[FIXED] How to restrain mouse cursor from leaving a QWidget area in PySide2

Issue

I have a widget containing two buttons that can be (drag and drop) swapped using the mouse middle button. I am trying to restrain the mouse cursor from leaving the QWidget area when dragging and dropping a Qpushbutton... I am using dragMoveEvent() which offsets the cursor every time it crosses the border of the widget. It works when you move the mouse slowly but fast movements will make the cursor leave the area. What is the best way to make this happen? Thanks.

PS: Go to the Drag and Drop area for reference

import os
import random
import sys
import time
from PySide2 import QtOpenGL
from PySide2 import QtWidgets
from PySide2.QtCore import QEvent, QMimeData, QPoint, QRect
from PySide2.QtGui import QCursor, QDrag, QWindow
# import nuke
# import nukescripts
from collapse import Collapse
try:
    from PySide import QtGui, QtCore
except ImportError:
    from PySide2 import QtCore
    from PySide2 import QtWidgets as QtGui
    from PySide2 import QtGui as QtG

class CreateNodeBoard(QtGui.QWidget):
    def __init__(self, parent = None):
        QtGui.QWidget.__init__(self, parent)
        
        self.nukePathSeparator = "/"
        #self.toolPath = self.getFullPathWithExt()
        self.currentDir = os.path.dirname(os.path.realpath(__file__))

    ################################################################################
    # GUI
    ################################################################################
        self.setMinimumWidth(350)        
        self.mainLayout = QtGui.QVBoxLayout()
        self.mainLayout.setSpacing(0)
        self.mainLayout.setAlignment(QtCore.Qt.AlignTop)
        self.setLayout(self.mainLayout)
        self.target = None
        self.setAcceptDrops(True)
        
        self.nodeBoardWidget = QtGui.QWidget()
        self.nodeBoardWidget.setAcceptDrops(True)
        nodeBoardVLayout = QtWidgets.QVBoxLayout()
        self.nodeBoardWidget.setLayout(nodeBoardVLayout)

        self.userButtonLayout = QtGui.QGridLayout()
        nodeBoardVLayout.addLayout(self.userButtonLayout)
        button1 = QtWidgets.QPushButton("a")
        button2 = QtWidgets.QPushButton("b")
        self.userButtonLayout.addWidget(button1)
        self.userButtonLayout.addWidget(button2)
        self.userButtonLayout.setAlignment(QtCore.Qt.AlignLeft)

        self.mainLayout.addWidget(self.nodeBoardWidget)
    def get_index(self, pos):
        for i in range(self.userButtonLayout.count()):
            buttonGlob = self.userButtonLayout.itemAt(i).widget().mapToGlobal(QPoint(0,0)) 
            if QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(pos) and i != self.target:
                return i
    
    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.MiddleButton:           
            self.target = self.get_index(QCursor.pos())
        else:
            self.target = None
    
    def mouseMoveEvent(self, event):        
        if event.buttons() & QtCore.Qt.MiddleButton and self.target is not None:
            print("moving")
            drag = QDrag(self.userButtonLayout.itemAt(self.target).widget())
            pix = self.userButtonLayout.itemAt(self.target).widget().grab()
            mimedata = QMimeData()
            mimedata.setImageData(pix)
            drag.setMimeData(mimedata)
            drag.setPixmap(pix)
            drag.setHotSpot(QPoint(40,10))
            drag.exec_()
            
    def dragMoveEvent(self, event):
        cursorPos = QCursor.pos()
        widgetPos = self.nodeBoardWidget.mapToGlobal(QPoint(0,0))
        if cursorPos.x() < widgetPos.x() or cursorPos.y() < widgetPos.y():
           QCursor.setPos(QCursor.pos().x() + 1 , QCursor.pos().y() + 1 )
        event.accept()
    

    def dragEnterEvent(self, event):
        print("drag enter event")
        if event.mimeData().hasImage():
              event.accept()
        else:
            event.ignore()
    

    def dropEvent(self, event):
        print("drop")
        buttonGlob = self.userButtonLayout.itemAt(self.target).widget().mapToGlobal(self.pos())
        if not QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(QCursor.pos()):
            source = self.get_index(QCursor.pos())
            if source is None:
                return

            i, j = max(self.target, source), min(self.target, source)
            p1, p2 = self.userButtonLayout.getItemPosition(i), self.userButtonLayout.getItemPosition(j)

            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(i), *p2)
            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(j), *p1)
            self.target = None

app = QtWidgets.QApplication(sys.argv)

# Create a Qt widget, which will be our window.
window = CreateNodeBoard()
window.show()  # IMPORTANT!!!!! Windows are hidden by default.

# Start the event loop.
app.exec_()

---

EDIT

---

So after further investigation and testing the code on both LINUX/WINDOWS I have come to the conclusion that both behaviours are caused by the programme exceeding the maximum recursion limit. Any time the mouse cursor during the drag event leaves the assigned widget something causes the events to call each other and this causes my app to crash. Having this as a standalone app does not cause any problem and I do not know why? Also, I have no ideas how this programme goes into recursion.

The previous solution of mine where I tried to create a "safe zone" for the mouse did not solve the issue as far as there are certain mouse movements causing the same bug.

Here is a better version of a working code. As I have already mentioned it works as a standalone GUI but causes the programme to crash within another software environment.

from __future__ import print_function

import sys

try:
    from PySide import QtWidgets, QtCore
except ImportError:
    from PySide2 import QtCore
    from PySide2 import QtWidgets
    from PySide2 import QtGui
    from PySide2 import QtOpenGL


class CreateNodeBoard(QtWidgets.QWidget):
    def __init__(self, parent=None):
        QtWidgets.QWidget.__init__(self, parent)

    ################################################################################
    # GUI
    ################################################################################

        self.setMinimumWidth(350)
        self.mainLayout = QtWidgets.QVBoxLayout()
        self.mainLayout.setSpacing(0)
        self.mainLayout.setAlignment(QtCore.Qt.AlignTop)
        self.setLayout(self.mainLayout)
        self.target = None
        self.targetWidget = None
        self.setAcceptDrops(True)

    ################################################################################
    # GUI - NODE BOARD
    ################################################################################

        # Create a Layout to hold all widgets
        self.nodeBoardWidget = QtWidgets.QWidget()
        self.nodeBoardWidget.setAcceptDrops(True)
        nodeBoardVLayout = QtWidgets.QVBoxLayout()
        self.nodeBoardWidget.setLayout(nodeBoardVLayout)

        # create a grid layout inside nodeBoaardVLayout and load buttons from JSON
        self.userButtonLayout = QtWidgets.QGridLayout()
        nodeBoardVLayout.addLayout(self.userButtonLayout)

        button1 = QtWidgets.QPushButton('button1')
        self.userButtonLayout.addWidget(button1)

        button2 = QtWidgets.QPushButton('button2')
        self.userButtonLayout.addWidget(button2)

        button3 = QtWidgets.QPushButton('test button')
        button3.clicked.connect(self._test)
        self.userButtonLayout.addWidget(button3)

        self.userButtonLayout.setAlignment(QtCore.Qt.AlignLeft)
        self.mainLayout.addWidget(self.nodeBoardWidget)
        nodeBoardVLayout.addStretch(1)

    ############################################################################
    # test
    ############################################################################

    def _test(self):
        print(self.topLevelWidget())

    def dragLeaveEvent(self, event):
        print("dragLeaveEvent :", event)

        # XXX: does not work on macOS
        # self.drag.cancel()

        # parent = self.parent().mapToGlobal(self.drag.hotSpot())
        # QtGui.QCursor.setPos(parent.x() + 50, parent.y() + 50)

        # XXX: could still causes a crash
        # q = QMessageBox()
        # q.setText('no can do')
        # q.exec_()

    def leaveEvent(self, event):
        pass

    def enterEvent(self, event):
        pass

    ################################################################################
    # DRAG AND DROP
    ################################################################################

    def get_index(self, pos):
        for i in range(self.userButtonLayout.count()):
            buttonGlob = self.userButtonLayout.itemAt(
                i).widget().mapToGlobal(QtCore.QPoint(0, 0))
            if QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(pos) and i != self.target:
                return i

    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.MiddleButton:
            self.target = self.get_index(QtGui.QCursor.pos())

        else:
            self.target = None

    def mouseMoveEvent(self, event):

        if event.buttons() and QtCore.Qt.MiddleButton and self.target is not None:
            print("mouseClickEvent :", event)

            self.drag = QtGui.QDrag(
                self.userButtonLayout.itemAt(self.target).widget())
            pix = self.userButtonLayout.itemAt(self.target).widget().grab()
            mimedata = QtCore.QMimeData()
            mimedata.setImageData(pix)
            self.drag.setMimeData(mimedata)
            self.drag.setPixmap(pix)
            self.drag.setHotSpot(QtCore.QPoint(40, 10))
            self.drag.exec_()

    def dragMoveEvent(self, event):
        # print("dragMoveEvent :", event)
        cursorPos = QtGui.QCursor.pos()
        widgetPos = self.nodeBoardWidget.mapToGlobal(QtCore.QPoint(0, 0))
        if cursorPos.x() <= widgetPos.x() or cursorPos.y() <= widgetPos.y():
            QtGui.QCursor.setPos(QtGui.QCursor.pos().x() +
                                 10, QtGui.QCursor.pos().y() + 10)

    def dragEnterEvent(self, event):
        print("dragEnterEvent :", event)
        # XXX: if ignored, will not crash but will not propagate events
        event.accept()

    def dropEvent(self, event):
        # print("dropEvent :", event)
        buttonGlob = self.userButtonLayout.itemAt(
            self.target).widget().mapToGlobal(self.pos())
        if not QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(QtGui.QCursor.pos()):
            source = self.get_index(QtGui.QCursor.pos())
            if source is None:
                return

            i, j = max(self.target, source), min(self.target, source)
            p1, p2 = self.userButtonLayout.getItemPosition(
                i), self.userButtonLayout.getItemPosition(j)

            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(i), *p2)
            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(j), *p1)
            self.target = None


class TestWidget(QtWidgets.QWidget):
    def __init__(self):
        QtWidgets.QWidget.__init__(self)

        self.test_widget = QtWidgets.QWidget()
        self.set_test()

        _layout = QtWidgets.QHBoxLayout()
        _layout.addWidget(CreateNodeBoard())
        _layout.addWidget(self.test_widget)

        self.setLayout(_layout)

    def set_test(self):
        """Adjacent test widget"""
        self.test_widget.setAutoFillBackground(True)
        self.test_widget.setPalette(QtGui.QColor(255, 0, 0))

        _test_layout = QtWidgets.QVBoxLayout()
        _test_layout.addWidget(QtWidgets.QLabel('TEST WIDGET'))

        self.test_widget.setLayout(_test_layout)


try:
    import nukescripts
except ImportError as error:
    APP = QtWidgets.QApplication(sys.argv)
    WINDOW = TestWidget()
    WINDOW.show()
    APP.exec_()
else:
    nukescripts.panels.registerWidgetAsPanel(
        'TestWidget', 'DragDrop',
        'DragDrop.MainWindow')

Solution

FOUND A FIX:

the dragEnterEvent caused the whole thing to go into recursion which causes the app to crash. (Linux terminal kept showing maximum recursion limit exceeded every time I moved the dragEvent outside the widgets area)

So to fix this I have created a condition inside the dragEnterEvent that if the mouse cursor moves outside the widgets it should ignore the event.

    ################################################################################
    # DRAG AND DROP
    ################################################################################

    def get_index(self, pos):
        for i in range(self.userButtonLayout.count()):
            buttonGlob = self.userButtonLayout.itemAt(i).widget().mapToGlobal(QtCore.QPoint(0,0)) 
            if QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(pos) and i != self.target:
                return i
    
    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.MiddleButton:           
            self.target = self.get_index(QtGui.QCursor.pos())
            if event.buttons() & QtCore.Qt.MiddleButton and self.target is not None:
                drag = QtGui.QDrag(self.userButtonLayout.itemAt(self.target).widget())
                pix = self.userButtonLayout.itemAt(self.target).widget().grab()
                mimedata = QtCore.QMimeData()
                mimedata.setImageData(pix)
                drag.setMimeData(mimedata)
                drag.setPixmap(pix)
                drag.setHotSpot(QtCore.QPoint(40,10))
                drag.exec_()
        else:
            self.target = None

    def dragLeaveEvent(self, event):
        if self.cursorInWidget():
            drag = QtGui.QDrag(self.userButtonLayout.itemAt(self.target).widget())
            drag.cancel()

    def cursorInWidget(self):
        cursorPos = QtGui.QCursor.pos()
        widgetWidth = self.nodeBoardWidget.geometry().width()
        widgetHeight = self.nodeBoardWidget.geometry().height()        
        widgetPos = self.nodeBoardWidget.mapToGlobal(QtCore.QPoint(0,0))
        if cursorPos.x() <= widgetPos.x() or cursorPos.y() <= widgetPos.y() or cursorPos.x() >= (widgetPos.x() + widgetWidth) or cursorPos.y() >= (widgetPos.y() + widgetHeight):
            return False
        else:
            return True

    def dragEnterEvent(self, event):
        if self.cursorInWidget():
            event.accept()
        else:
            event.ignore()

    def dropEvent(self, event):
        buttonGlob = self.userButtonLayout.itemAt(self.target).widget().mapToGlobal(self.pos())
        if not QtCore.QRect(buttonGlob.x(), buttonGlob.y(), 80, 23).contains(QtGui.QCursor.pos()):
            source = self.get_index(QtGui.QCursor.pos())
            if source is None:
                return
            i, j = max(self.target, source), min(self.target, source)
            p1, p2 = self.userButtonLayout.getItemPosition(i), self.userButtonLayout.getItemPosition(j)

            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(i), *p2)
            self.userButtonLayout.addItem(self.userButtonLayout.takeAt(j), *p1)
            self.target = None

Answered By - Filip Suska