pyqtgraph中的可控贝塞尔曲线控制器

Question

I want to construct a plot item with a controlable bezier curve (using 4 points)

c3 = -P1 + 3 * (P2 - P3) + P4
c2 = 3 * (P1 - (2 * P2) + P3)
c1 = 3 * (P2 - P1)
c0 = P1

curve = ((c3 * time_points + c2) * time_points + c1) * time_points + c0

I would like something that look like this:

My question is, what would be the most straightforward way of implementing this in pyqtgraph. I see two ways:

• from scratch, using PlotDataItem. I started this but I don't know how to make the dragging feature working without subclassing everything
• subclassing the ROI class, but I have some trouble understanding how this class works exactly, it seems that everything is in relative coordinates, I need to find the right track

Thanks for any insight on this !

Answer 1

Ok, after some research, I found an example implementation of an bezier ROI using pyqtgraph. Here is a link to the github repository

Basically it is about subclassing ROI class, using a freehandle type of handle (which is not relative). and painting the bezier curve (by "hand").

There is also the qt toCubic function that draw bezier.

Using ROI allows to get all the features of ROI, that I would have to implement from scratch if I had chosen using PlotDataItem. It is still not so obvious, and a good understanding of pyqt seems necessary to get everything in place for the ROI to work as expected.

I hope this will help others