Excalidraw: line editing: make point-adding more obvious

[dawneraq]

@vjeux mentioned on Twitter that there was some discussion about presenting an affordance, indicating that a new point can be added, when a user hovers over a line's point in edit mode. He also said there was no issue open for this yet.

We should make it more obvious, one of the proposals was to add a shadow point on mouse over near the middle.

(Personally, I deleted and redrew a line 3 times before noticing the hint at the top of the screen saying I could add points in edit mode. 😅)

I'm guessing the shadow point would behave something like this:

IMO, when a point is selected, the cursor doesn't necessarily have to be hovering over that point for a shadow point to be previewed.

For case F (extending a line), it might make sense to display the shadow point at a distance that's the same as halfway between P3 and P2, just in the opposite direction. Thoughts?

Related issues

• This likely falls under "add hover state for points" in #1985.

• Directly related to #1895

[vjeux]

Love the use of excalidraw for explaining the behavior you have in mind!