Immediate update when GraphicsObject changes

[Magne Lauritzen]

Good day.

I am attempting to rapidly animate an ellipse in the form of a GraphicsObject in a PlotWidget. When the parameters of the ellipse changes, I call the requisite :

            self.update()

            self.informViewBoundsChanged()

However, this appears to only schedule an update of the scene for later. This is not sufficient for me, as I will be rapidly updating the parameters of the GraphicsObject and require update speeds on the same order as PlotDataItem, i.e. near-instantaneous.

Could this perhaps be solved by subclassing an implementation of Viewbox that catches an emitted signal from the GraphicsObject and forces an update? I believe this is how instantaneous updates of PlotDataItem is achieved, through the sigPlotChanged signal.

Anyways, the following is the class definition for the custom ellipse GraphicsObject. 

class EllipseItem(pg.GraphicsObject):

    def __init__(self, center:Union[float,List[float]], radius:Union[float,List[float]]):

        pg.GraphicsObject.__init__(self)

        self.center = None

        self.radius = None

        self.setCenter(center)

        self.setRadius(radius)

    

    def setCenter(self,center:Union[float,List[float]]):

        self.center = center

        self.generatePicture()

        

    def setRadius(self,radius:Union[float,List[float]]):

        self.radius = radius

        self.generatePicture()

        

    def generatePicture(self):

        if self.center is not None and self.radius is not None:

            self.picture = QtGui.QPicture()

            p = QtGui.QPainter(self.picture)

            p.setPen(pg.mkPen('w'))

            try:

                r1 = self.radius[0]

                r2 = self.radius[1]

            except (TypeError, IndexError):

                r1 = r2 = self.radius

            try:

                c1 = self.center[0] - r1

                c2 = self.center[1] - r2

            except (TypeError, IndexError):

                c1 = self.center - r1

                c2 = self.center - r2            

            p.drawEllipse(QtCore.QRectF(c1,c2,r1*2,r2*2))

            p.end()

            self.update()

            self.informViewBoundsChanged()

      

    def paint(self, p, *args):

        p.drawPicture(0, 0, self.picture)

    def boundingRect(self):

        return QtCore.QRectF(self.picture.boundingRect())

The following is a minimal working example showing that update is not immediate. Note the delay between updating the radius of the Ellipse and the change becoming apparent in the PlotWindow.

from <filename> import EllipseItem

pw = pg.PlotWidget()

item = EllipseItem([0,1],[1,0.5])

plotui.addItem(item)
item.setRadius([0.5,1])

Regards,

Magne Lauritzen

[Magne Lauritzen]

Apologies, the minimum working example had a mistake in it. Here is the corrected code:

from <filename> import EllipseItem

pw = pg.PlotWidget()

item = EllipseItem([0,1],[1,0.5])

pw.addItem(item)
item.setRadius([0.5,1])