Bezier line doesn't update to reflect the latest node handle position and is not tangent to them. Also, updating is very slow.
Summary:
When quickly moving node handles around, the underlying line sometimes doesn't update to reflect their position. So what you can end up with is your node handles drawn in one direction, but the underlying line not being parallel (tangent) to this direction as it should. Moving another node will quickly snap the line correctly.
Another thing is that updating the line is embarrassingly slow. I just tried doing the same on my 30 year old Macintosh IIsi running at 20MHz with Adobe Illustrator 5.5, and it's faster at redrawing the curve than Inkscape on this 2020 MacBook Pro with 32MB RAM.
Steps to reproduce:
- Draw a freehand line with some wiggles, make it black, 1px
- Zoom in on the line so that the line width spans approx. 5px wide on your screen, see screenshot (not sure this is necessary)
- Select the edit nodes tool (N)
- Select one node on the line, then find its handles, select one of these handles and rapidly move it up and down or sideways back and forth.
- Release the mouse button (while moving)
- Observe: 1. The refresh rate is slow. 2. Worse: sometimes, like maybe 50% of the time, the underlying line doesn't update to reflect the latest handle position.
- Moving another node ever so slightly will "snap" the line into the correct orientation.
So what you can end up with is your node handles drawn in one direction, but the underlying line not being parallel (tangent) to this direction as it should, and is stays this way even after waiting a minute. Moving another node will quickly snap the line correctly.
What happened?
The line is not tangent to the direction of the handles.
What should have happened?
It should be tangent. I.e., the line should be parallel to the handles at the point where the handles cross the line.
Sample attachments:
This should never be possible, at least not while it's done updating:
The line snaps back to be tangent to the node handles when moving another node:
Version info
Inkscape 1.2.1 (9c6d41e4, 2022-07-14)
GLib version: 2.70.5
GTK version: 3.24.33
glibmm version: 2.60.0
gtkmm version: 3.24.5
libxml2 version: 2.9.12
libxslt version: 1.1.34
Cairo version: 1.17.6
Pango version: 1.50.6
HarfBuzz version: 2.9.1
OS version: macOS