Ideal way to show markable text in QGraphicsScene

MS_GX · wrote on 18 Nov 2020, 10:28

My question is related to this question (https://forum.qt.io/topic/120114/how-to-select-only-part-of-a-text-of-qgraphictextitem) but more general now.

My setup:
Python 3.7.3
PySide2 5.15.1
OS: Debian

(I am quite a novice to Qt and GUI programming in general, just to provide some background)

I am showing text on a QGraphicsScene via using QGraphicsTextItem.

Everything works well so far. But I am really struggling with comming up with a solution in order to mark only parts of the text via mouse (click-drag-relase) like I would do in a webbrowser or in a word doc.

EDIT: The marked text then also needs to be copyable.

I was able to make the text selectable via setTextInteractionFlags(QtGui.Qt.TextSelectableByMouse) but this way I can only select the entire text of the QGraphicsTextItem.

So my questions:

Is QGraphicsTextItem the right type of widget for this? Is there anything better suited?
If it is the right type of widget: Can anyone hint me the right direction? Do I have to inherit QGraphicsTextItem and to catch the mouse events and do something on my own? Can I do this in PySide2? Or is there an already implemented way to do this?

So thankful for a hint!
Michael

SGaist · 19 Nov 2020, 09:01

Hi,

Can you provide a minimal runnable script that allows to test your issue ?

MS_GX · wrote on 19 Nov 2020, 08:16

Oh, while trying to set up a minimal example I discovered that QGraphicsTextIteam actually by default DOES what I want.

The problem is that I defined a new class deriving QGraphicsTextIteam and there I seem to have messed up!

I will make a minimal example with this new class and post it as soon as I am done.

MS_GX · 19 Nov 2020, 11:32

@SGaist

Now I have a working example. The problem was that I did not propagate the event (super().mousePressEvent(event)).

But now I have another problem. The application crahes with a segfault as soon as I do a right click. Probably this is my fault as well but I do not see what could cause it...

Here the minimal example:

from PySide2 import QtWidgets, QtCore, QtGui

class TextItem(QtWidgets.QGraphicsTextItem):
	
	def __init__(self):
		QtWidgets.QGraphicsTextItem.__init__(self)

	def mousePressEvent(self, event):

		if(event.button() == QtCore.Qt.MouseButton.LeftButton):		
			print("left button")

		if(event.button() == QtCore.Qt.MouseButton.RightButton):		
			print("right button")

		super().mousePressEvent(event)


class MainWindow(QtWidgets.QMainWindow):

	def __init__(self):

		super().__init__()

		self.setWindowTitle("Window title")

		self.scene = QtWidgets.QGraphicsScene()
		self.view = QtWidgets.QGraphicsView(self.scene)

		self.layout = QtWidgets.QHBoxLayout()
		self.layout.addWidget(self.view)
		self.setLayout(self.layout)

		self.setCentralWidget(self.view)


app = QtWidgets.QApplication([])

window = MainWindow()
window.resize(400, 100)
window.show()

text = TextItem()
text.setTextInteractionFlags(QtGui.Qt.TextSelectableByMouse)
text.setHtml("This is a test text text text text text text text text ...")
window.scene.addItem(text)

app.exec_()

MS_GX · wrote on 19 Nov 2020, 10:04

If I add this I do not get a segfault anymore:

def contextMenuEvent(self, event):
	event.ignore()

Is this a bug or a problem on my side?

JonB · 19 Nov 2020, 13:33

@MS_GX said in Ideal way to show markable text in QGraphicsScene:

The application crahes with a segfault as soon as I do a right click.

So do you run it from inside debugger and get the stack trace to see the cause? That's how we debug programs.

MS_GX · 19 Nov 2020, 13:41

@JonB

Thanks much!

I did some debugging and got the following (without capturing the contextMenuEvent for right button obviously):

(gdb) file python
Reading symbols from python...(no debugging symbols found)...done.
(gdb) run /home/user/SW/minimal_example/example.py
Starting program: /home/user/SW/venv/bin/python /home/user/SW/minimal_example/example.py
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7ffff4299700 (LWP 11120)]
[New Thread 0x7ffff1a98700 (LWP 11121)]
[New Thread 0x7fffef297700 (LWP 11122)]
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
[New Thread 0x7fffe1efa700 (LWP 11123)]
[New Thread 0x7fffdb76d700 (LWP 11124)]
[New Thread 0x7fffdaf4b700 (LWP 11125)]
[New Thread 0x7fffda71e700 (LWP 11126)]
[New Thread 0x7fffd9f0c700 (LWP 11127)]
[New Thread 0x7fffcb5ba700 (LWP 11128)]
[New Thread 0x7fffcadb9700 (LWP 11129)]
right button

Thread 1 "python" received signal SIGSEGV, Segmentation fault.
0x00007fffe91d3b58 in QWidget::window() const ()
   from /home/user/Software/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5

JonB · 19 Nov 2020, 13:52

@MS_GX
When the seg fault happens you need to look at the stack trace. That is a window if your are debugging inside Qt Creator, or the bt command if you are running gdb manually.

Having said. I'm not sure I appreciated you are running Python. I'm not certain gdb stack trace will be useful there, I don't know whether if you run inside a Python debugger you will have more joy.

Having said that: I just pasted your code and tried here on my Ubuntu 20.04/GNOME, and right-click was fine, it brought up the internal "Copy" menu.

MS_GX · 19 Nov 2020, 14:08

@JonB Thanks for the hints! Are you running Wayland or X11? Because I am running Wayland and I get this wayland warning there. Do you think that this might cause the problem?

Anyway, I will try to debug as you said. Many thanks!

JonB · 19 Nov 2020, 15:49

@MS_GX
Yup, I wouldn't know what "Wayland" was if it smacked me upside the head ;-) I am X11, vanilla Ubuntu 20.04 inside a vanilla Windows (7) PC with a vanilla gfx card/monitor. All drivers up-to-date.

MS_GX · J JonB 19 Nov 2020, 14:08

@JonB

Here the stacktrace for now. Not sure if helpful since I am not able to judge this to be honest.

(gdb) bt
#0  0x00007fffe91d3b58 in QWidget::window() const ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#1  0x00007fffe9389156 in QWidgetTextControlPrivate::contextMenuEvent(QPoint const&, QPointF const&, QWidget*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#2  0x00007fffe9389a9c in QWidgetTextControl::processEvent(QEvent*, QTransform const&, QWidget*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#3  0x00007fffe938065b in QWidgetTextControl::processEvent(QEvent*, QPointF const&, QWidget*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#4  0x00007fffe9472ecc in QGraphicsTextItem::dropEvent(QGraphicsSceneDragDropEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#5  0x00007fffe9e2ec2f in QGraphicsTextItemWrapper::contextMenuEvent(QGraphicsSceneContextMenuEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#6  0x00007fffe947f7e1 in QGraphicsItem::sceneEvent(QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#7  0x00007fffe947f985 in QGraphicsTextItem::sceneEvent(QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#8  0x00007fffe9e33c1d in QGraphicsTextItemWrapper::sceneEvent(QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#9  0x00007fffe94a02ed in QGraphicsScene::contextMenuEvent(QGraphicsSceneContextMenuEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#10 0x00007fffe9e165b7 in QGraphicsSceneWrapper::contextMenuEvent(QGraphicsSceneContextMenuEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#11 0x00007fffe94b0bd5 in QGraphicsScene::event(QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#12 0x00007fffe9e1802d in QGraphicsSceneWrapper::event(QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#13 0x00007fffe91ad3cc in QApplicationPrivate::notify_helper(QObject*, QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#14 0x00007fffe91b3eb0 in QApplication::notify(QObject*, QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#15 0x00007fffe9c835a5 in QApplicationWrapper::notify(QObject*, QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#16 0x00007fffe81bf0e8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) ()
   from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
--Type <RET> for more, q to quit, c to continue without paging--c
#17 0x00007fffe94ce8a2 in QGraphicsView::contextMenuEvent(QContextMenuEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#18 0x00007fffe9e40d67 in QGraphicsViewWrapper::contextMenuEvent(QContextMenuEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#19 0x00007fffe91ec398 in QWidget::event(QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#20 0x00007fffe929400e in QFrame::event(QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#21 0x00007fffe94ce2ab in QGraphicsView::viewportEvent(QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#22 0x00007fffe9e48d9d in QGraphicsViewWrapper::viewportEvent(QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#23 0x00007fffe81bee80 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#24 0x00007fffe91ad3a2 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#25 0x00007fffe91b5504 in QApplication::notify(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#26 0x00007fffe9c835a5 in QApplicationWrapper::notify(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#27 0x00007fffe81bf0e8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#28 0x00007fffe92050ca in QWidgetWindow::handleMouseEvent(QMouseEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#29 0x00007fffe9207c83 in QWidgetWindow::event(QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#30 0x00007fffe91ad3cc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#31 0x00007fffe91b3eb0 in QApplication::notify(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Widgets.so.5
#32 0x00007fffe9c835a5 in QApplicationWrapper::notify(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#33 0x00007fffe81bf0e8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#34 0x00007fffe88886d6 in QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::MouseEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Gui.so.5
#35 0x00007fffe8889ae5 in QGuiApplicationPrivate::processWindowSystemEvent(QWindowSystemInterfacePrivate::WindowSystemEvent*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Gui.so.5
#36 0x00007fffe88658cb in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Gui.so.5
#37 0x00007fffe2e4157a in xcbSourceDispatch(_GSource*, int (*)(void*), void*) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/plugins/platforms/../../lib/libQt5XcbQpa.so.5
#38 0x00007fffe5134f2e in g_main_context_dispatch () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#39 0x00007fffe51351c8 in ?? () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#40 0x00007fffe513525c in g_main_context_iteration () from /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#41 0x00007fffe821aaac in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#42 0x00007fffe81bdafa in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#43 0x00007fffe81c6ab3 in QCoreApplication::exec() () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/Qt/lib/libQt5Core.so.5
#44 0x00007fffe9c81038 in Sbk_QApplicationFunc_exec_ () from /home/user/SW/venv/lib/python3.7/site-packages/PySide2/QtWidgets.abi3.so
#45 0x00000000005d7061 in _PyMethodDef_RawFastCallKeywords ()
#46 0x000000000054aac0 in ?? ()
#47 0x0000000000551bf9 in _PyEval_EvalFrameDefault ()
#48 0x000000000054b452 in _PyEval_EvalCodeWithName ()
#49 0x000000000054d7f3 in PyEval_EvalCode ()
#50 0x0000000000630152 in ?? ()
#51 0x0000000000630207 in PyRun_FileExFlags ()
#52 0x0000000000630e6f in PyRun_SimpleFileExFlags ()
#53 0x0000000000653eae in ?? ()
#54 0x000000000065420e in _Py_UnixMain ()
#55 0x00007ffff79c109b in __libc_start_main (main=0x4bc8d0 <main>, argc=2, argv=0x7fffffffd748, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffd738) at ../csu/libc-start.c:308
#56 0x00000000005df66a in _start ()