how do you recalibrate touch events for a Qt application?

Question

I have a simple Qt5.2 application it's built for the TI AM335x EVM (ARM based processor). It just has 1 button on it which enables some LEDs on the board.

The problem I'm having is that the touch event is not calibrated to the screen. Example:

*************
*           *
*  []       *
*       X   *
*           *
*************

So if the [] is where the button is, the X is where you have to touch to activate it. It's like it's upside down and backwards. I've tried with larger applications (more buttons) and the trend follows.

Now when I use the Qt4.8 GUI user interface provided by TI, the touch works as expected, so for some reason when I compile by 5.2 code it seems like it needs to be recalibrated, but I'm not sure how to do that.

My questions:

1. Has anyone working with Qt run into anything like this in the past?
2. Anyone who knows Qt know if there is an ability to recalibrate programmatically? (I can't seem to find anything about this on the Qt site)

---

Additional information that may or may not be helpful:

My Qt environment was configured with this command:

./configure -prefix /usr/Qt5.2 -xplatform linux-am335x-g++ -no-sse -no-sse2 -no-glib -no-cups -no-largefile -no-accessibility -no-openssl -no-gtkstyle -opensource

Followed by a make and make install. My path is updated to include the correct version of the TI toolchain and the home configured/built version of qmake:

mike@mike-VirtualBox:/usr/Qt5.2/test_button$ echo $PATH
/usr/Qt5.2/bin: /home/mike/ti-sdk-am335x-evm-06.00.00.00/linux-devkit/sysroots/i686-arago-linux/usr/bin:/usr/local/Trolltech/Qt-4.8.5/bin:/home/mike/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/mike/bin

Flags used in the actual compile command:

arm-linux-gnueabihf-g++ -c -march=armv7-a -marm -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a8 -O2 -Wall -W -D_REENTRANT -fPIE -DQT_NO_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../mkspecs/linux-am335x-g++ -I. -I. -I../include -I../include/QtWidgets -I../include/QtGui -I../include/QtCore -I. -o main.o main.cpp

The application is launched with:

./touch_keys -platform eglfs

The application:

main.cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWindow;
    mainWindow.showMaximized();
    return app.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include <QtCore/QCoreApplication>
#include <QDebug>
#include <QFile>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    // Create the button, make "this" the parent
    m_button = new QPushButton("Light LEDs", this);

    // set size and location of the button
    m_button->setGeometry(QRect(QPoint(100, 100),
                                 QSize(200, 50)));

    // Connect button signal to appropriate slot
    connect(m_button, SIGNAL(released()), this, SLOT(handleButton()));
}

void MainWindow::handleButton()
{
    char buf[10];
    // change the text
    m_button->setText("Boom");

    // resize button
    m_button->resize(100,100);
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPushButton>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
private slots:
    void handleButton();
private:
    QPushButton *m_button;
};

#endif // MAINWINDOW_H

Answer 1

So I found out that the touch support via tslib should not be required when using the eglfs platform plugin. eglfs has the evdev input handlers built-in so mouse/keyboard/touch support come without needing anything else to connect to the correct device.

This means that evdevtouch is failing to recognize the touch screen on am335x, this was supposed to be corrected in 5.2, but clearly still isn't. The "fix" (workaround) is to flip the screen manually by exporting an QPA environment variable:

export QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS="rotate=180" 

This properly transforms the coordinates.