qt5-set-physical-screen-size

I liked this tutorial
https://mechatronicsblog.com/cross-compile-and-deploy-qt-5-12-for-raspberry-pi/

[K-Str]

@mrjj Thanks for your answer,
I'm sorry, it does not solve my problem.
When I make there is sitll only one button active, the second has ignored and I get this Error:

Attribute Qt::AA_ShareOpenGLContexts must be set before QCoreApplication is created.

[jsulm]

@K-Str Can you show your main.cpp file?

[K-Str]

@jsulm
Hello thanks for your answer,
Here you will find the main.cpp code:

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

[jsulm]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

it handles only one button

Does exact same application work properly on your host?
You're using auto-connect feature which is error-prone.

I don't think the warning you see is related to your problem. You probably can ignore the warning.

[K-Str]

@jsulm ,
yes I runned it on my host. Itworks perfectly!
Both buttons work.
When I start the widget on the raspberry from the command-line then it also shows this errors.
I think there went something wrong on the configuration during the installation.
I Installed it using almost this Tutorial link text.
I also installed qt on a raspberry and it also works without any problems.

If you need I can insert the installationscripte for the raspberry and Linux host.

[jsulm]

@K-Str I really don't know why this happens. Alternative approach would be to not to use auto-connect feature (it is error-probe anyway). Instead give your slots a bit different names and connect them manually with signals.

[K-Str]

@jsulm Thanks your answer.
I will try it.
But

• 1. How cann I connect the signals manually to a slot?
• 2. How do I prevent of auto-connection?

Could you give me a hint how to do it?

[jsulm]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

How cann I connect the signals manually to a slot?

Using connect(). https://doc.qt.io/qt-5/signalsandslots.html

"How do I prevent of auto-connection?" - do not use the naming convention (like on_pushButton_clicked()) - rename your slots to for example pushButtonClicked()

[K-Str]

@jsulm ,
I use the qt-creator module to create form sheets.
Does it not work ? Must I setup everything without using the form file(=.ui)?
What is the problem? because I can create and run the widget on the host PC.
Do you think this is more a problem of the Touch-screen drivers?
Has anybody a idea?

[jsulm]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

Does it not work ?

It does. What sometimes causes problems is the auto-connect feature - I was only talking about this and not whole Qt Designer (ui).

[K-Str]

@jsulm ,
hi,
Thanks a lot for your answer!
Sorry for this delay but I was involved in an other project.
I use Qt5.10.1! and make a new widget.

• Here I open forms --> MainWindow.ui
  

• Next I create two button
  

• then I execute go to slot
  

• this makes a new slot:
  mainwindow.cpp
  
  and mainwindow.h
  
  Where must I modify the names? In both files mainwindow.cpp and mainwindow.h

[jsulm]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

Where must I modify the names?

This way you probably can't as designer generates the slot for you.
I create slots by myself, so can name them as I lake.

[K-Str]

@jsulm ,
hi,
I just renamed it as follows:
mainWindow.cpp

and mainwindow.h

It still doesn't work.
It is frustrating!
Was here something wrong?
What does it mean "You create your slots by yourself"?

[jsulm]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

You create your slots by yourself

You write the code by yourself.
If you renamed the slot then you have to connect signal and slot manually now:

connect(ui->pushButton, &QPushButton::clicked, this, MainWindow::MyPushButtonClicked);

Please take a look at https://doc.qt.io/qt-5/signalsandslots.html

[K-Str]

@jsulm
I'm really sorry but it's crazy.
When I go forward step by step you get again new errors.
I made it as you suggested but I get new problems:
I think I yuse this connect command in a wrong way:

When I compile it I get this errors:

/home/kurt/qt-projekte/AsimpleWidget/mainwindow.cpp:9: error: invalid use of void expression
     connect(ui->MyPushButton, &QPushButton::clicked, this, MainWindow::MyPushButtonClicked());

and

/home/kurt/qt-projekte/AsimpleWidget/mainwindow.cpp:10: error: invalid use of void expression
     connect(ui->MyRadioButton,&QRadioButton::clicked, this, MainWindow::MyRadioButtonClicked());

I think this void makes some problems.
Thanks for a hint whats wrong

[mrjj]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

MainWindow::MyRadioButtonClicked()

Hi
in the connect you should not have the ()
MainWindow::MyRadioButtonClicked**()**
when using the new syntax. ( the one with no SIGNAL and SLOT macros)

connect(ui->MyRadioButton,&QRadioButton::clicked, this, MainWindow::MyRadioButtonClicked); // no () in the end

[K-Str]

Hi @jsulm ,
I think it's like Sisyphean task because I f you solve one problem you get the next one.
Thank you for your patience. But I got the next problem:

/home/kurt/qt-projekte/AsimpleWidget/mainwindow.cpp:9: error: no matching function for call to ‘MainWindow::connect(QPushButton*&, void (QAbstractButton::*)(bool), MainWindow* const, <unresolved overloaded function type>)’
     connect(ui->MyPushButton, &QPushButton::clicked, this, MainWindow::MyPushButtonClicked);

and

/opt/qt5pi/sysroot/usr/local/qt5pi/include/QtCore/qobject.h:275: error: no type named ‘type’ in ‘struct std::enable_if<false, QMetaObject::Connection>’

Now seems to be something wrong in the sysroot?

[mrjj]

@K-Str said in Has anyone ever got a widget running on a rpi3 with LCD-Display (HDMI and SPI-Interface):

connect(ui->MyPushButton, &QPushButton::clicked, this, MainWindow::MyPushButtonClicked);

Hi
You are missing a & ( sorry my bad, i missed it before)

connect(ui->MyPushButton, &QPushButton::clicked, this, -->& MainWindow::MyPushButtonClicked);