i want to read some exif informations with QExifImageHeader (from the QT Extended Library)
(see here)
Can someone say me how to get the informations from one tag?
I have this code:
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QExifImageHeader header;
header.loadFromJpeg("test.jpg");
QExifValue value=header.value(QExifImageHeader::ImageWidth );
qDebug()<<value.toByte();
return a.exec();
}
The result of the qDebug() is "0". But why?
I saw some other librarys (like exiv2). But they are to heavy for my project.
Greetings
Related
Searching for an alternative to Qt's official VirtualKeyboard I came across this MockupVirtualKeyboard repository. It is based on QPlatformInputContext. I build and installed the plugin to Qt5.15.2/plugins/platforminputcontexts, but I dont know how to bring the Virtual Keyboard up.
What I would like to achieve, using QML, is:
TextInput{
text: ""
onFocusChanged: showVirtualInput()
}
If you want to use the keyboard then you must set the environment variable "QT_IM_MODULE" to be "mockup", and you can do that by placing the following line of code in the main.cpp:
int main(int argc, char *argv[])
{
qputenv("QT_IM_MODULE", QByteArray("mockup"));
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
QGuiApplication app(argc, argv);
# ...
On the other hand, you must change:
Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QPlatformInputContextFactoryInterface" FILE "mockup.json")
to
Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QPlatformInputContextFactoryInterface.5.1" FILE "mockup.json")
in the mockupplatforminputcontextplugin.h file, recompile and install the file so that it is compatible with Qt 5.15.2
With the following code:
#include <QApplication>
#include <QWebEngineView>
#include <QWebEngineProfile>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWebEngineView w;
QObject::connect(w.page(), &QWebEnginePage::featurePermissionRequested, [&](const QUrl &securityOrigin, QWebEnginePage::Feature feature)
{
w.page()->setFeaturePermission(securityOrigin, feature, QWebEnginePage::PermissionGrantedByUser);
});
w.setUrl(QUrl("https://mycurrentlocation.net/"));
w.show();
return a.exec();
}
and a USB dongle connected to my 64bit Archlinux system (with geoclue2 installed and working), I don't get the correct geolocation coordinates (which I get on the same website with Google Chrome).
There are both in France but 200km apart.
Update 1:
A similar issue with the same coordinates seems to appear when centering on my position with a QML Map componenent.
Do I need to setup something in order for it to work ?
The issue is not Qt related.
/usr/lib/geoclue-2.0/demos/where-am-i
returns wrong coordinates.
I need help in writing my static text to image file without using "QApplication app(argc, argv);" in main(). My version of QT is 5.12.2.
Currently I'm able to do this with the below code:
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QCoreApplication::addLibraryPath("./plugins");
QString imagePath(QStringLiteral("./images/output/testOutput1.png"));
QImage image(500, 400, QImage::Format_RGB888);
image.fill(Qt::red);
QPainter painter;
if (!painter.begin(&image))
return;
painter.setPen(QPen(Qt::black));
painter.setFont(QFont("Times", 12, QFont::Bold));
painter.drawText(image.rect(), Qt::AlignCenter, "writing text on image");
painter.end();
image.save(imagePath);
return 0;
}
I'm trying to get a similar type solution which does not uses "QApplication app(argc, argv);" in my code.
Currently if I remove the deceleration of "QApplication app(argc, argv);" my code crashes at "painter.drawText(...);".
The most you can do is to exchange the QApplication for a QGuiApplication (thus avoiding the useless dependency from the QtWidgets module).
Qt initializes most of its static/global stuff inside the bowels of QCoreApplication (for QtCore stuff)/QGuiApplication (for QtGui stuff)/QApplication (for QtWidgets stuff); each derives from the other, so if you have a QApplication you already have all the stuff from Gui and Core.
The font engine (and other paint-related stuff) is initialized inside the QGuiApplication constructor, as hinted in QFont documentation
Note that a QGuiApplication instance must exist before a QFont can be used.
so you are not going to paint without instantiating it (or a class derived from it).
I'm making a simple Qt app that reads stuff from a CSV file and generates a PCAP data file out of it for reading by some other software.
And so soon as I invoque pcap_open_dead, pcap_dump_open or pcap_dump, I get no more console output upon running my small converter. Even the Hello World that comes at the beginning of the main doesn't show up any more. From the code below, if I simply comment out those three methods, the console output and "Hello World" come back.
Being new and therefore clueless about pcap, I ask for help.
#include <QCoreApplication>
#include <iostream>
#include "pcap.h"
using namespace std;
struct pcapWriter_S
{
bool isAvailable;
int m_OutPcapIpId;
pcap_t* m_OutPcapHandle;
pcap_dumper_t* m_OutPcapFile;
}m_pcapWriter;
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
cout << "Hello World!" << endl;
//m_pcapWriter.m_OutPcapHandle = pcap_open_dead(DLT_EN10MB,65535);
//m_pcapWriter.m_OutPcapFile = pcap_dump_open(m_pcapWriter.m_OutPcapHandle, QString("tmp_csv_out.pcap").toAscii().data());
m_pcapWriter.m_OutPcapIpId = 1;
if (m_pcapWriter.m_OutPcapFile != 0)
{
m_pcapWriter.isAvailable = true;
}
QByteArray pkt_data;
// Omitted code to generate pkt data from input file
m_pcapWriter.m_OutPcapIpId++;
//pcap_dump((unsigned char*)m_pcapWriter.m_OutPcapFile, &header, (unsigned char*)pkt_data.data());
return a.exec();
}
Somehow this was due to me calling pcap_open but not pcap_close quite yet. In between console stuff gets lost - can't swear it gets written on the pcap thing but it blocks the console anyway.
The code
#include <QtCore>
#include <QtXml/QDomElement>
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
QDomElement* element = new QDomElement();
element->setTagName("feature");
qDebug() << element->tagName();
return app.exec();
}
prints simply "". However, as far as I can tell from the documentation it should print "feature". In fact
qDebug() << element->isNull();
prints true so something is not being set correctly. Does anyone know what I am doing wrong?
I'm using Qt 4.6.3 on openSUSE Linux 11.2.
You cannot use the default constructor. You need to use QDomDocument::createElement(const QString &tagName). The element needs to be part of a document. You cannot use it "standalone".
Here's what the documentation says for the QDomElement default constructor:
QDomElement::QDomElement ()
Constructs an empty element. Use the QDomDocument::createElement() function to construct elements with content.
By "empty" they mean null.