Trying to capture the "mouse-dragging" status

[Bart Duijndam]

Hi, I started building a plugin for QGIS using PyQtGraph, as it is much quicker than MatPlotLib, and it is modeled around a scenegraph, which suits me fine.

I need to do a lot of custom drawing, so my code is built around the customGraphicsItem.py example.

My graphics class starts as follows:

class RollSurvey(pg.GraphicsObject):

    def __init__(self, name: str = 'Untitled')-> None:                          # assign default name value

        pg.GraphicsObject.__init__(self)

        etc...

To keep the paint effort manageable, I am using four different levels-of-detail (LOD) similar to the Qt 40000-chips example found here.

Here's my problem; in order to keep the plotting responsive when the user is panning the plot, I need to step back by (at least) one level-of-detail. But I have not been able to properly capture the mouse-down status, in order to reduce drawing effort whilst panning. The event sequence that I observe is :

QEvent::WindowActivate
QEvent::GrabMouse
QEvent::GraphicsSceneMousePress
QEvent::UngrabMouse
Painting - Mouse grabbed: False
Painting - Mouse grabbed: False
Painting - Mouse grabbed: False
Painting - Mouse grabbed: False
Painting - Mouse grabbed: False

I set the mouseGrabbed = True  condition when the "GrabMouse" event occurs and reset it at "UngrabMouse".

What I do not understand is that the mouse is already "ungrabbed" before painting starts...

Any suggestions what I am doing wrong / overlooking here ?

Thanks very much.