Editing line points or vertices of a polygon is a recurring question I see in the Konva Discord. It gets tricky when the line or its parents are affected by transforms. Here's how to make a bulletproof solution that handles that.
We are often required to position shapes relative to each other - maybe circles mark points on a line - but then you move one of the shapes and update the others position but it doesn't make sense. The answer is relativity!
So you have a shape with some transforms applied - you need to apply the same transforms to another shape. How do you do that ?
The Konva HTML5 canvas lib has a very useful feature that can spit out the transformations applied to a shape, and which we can borrow to rotate points without math. Lets take a look...