Is allow to use the QDrag class in Qt Webassembly?

Yash001 · wrote on 7 Jul 2023, 19:14

Application is hang whenever it is reach to line drag->exec(Qt::CopyAction | Qt::MoveAction);

It is work fine with mingw, msvc compiler.
It is not work in brower.
Using:
Qt 6.5.1
emsdk 3.1.25

#include "ElementDragEventHandler.h"

#include "AbstractElement.h"

#include <qevent.h>
#include <qlabel.h>
#include <qdrag.h>
#include <qmimedata.h>



bool ElementDragEventHandler::eventFilter(QObject* watched, QEvent* event)
{

    if (event->type() == QEvent::MouseButtonPress) {

        QWidget* label = qobject_cast<QWidget*>(watched);
        if (label && label->property("element").isValid()) {

            // Get the element data stored in the label
            AbstractElement* element = qvariant_cast<AbstractElement*>(label->property("element"));

            // Create a drag object
            QDrag* drag = new QDrag(label);
            QMimeData* mimeData = new QMimeData;

            // Set the element as the mime data
            mimeData->setProperty("element", QVariant::fromValue(element));

            drag->setMimeData(mimeData);

            // Set the drag pixmap
            QPixmap pixmap = element->getImage().scaled(90, 90); // Adjust the size as needed
            drag->setPixmap(pixmap);


            // Start the drag
            drag->exec(Qt::CopyAction | Qt::MoveAction);
            return true;
        }
    }

    return QObject::eventFilter(watched, event);
}

anything I need to change.

# Define the project name and version
TEMPLATE = app
TARGET = myApp
VERSION = 0.1.0

# Define the target platform and architecture
QMAKE_TARGET.arch = wasm

# Set the C++ version and compiler flags
CONFIG += c++17
QMAKE_CXXFLAGS += -std=c++17

# Enable precompiled headers
#PRECOMPILED_HEADER = $$PWD/src/pch.h

# Define the source files
SOURCES += $$PWD/src/main.cpp ......
           

# Define the header files
HEADERS += $$PWD/src/MainWindow.h ....
          

# Define the resource files
RESOURCES += $$PWD/src/resources.qrc

# Include the required Qt modules
QT += core gui widgets

# WebAssembly-specific settings
wasm {
    # Set the output directory for WebAssembly build
    DESTDIR = $$PWD/build-wasm

    # Enable WebAssembly support
    CONFIG += wasm

    # Include the Emscripten libraries
    INCLUDEPATH += $$PWD/3rdParty/emsdk/upstream/emscripten/system/include
    LIBS += -L $$PWD/emsdk/upstream/emscripten/system/lib \
            -lglut -lGLU -lGL

    # Set the deployment directory for WebAssembly build
    QMAKE_PREFIX_PATH += $$PWD/build-wasm/qtbase

    # Link against the Emscripten libraries
    LIBS += -s USE_GLFW=3 -s WASM=1 -s USE_WEBGL2=1 -s PTHREAD_POOL_SIZE=100

    # Add WebAssembly-specific compiler flags
    QMAKE_CXXFLAGS += -s FORCE_FILESYSTEM=1
}

# Link against the Qt libraries
LIBS += -L "C:/Qt6/6.5.1/wasm_multithread/lib/libQt6Core.a" -L "C:/Qt6/6.5.1/wasm_multithread/lib/libQt6Gui.a" -L "C:/Qt6/6.5.1/wasm_multithread/lib/libQt6Widgets.a"

lorn.potter · wrote on 10 Jul 2023, 23:54

Drag and drop has never worked very well in QtWebAssembly.
But it is working in 6.6.0beta1 single threaded release.

You need to use asyncify though:
https://doc.qt.io/qt-6/wasm.html#asyncify

Good news is, you no longer have to rebuild Qt to get asyncify, you just need to add a linker argument.
cmake: target_link_options(<target> PUBLIC -sASYNCIFY -Os)
qmake: QMAKE_LFLAGS += -sASYNCIFY -Os