plot: Slow down with big polyline Shapes

[vallsv]

Hi,

I am displaying a lot of polylines Shape to mark some locations in an image.

It sounds like it slow down a lot the rendering.

Playing with the flag setOverlay does'nt change much.

Previously i was using Curve for the rendering, but this does not feature double colors.

Here is a piece of code

                    if True:
                        ringItem = silxItems.Shape("polylines")
                        ringItem.setPoints(numpy.array((x, y)).T)
                        ringItem.setName(key)
                        ringItem.setLineStyle("--")
                        ringItem.setColor("#FF0000A0")
                        ringItem.setLineBgColor("#FFFFFFA0")
                    else:
                        # The implementation with shape have some lacks
                        # Maybe we will have to fall down with curves
                        ringItem = FlintRingCurve()
                        ringItem.setRing(ring)
                        ringItem.setData(x, y)
                        ringItem.setName(key)
                        ringItem.setColor("#FFFFFFA0")
                        ringItem.setLineStyle("--")

The use case is really to put some location on top of the image. It is not supposed to be updated often (up until now), so it is really a problem of rendering.