Plotter in Qt - Mouse Click Event not registering at the correct position

I have tried several different things about the mouse clicks not registering correctly in my Qt mainwindow. When using only my QHD monitor, the program worked just fine (video). However, when using my laptop (zoomed in at 1792 x 1120) as the only display, the mouse clicks seemed to have a varying up-right offset and register more accurately near the bottom left corner of the widget (video). I am suspicious that the screen resolution of the display might cause a problem for vedo.

The mouse event is a vedo plotter event. Changing the “screensize”, “size”, “pos” attribute of the plotter did not fix the issue.

I looked up some examples provided by vedo, specifically mousehover.py and qt_window1.py. The mousehover example worked fine on my laptop. However, adding a clicking event in qt_window1.py also created the same issue. Therefore, the problem most likely was caused by the qt widget.

    def __init__(self,size):
        super(MainWindow, self).__init__()

        # load the components defined in th xml file
        loadUi("viewer_gui.ui", self)
        self.screenSize = size

        # Connections for all elements in Mainwindow
        self.pushButton_inputfile.clicked.connect(self.getFilePath)
        self.pushButton_clearSelection.clicked.connect(self.clearScreen)
        self.action_selectVertex.toggled.connect(self.actionSelection_state_changed)
        self.action_selectActor.toggled.connect(self.actionSelection_state_changed)

        # Set up VTK widget
        self.vtkWidget = QVTKRenderWindowInteractor()
        self.splitter_viewer.addWidget(self.vtkWidget)

        # ipy console
        self.ipyConsole = QIPythonWidget(customBanner="Welcome to the embedded ipython console\n")
        self.splitter_viewer.addWidget(self.ipyConsole)
        self.ipyConsole.pushVariables({"foo":43, "print_process_id":print_process_id, "ipy":self.ipyConsole, "self":self})
        self.ipyConsole.printText("The variable 'foo' and the method 'print_process_id()' are available.\
            Use the 'whos' command for information.\n\nTo push variables run this before starting the UI:\
                \n ipyConsole.pushVariables({\"foo\":43,\"print_process_id\":print_process_id})")

        # Create renderer and add the vedo objects and callbacks
        self.plt = Plotter(qtWidget=self.vtkWidget,bg='DarkSlateBlue',bg2='MidnightBlue',screensize=(1792,1120))
        self.id1 = self.plt.addCallback("mouse click", self.onMouseClick)
        self.id2 = self.plt.addCallback("key press",   self.onKeypress)
        self.plt.show()                  # <--- show the vedo rendering

    def onMouseClick(self, event):
        if(self.action_selectActor.isChecked()):
            self.selectActor(event)
        elif(self.action_selectVertex.isChecked()):
            self.selectVertex(event)

    def selectActor(self,event):
        if(not event.actor):
            return
        printc("You have clicked your mouse button. Event info:\n", event, c='y')
        printc("Left button pressed on", [event.picked3d])
        # adding a silhouette might cause some lags
        # self.plt += event.actor.silhouette().lineWidth(2).c('red')
        #an alternative solution
        self.actorSelection = event.actor.clone()
        self.actorSelection.c('red')
        self.plt += self.actorSelection

    def selectVertex(self,event):
        if(not event.isPoints):
            return
        # print(arr[event.actor.closestPoint(event.picked3d, returnPointId=True)])
        printc("You have clicked your mouse button. Event info:\n", event, c='y')
        printc("Left button pressed on 3d: ", [event.picked3d])
        printc("Left button pressed on 2d: ", [event.picked2d])
        p = pointcloud.Point(pos=(event.picked3d[0],event.picked3d[1],event.picked3d[2]),r=12,c='red',alpha=0.5)
        self.vertexSelections.append(p)        
        self.plt += p

Running the following lines:

app = QApplication(sys.argv)
screen = app.primaryScreen()
print('Screen: %s' % screen.name())
size = screen.size()
print('Size: %d x %d' % (size.width(), size.height()))

outputted

Screen: Color LCD
Size: 1792 x 1120

[p-j-smith]

Hi, I’m very new to vedo (thanks for making such a great library!), but I’ve come across this issue with vtk before. Based on the comments in a previous issue related to this problem, it sounds like there is no plan to fix it as vtkmodules/qt/QVTKRenderWindowInteractor.py is not maintained by the core VTK devs. But I’m sure they’d be open to someone submitting a fix.

There used to be the opposite problem whereby coordinates would be scaled by a factor of 0.5, so a fix was made for this in QVTKRenderWindowInteractor. However, this fix is no longer necessary (possibly due to changes made in qt), and so the original fix is now actually a bug. The fix introduced a method _getPixelRatio, which determines the factor by which coordinates needed to be scaled to fix the previous bug (and on Mac retina displays this was a factor of two). As no scaling needs to be applied, I’ve been using a hacky fix to make this method always return a value of 1:

interactor = QVTKRenderWindowInteractor()
interactor._getPixelRatio = lambda _: 1

[danieljiang520]

After downgrading VTK to version 8.1.2 and Python to 3.7, the clicking issue disappeared when running the program on my laptop. Thank you for the help! I will keep an eye on new releases from vtk.